JP4459930B2 - Perpendicular magnetic recording type information recording medium - Google Patents

Description

  The present invention relates to an information recording medium that records and reproduces information by magnetic action, such as a magnetic disk, and particularly relates to a technology that focuses on increasing the density of the information recording medium.

  In recent years, the amount of information handled has become enormous with the arrival of an advanced information society. Therefore, there is a demand for an increase in capacity and density of the recording apparatus. In particular, a magnetic recording apparatus with a low bit unit price and capable of non-volatile and large-capacity recording is one of the most widely used storage apparatuses, and development of a magnetic recording medium capable of high-density recording is strongly demanded.

  However, in the longitudinal magnetic recording type magnetic recording medium, the recording magnetization becomes unstable due to thermal energy at room temperature. Therefore, if the recording density is further increased, it becomes difficult to hold the recording bits for a long period of time. Therefore, it is difficult to further improve the recording density in the conventional longitudinal magnetic recording type magnetic recording medium.

  On the other hand, a perpendicular magnetic recording type magnetic recording medium has a characteristic that the recording magnetization is stabilized as the density is increased. Therefore, the recording system of the magnetic recording medium is shifting to the perpendicular magnetic recording system.

  A magnetic recording medium using a perpendicular magnetic recording system generally includes a recording layer that records and holds magnetization information, and a soft magnetic backing layer that plays a role of concentrating the recording magnetic field generated by the magnetic head in the recording layer. Is done.

  Here, the soft magnetic backing layer made of a soft magnetic material such as a nickel-iron (NiFe) alloy is divided into magnetic domains each having a different magnetization direction in the layer. And a big leakage magnetic flux generate | occur | produces from the domain wall which is a boundary of a magnetic domain and a magnetic domain. The large leakage magnetic flux from the soft magnetic under layer causes a large noise called spike noise during signal reproduction.

  As a method for suppressing spike noise from a soft magnetic backing layer, Patent Document 1 provides an antiferromagnetic layer made of a manganese-based antiferromagnetic material and a soft magnetic backing layer on a substrate so as to be in contact with each other. A technique is disclosed in which the domain wall is controlled by coupling to suppress the formation of the domain wall in the soft magnetic underlayer. Thereby, the leakage magnetic flux from the soft magnetic backing layer is suppressed, and spike noise is reduced.

  The magnetic recording medium described in Patent Document 2 is a perpendicular recording type including at least a perpendicular magnetic recording layer and a backing layer that lines the perpendicular magnetic recording layer and has magnetization in a direction perpendicular to the stacking direction. In the magnetic recording medium, the backing layer is formed of a ferrimagnetic material having a compensation temperature in the vicinity of a temperature at which magnetic information recorded in the perpendicular magnetic recording layer is reproduced.

  By forming the backing layer with the above configuration, when magnetic information is recorded on the perpendicular magnetic recording layer, the backing layer has magnetization and reproduces the magnetic information recorded on the perpendicular magnetic recording layer. In some cases, the backing layer may have no magnetization.

Therefore, according to the magnetic recording medium described in Patent Document 2, it is possible to suppress noise from the backing layer during signal reproduction.
Japanese Patent Laid-Open No. 10-214719 (Publication date: August 11, 1998) International Publication WO 02/095739 (International Publication Date November 28, 2002) Hiroaki Wakamatsu et al., Journal of Japan Society of Applied Magnetics, Vol. 17, no. 5, 1993, p792-p796

  However, even if the magnetic recording medium described in Patent Document 1 suppresses the formation of the domain wall in the soft magnetic underlayer, the spike noise has not been sufficiently reduced.

  On the other hand, according to the magnetic recording medium described in Patent Document 2, the problem of spike noise is solved.

  However, it is difficult to accurately and uniformly record minute recording marks on the magnetic recording medium described in Patent Document 2. This is because it is difficult for the recording magnetic field induced to the backing layer during signal recording to form a smooth magnetic closed circuit between the magnetic head of the information recording apparatus or information recording / reproducing apparatus and the backing layer. Because. The backing layer of the magnetic recording medium described in Patent Document 2 is formed using a rare earth metal-transition metal alloy which is a ferrimagnetic material having a compensation temperature. Therefore, the magnetic anisotropy energy in the direction perpendicular to the stacking direction (hereinafter referred to as in-plane magnetic anisotropy energy) is an order of magnitude smaller than that of a soft magnetic backing layer formed of a soft magnetic material. . This was the reason why a smooth magnetic closed circuit could not be made.

  More specifically, a backing layer formed of a ferrimagnetic material has a small in-plane magnetic anisotropy energy. Therefore, the magnetization direction in the layer has a degree of freedom with respect to the stacking direction. As a result, it is dragged by the recording magnetic field, and the magnetization direction fluctuates from the direction perpendicular to the stacking direction. As a result, the recording magnetic field induced to the backing layer is disturbed, and the magnetic closed circuit formed between the magnetic head and the backing layer is not smooth. Therefore, it becomes difficult to record minute recording marks accurately and uniformly.

  In general, it has been reported that the thicker the backing layer, the more efficiently the magnetic field from the magnetic head can be concentrated and applied to the recording layer (Hiroshi Wakamatsu et al., Journal of Applied Magnetics Society of Japan, Vol. 17, No. 17). ., 1993, p792-p796). On the other hand, as the film thickness of the backing layer increases, the in-plane magnetic anisotropy energy of the backing layer decreases due to the shape of the film. That is, in order to efficiently concentrate the magnetic field from the magnetic head on the recording layer, it is preferable to increase the thickness of the backing layer. In this case, however, the in-plane magnetic anisotropy energy of the backing layer is further reduced. End up. On the other hand, if the thickness of the backing layer is reduced, the magnetic field from the magnetic head cannot be efficiently concentrated on the recording layer, which is not preferable.

  Therefore, when the backing layer is formed of a ferrimagnetic material or the like in order to reduce spike noise, the fineness, accuracy, and uniformity of recording marks that can be recorded on the recording layer are limited to some extent. .

  The present invention has been made in view of the above-mentioned problems, and its object is to have better signal reproduction characteristics than a conventional magnetic recording medium composed of a recording layer and a soft magnetic backing layer, and it is very small even during recording. It is an object of the present invention to provide an information recording medium capable of accurately recording uniform recording marks.

  In order to solve the above problems, an information recording medium according to the present invention includes a recording layer on which an information signal is magnetically recorded, and a backing layer for concentrating the magnetic field used for recording the information signal on the recording layer. The backing layer is provided below the recording layer, and is formed by alternately laminating a plurality of secondary backing films and at least one nonmagnetic film made of a nonmagnetic material, and the secondary backing film is The information signal has a magnetization perpendicular to the stacking direction at the recording temperature of the information signal, and the magnetization is smaller at the reproducing temperature of the information signal than at the recording temperature of the information signal. And In particular, it is preferable that the sub-lining film has zero magnetization at substantially the same temperature as the information signal reproduction temperature.

  The reproduction temperature of the information signal (hereinafter referred to as signal reproduction temperature) is the temperature of the information recording medium at the time of reproduction of the information signal (hereinafter referred to as signal reproduction). The recording temperature of the information signal (hereinafter referred to as signal recording temperature) is the temperature of the information recording medium when the information signal is recorded (hereinafter referred to as signal recording).

  According to the above configuration, at the time of signal reproduction, the secondary backing film constituting the backing layer has a small magnetization, preferably zero. Therefore, generation of leakage magnetic flux during signal reproduction can be suppressed. This suppresses the occurrence of spike noise. Therefore, when reproducing the information signal of the information recording medium, noise from the backing layer can be reduced or eliminated, the quality of the reproduced information signal can be improved, and good signal characteristics can be obtained.

  Note that the magnetization becomes zero at substantially the same temperature as the signal reproduction temperature, to the extent that spike noise from the backing layer is sufficiently suppressed when reproducing the information signal of the information recording medium. It means that the amount of magnetization of the backing layer approaches zero.

  Further, according to the above configuration, at the time of signal recording, the secondary backing film constituting the backing layer has magnetization in a direction perpendicular to the stacking direction. Thereby, when recording an information signal on the recording layer, a magnetic closed circuit can be formed between the magnetic head and the backing layer via the recording layer. That is, a magnetic field induced from the magnetic head to the backing layer is applied to the recording layer. Therefore, since the magnetic field from the magnetic head can be efficiently concentrated and applied, the strength and gradient of the magnetic field applied to the recording layer can be increased.

  However, the secondary backing film as described above may have a small in-plane magnetic anisotropy energy like the backing layer described in Patent Document 2. In addition, as described above, the thicker the backing layer, the more efficiently the magnetic field from the magnetic head can be concentrated and applied to the recording layer. preferable. If the thickness of the sub-backing film is large, the in-plane magnetic anisotropy energy is further reduced due to its shape.

  Here, according to the above configuration, the backing layer is formed by alternately laminating a plurality of secondary backing films and at least one nonmagnetic film made of a nonmagnetic material. In the following, a comparison is made between the backing layer and a conventional case where the backing layer is formed of a single film. The film thickness of the single film is the same as the total thickness of the sub-backing films.

  First, in the backing layer and the backing layer formed by the single film, similarly, the magnetic field from the magnetic head can be efficiently concentrated and applied to the recording layer. That is, as described above, generally, the thicker the backing layer, the more efficiently the magnetic field from the magnetic head can be applied to the recording layer. The same effect can be obtained also by increasing the value.

  At the same time, the thickness of each of the sub-lining films is naturally smaller than that of the single film. In general, the in-plane magnetic anisotropy energy of a thin film increases as the film thickness decreases. Therefore, the in-plane magnetic anisotropy energy of the sub-backing film is higher than the in-plane magnetic anisotropy energy of the single film. Each sub-backing film is magnetically separated by the non-magnetic film, so that the energy is not reduced by the mutual magnetic influence.

  Since the in-plane magnetic anisotropy energy of the sub-backing film is high, the magnetization of the sub-backing film is fixed in a direction perpendicular to the stacking direction without having a degree of freedom in the stacking direction. Therefore, the write magnetic field generated from the magnetic head is guided by the magnetization of the sub-backing film and flows in a certain direction along the magnetization. As a result, a smooth magnetic closed circuit is formed between the magnetic head and the backing layer. Thereby, minute recording marks can be accurately and uniformly recorded on the recording layer.

  As described above, according to the above configuration, the signal reproduction characteristic is superior to that of a magnetic recording medium composed of a conventional recording layer and a soft magnetic backing layer, and minute marks are recorded accurately and uniformly even during recording. It is possible to provide an information recording medium that can be used.

  In the information recording medium according to the present invention, it is preferable that the sub-backing film is made of a ferrimagnetic material having a compensation temperature that is substantially the same as the reproduction temperature of the information signal.

  The ferrimagnetic material has a compensation temperature at which the amount of magnetization becomes zero. According to the above configuration, at the reproduction temperature of the information signal (hereinafter referred to as signal reproduction temperature), the magnetization of the backing layer can be made small, for example, zero or substantially zero. That is, at the time of reproducing the information signal recorded on the recording layer of the information recording medium, the sub-backing film has a small magnetization (becomes zero) and can suppress (do not emit) leakage magnetic flux. Therefore, there is an effect that spike noise can be more effectively suppressed.

  In the information recording medium according to the present invention, the ferrimagnetic material is an alloy including at least one element selected from rare earth metal elements and at least one element selected from transition metal elements. Is preferred.

  Rare earth metal-transition metal alloys are ferrimagnetic materials, and their magnetic characteristics change sharply with temperature. Furthermore, the compensation temperature and the Curie temperature can be set to desired temperatures by changing the composition ratio between the rare earth metal and the transition metal. Therefore, according to the said structure, there exists an effect that the sub-backing film | membrane along the objective of this invention can be produced easily.

  In the information recording medium according to the present invention, the rare earth metal element is preferably at least one of gadolinium and holmium. The transition metal element is preferably at least one selected from the group consisting of iron, cobalt, and nickel.

  According to the above configuration, the sub-backing film is formed of an alloy including at least one of gadolinium and holmium and at least one selected from the group consisting of iron, cobalt, and nickel. Thereby, the sub-backing film has a large magnetization in a direction perpendicular to the stacking direction of each layer of the information recording medium in a high temperature region of 150 ° C. or higher. Therefore, the alloy can be suitably used as a material for forming the sub-lining film.

  In the information recording medium according to the present invention, it is preferable that the average thickness of the auxiliary backing film is 5 nm or more and 25 nm or less.

  Here, the average film thickness refers to the average value of the thicknesses of the one auxiliary backing film in the one information recording medium. For example, it can be obtained by measuring the film thickness at a plurality of arbitrary positions of the one sub-backing film and averaging it. Hereinafter, the same applies to the average film thicknesses of the other layers.

  According to the above configuration, since the average thickness of the secondary backing film is 5 nm or more, the magnetic characteristics of each secondary backing film can be stably maintained. At the same time, since the sub-backing film has an average film thickness of 25 nm or less, the in-plane magnetic anisotropy energy of the sub-backing film can be sufficiently increased.

  In the information recording medium according to the present invention, it is further preferable that the nonmagnetic film has an average film thickness of 1 nm or more and 3 nm or less.

  According to the above configuration, since the average thickness of the nonmagnetic film is 1 nm or more, each sub-backing film can be magnetically separated. Therefore, the magnetic anisotropy of each sub-backing film can be stably maintained in the direction perpendicular to the stacking direction. At the same time, since the average film thickness of the nonmagnetic film is 3 nm or less, the distance between each of the sub-backing films located farther from the magnetic head than the nonmagnetic film and the magnetic head can be shortened. Therefore, the backing layer has an effect that the magnetic field from the magnetic head can be efficiently induced.

  The information recording medium according to the present invention preferably further includes a nonmagnetic intermediate layer between the backing layer and the recording layer.

  As described above, when the information signal is recorded on the recording layer, the sub backing layer constituting the backing layer has magnetization in a direction perpendicular to the stacking direction. On the other hand, for the recording layer, it is necessary to record magnetization in the stacking direction.

  Here, according to the above configuration, the nonmagnetic intermediate layer is interposed between the backing layer and the recording layer. For this reason, the magnetic exchange interaction between the backing layer and the recording layer can be hardly exerted. Therefore, it is possible to prevent the magnetization direction of the recording layer from being dragged to the magnetization direction of the backing layer during signal recording. As a result, there is an effect that magnetization can be stably recorded in the stacking direction with respect to the recording layer.

  In the information recording medium according to the present invention, it is further preferable that the nonmagnetic intermediate layer has an average film thickness of 5 nm or less.

  According to the above configuration, since the average film thickness of the nonmagnetic intermediate layer is as thin as 5 nm or less, the distance in the film thickness direction between the magnetic head and the backing layer is short. Therefore, at the time of signal recording, the backing layer can easily induce a magnetic field from the magnetic head. Therefore, it is possible to increase the strength and gradient of the recording magnetic field applied to the recording layer during signal recording and improve the recording resolution of the information recording medium.

  In the information recording medium according to the present invention, the nonmagnetic intermediate layer further includes a dielectric layer formed of a dielectric and an uneven layer formed on the dielectric layer, wherein the uneven layer is It is preferable that the surface has an uneven shape at the interface with the recording layer.

  According to the above configuration, the nonmagnetic intermediate layer includes the dielectric layer and the uneven layer. Furthermore, the uneven layer has an uneven shape at the interface with the recording layer. Since the recording layer is formed on the uneven layer, the recording layer has an uneven shape corresponding to the uneven shape. This uneven shape limits the movement of the domain wall in the recording layer. That is, the movement of the domain wall formed in the recording layer is limited to the concave and convex portions formed by the concave and convex shapes. As a result, when the information signal is recorded on the recording layer, the movement of the domain wall is limited to a short distance as compared with the case where the uneven shape does not exist at the interface between the recording layer and the uneven layer. Thus, it is possible to stably write a magnetic field on the recording layer and to obtain good signal reproduction characteristics when reproducing the information recording medium.

  In the information recording medium according to the present invention, the dielectric layer is preferably formed of at least one of a nitride and an oxide.

  According to the above configuration, the dielectric layer is made of nitride or oxide. Here, the nonmagnetic metal particles constituting the metal film (nonmagnetic metal film) are unlikely to diffuse on the nitride or oxide. Therefore, when a nonmagnetic metal film is formed on the dielectric layer, it is not uniformly formed and an uneven shape is easily formed. Therefore, by utilizing this property, there is an effect that the uneven layer can be easily formed.

  In the information recording medium according to the present invention, it is preferable that the uneven layer is made of aluminum.

  According to the said structure, the uneven | corrugated layer which has fine uneven | corrugated shape can be formed. In addition, it is easy to keep the uneven shape at the interface between the uneven layer and the recording layer. Therefore, according to the above configuration, it is possible to suitably and easily form a concavo-convex layer having a concavo-convex shape, and it is possible to more effectively prevent the domain wall from moving in the recording layer.

  In the information recording medium according to the present invention, it is preferable that the average thickness of the dielectric layer is 2 nm or less. The uneven layer preferably has an average film thickness of 3 nm or less.

  According to said structure, the average film thickness of a nonmagnetic intermediate | middle layer can be formed in 5 nm or less. This shortens the distance between the magnetic head and the backing layer. Therefore, when recording an information signal, the backing layer can easily induce a magnetic field from the magnetic head. Furthermore, it is possible to prevent the entire information recording medium from being thickened.

  In the information recording medium according to the present invention, it is preferable that the average surface roughness (Ra) of the uneven layer at the interface with the recording layer is 0.6 nm or more and 1.5 nm or less.

  According to the said structure, the average surface roughness of an uneven | corrugated layer is 0.6 nm or more and 1.5 nm or less. Therefore, the concavo-convex layer can effectively suppress the movement of the domain wall in the recording layer. Thus, it is possible to stably write a magnetic field on the recording layer and to obtain good signal reproduction characteristics when reproducing the information recording medium.

  In the information recording medium according to the present invention, it is further preferable that the average diameter of the convex portions of the concavo-convex layer at the interface with the recording layer is 50 nm or less.

  According to the above configuration, a minute uneven shape can be formed at the interface between the uneven layer and the recording layer. Thereby, the movement of the domain wall in the recording layer can be effectively suppressed. Thus, it is possible to stably write a magnetic field on the recording layer and to obtain good signal reproduction characteristics when reproducing the information recording medium. The average diameter is obtained by approximating the convex portion with a cone and obtaining an average value of the diameters of the bottom surfaces. However, this does not limit the shape of the convex portion to a conical shape.

  Since the information recording medium according to the present invention forms the backing layer by alternately stacking the nonmagnetic film and the sub-backing film as described above, the in-plane magnetic anisotropy energy of the backing layer can be increased. . Further, since the sub-backing film has magnetization in a direction perpendicular to the laminating direction at the signal recording temperature and has almost no magnetization at the signal reproduction temperature, no leakage magnetic flux is generated during reproduction. Therefore, minute recording marks can be recorded accurately and uniformly while avoiding the occurrence of spike noise.

  Embodiments of the information recording medium of the present invention will be described below with reference to the accompanying drawings.

  In the following embodiment, the information recording medium of the present invention is applied to a magnetic disk.

[First Embodiment]
The first embodiment of the present invention will be described below.

(Explanation of membrane structure)
FIG. 1 is a cross-sectional view showing a film configuration of an information recording medium 1 according to this embodiment. As shown in FIG. 1, the information recording medium 1 includes a substrate 3, a backing layer 6 in which sub-backing films 5 and nonmagnetic films 4 are alternately stacked, a recording layer 10, a protective layer 11, and a lubricating layer 12. These are stacked in this order.

(Description of substrate 3)
The substrate 3 is a support for forming and laminating the above layers. Therefore, the substrate 3 is only required to be made of a nonmagnetic material, have a smooth surface on which the layers are laminated, and be made of a material that can hold the layers without deformation during film formation. The material of the substrate 3 is not particularly limited, and specifically, glass, aluminum, plastic, silicon, or the like can be used.

  Further, the shape of the substrate 3 is not particularly limited. For example, a flat plate shape, a disk shape, or a cylinder shape can be used. In the case where a cylindrical shape is used as the shape of the substrate 3, the above layers are laminated on the cylinder outer peripheral side surface. In addition, it is preferable to clean the surface of the substrate 3 by reverse sputtering or the like before laminating the above layers.

  Hereinafter, a case where flat plate-like glass is used as the substrate 3 will be described.

(Description of backing layer 6)
The backing layer 6 is provided for concentrating the write magnetic field generated by the magnetic head on the recording layer 10 when recording information on the information recording medium 1 using the magnetic head. That is, the backing layer 6 has magnetization in a direction perpendicular to the stacking direction (hereinafter referred to as an in-plane direction) at least when information is recorded. As a result, when a write magnetic field is generated by the magnetic head, the backing layer 6 induces the write magnetic field. As a result, a magnetic closed circuit is formed via the recording layer 10 between the magnetic head and the backing layer 6. Accordingly, the write magnetic field can be concentrated on the recording layer 10 to increase the strength and gradient of the magnetic field applied to the recording layer 10.

  Here, as shown in FIG. 1, the backing layer 6 is formed by alternately laminating the sub-lining film 5 and the nonmagnetic film 4. The sub-backing film 5 has the above-described magnetization in the in-plane direction of the backing layer 6. That is, the write magnetic field from the magnetic head is induced by the magnetization of the sub-backing film 5.

The sub-backing film 5 is made of a material that has magnetization in the in-plane direction at the signal recording temperature and whose magnetization becomes small at the signal reproduction temperature. In particular, it is preferable that the magnetization becomes substantially zero at the signal reproduction temperature. As such a material, a ferrimagnetic material can be used in which the net magnetization amount becomes zero (substantially zero) at the compensation temperature and the Curie temperature. Note that the above substantially zero means that when the ferrimagnetic material is used as the material of the sub-backing film 5, the sub-backing is sufficiently suppressed so that spike noise from the sub-backing film 5 is sufficiently suppressed during signal reproduction. it is that amount of magnetization film 5 approaches zero, the magnetization amount per unit of volume of ^{10emu / cc (emu / cm 3} ) or less, preferably indicates a zero.

  More specifically, a rare earth metal-transition metal alloy can be used as the material of the sub-backing film 5. In a ferrimagnetic material made of an alloy containing a rare earth metal element and a transition metal element, the magnetic characteristics change sharply with respect to temperature changes. Further, by changing the composition ratio between the rare earth metal element and the transition metal element, the compensation temperature and the Curie temperature of the ferrimagnetic material can be set to predetermined temperatures. In addition, the transition metal element in this specification refers to the thing except a rare earth metal element.

  In particular, at least one of gadolinium (Gd) and holmium (Ho) is used as the rare earth metal element, and at least one of the group consisting of iron (Fe), cobalt (Co), and nickel (Ni) as the transition metal element. An alloy using is preferable because it has a large magnetization in the in-plane direction at a high temperature region of 150 ° C. or higher. For example, a holmium-iron-cobalt (HoFeCo) alloy made of holmium, which is a rare earth metal, and iron and cobalt, which are transition metals, can be used. In that case, by adjusting the composition ratio of holmium, iron, and cobalt, the sub-backing film 5 has a compensation temperature that is substantially the same as the signal reproduction temperature, and is in the plane of the substrate 3 at the signal recording temperature. It is formed to have magnetization in the direction. In addition, the substantially same temperature means that when the compensation temperature of the ferrimagnetic material forming the sub-backing film 5 is set to the temperature, the amount of magnetization of the sub-backing film 5 is substantially zero at the signal reproduction temperature. Indicates that

  Here, as described above, the amount of magnetization of the ferrimagnetic material is substantially zero at the compensation temperature. For this reason, when the information recording medium 1 is reproduced, the sub-backing film 5 has a magnetization amount reduced to substantially zero. For this reason, leakage of leakage magnetic flux during signal reproduction from the backing layer 6 can be suppressed or completely eliminated. Thereby, spike noise during reproduction can be reduced or eliminated.

  Further, when recording is performed on the information recording medium 1, the sub-backing film 5 has magnetization in the in-plane direction. Therefore, as described above, the backing layer 6 can induce a write magnetic field generated by the magnetic head during signal recording. Thereby, a magnetic closed circuit can be formed between the magnetic head and the backing layer 6 via the recording layer 10. As a result, a magnetic field induced from the magnetic head to the backing layer 6 is applied to the recording layer 10. That is, the strength and gradient of the magnetic field applied to the recording layer 10 can be increased, and the magnetic field from the magnetic head can be efficiently concentrated and applied to the recording layer 10.

  The nonmagnetic film 4 is made of a nonmagnetic material. Its role is to magnetically separate each of the sub-backing films 5 constituting the backing layer 6 and stably maintain the magnetic anisotropy of each of the sub-backing films 5 in the in-plane direction of the substrate 3.

  As shown in FIG. 1, the nonmagnetic film 4 and the sub-backing film 5 are laminated alternately. As a result, the total thickness of the sub backing films can be increased while the thickness of each sub backing film 5 is kept thin. The in-plane magnetic anisotropy energy of the sub-backing film 5 depends on its shape. That is, the in-plane magnetic anisotropy energy can be increased by reducing the film thickness. Here, when the in-plane magnetic anisotropy energy of the sub-backing film 5 increases, the direction of magnetization of the sub-backing film 5 is determined in a certain direction. As a result, the backing layer 6 can induce the write magnetic field in a certain direction. Therefore, minute recording marks can be accurately and uniformly recorded on the recording layer 10.

  Further, each sub-backing film 5 is magnetically separated by the nonmagnetic film 4, so that it is not affected by the magnetic effects of the other sub-backing films 5. Therefore, the magnetization of each sub-backing film 5 is stably maintained in the in-plane direction of the substrate 3.

  Furthermore, it is generally reported that the thicker the backing layer 6 is, the more efficiently the magnetic field from the magnetic head can be concentrated and applied to the recording layer 10 (Hiroshi Wakamatsu et al., Journal of Applied Magnetics Society of Japan, Vol. 17, No. 5, 1993, p792-p796). Here, if the total thickness of the sub-lining film 5 is large as described above, the effect of inducing the magnetic field from the magnetic head to the backing layer 6 as in the case where the single-layer backing layer is thick. Have Thereby, the magnetic field from the magnetic head can be efficiently concentrated on the recording layer 10 and applied.

  Here, the average film thickness of the sub-backing film 5 which is the minimum necessary for stably maintaining the magnetic properties of each of the sub-backing films 5 is 5 nm. In order to increase the in-plane magnetic anisotropy energy of the secondary backing film 5 and form the backing layer 6 having the effects of the present invention, the average thickness of the secondary backing film 5 is 25 nm or less. preferable. Therefore, the average film thickness of each sub-backing film 5 is preferably 5 nm or more and 25 nm or less.

  The average film thickness of the nonmagnetic film 4 is preferably 1 nm or more. This is because each sub-backing film 5 constituting the backing layer 6 is magnetically separated, and the magnetization direction of each sub-backing film 5 is stably maintained in the in-plane direction of the substrate 3. Furthermore, the backing layer 6 can guide the recording magnetic field to the backing layer 6 more strongly as the distance from the magnetic head is shorter. Therefore, it is preferable that the distance between each sub-backing film 5 and the magnetic head is narrow. Accordingly, the nonmagnetic film 4 is preferably thin in order to reduce the distance. Specifically, in order to efficiently induce a magnetic field from the magnetic head to each sub-backing film 5, the film thickness of the nonmagnetic film 4 is preferably 3 nm or less. Therefore, the average film thickness of the nonmagnetic film 4 constituting the backing layer 6 is preferably 1 nm or more and 3 nm or less.

  The average film thickness is a value calculated by any of the following methods. That is, the surface of the layer can be ignored with respect to the thickness (film thickness) of the same material as that of the measurement target layer under the same conditions as the film formation condition of the measurement target layer. A film having a sufficient thickness is formed, and the film thickness of the formed layer is measured. Next, the film thickness (film formation rate) formed per unit time is calculated from the measured film thickness and film formation conditions. And using this film-forming speed | rate, the film thickness of the film | membrane of a measuring object is calculated | required from the film-forming time of a measuring object, and this is made into an average film thickness.

  In addition, after the information recording medium 1 is manufactured, the average film thickness can be measured by the following method. First, the information recording medium 1 is cut in a direction perpendicular to the surface of the substrate 3 to expose the laminated surface. By exposing the laminated surface, it is possible to observe the laminated state of each layer laminated in order from the substrate 3 side. This cross section is observed with a transmission electron microscope (TEM) or the like. In the information recording medium 1, a range of 1 μm is set in the in-plane direction, and a layer whose thickness is to be measured at a plurality of different locations within the 1 μm range is perpendicular to the surface of the substrate 3. Measure distance. Subsequently, an average value is calculated for the distances in the vertical direction measured at a plurality of locations within the range of 1 μm, and this average value is taken as an average film thickness.

(Description of recording layer 10)
The recording layer 10 holds information magnetically. Therefore, any recording information can be used as long as it can be held stably. That is, it is preferable that the magnetic anisotropy energy in the direction perpendicular to the surface of the substrate 3 is high and magnetized in the direction perpendicular to the surface of the substrate 3. Specifically, rare earth metals such as, but not limited to, terbium-iron-cobalt (TbFeCo) alloy, dysprosium-iron-cobalt (DyFeCo) alloy, or terbium-dysprosium-iron-cobalt (TbDyFeCo) alloy Transition metal alloy thin film, platinum (Pt), alloy thin film composed of at least one transition metal selected from manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), etc., platinum / Magnetic magnetic films such as cobalt (Pt / Co) and lead / cobalt (Pd / Co), or granular magnetism such as cobalt-chromium (CoCr) alloy and cobalt-chromium-platinum-silicon dioxide (CoCrPt-SiO2) alloy A thin film or the like can be used.

  Here, when a terbium-iron-cobalt (TbFeCo) alloy thin film, which is an amorphous medium and a perpendicular magnetic recording medium excellent in thermal stability, is used as in Example 1 described later, terbium-iron-cobalt (TbFeCo) is used. The alloy can be adjusted in magnetic properties by adjusting the composition of terbium (Tb), which is a rare earth metal, and iron (Fe), which is a transition metal, and cobalt (Co).

  That is, it is preferable to adjust the recording layer 10 so as to have a large magnetization at the signal reproduction temperature and to have a small holding force at the signal recording temperature. Thereby, at the time of signal reproduction, the information on the recording layer 10 can be reproduced with high sensitivity. Also, information can be recorded on the recording layer 10 by setting the coercive force of the recording layer 10 at the time of signal recording to be smaller than the write magnetic field from the magnetic head.

  When a crystalline material is used as the material of the recording layer 10, that is, at least one selected from platinum (Pt), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), and the like. Alloy thin films composed of the above transition metals, magnetic multilayer films such as platinum / cobalt (Pt / Co) and lead / cobalt (Pd / Co), and cobalt-chromium (CoCr) alloys and cobalt-chromium-platinum- When a granular magnetic thin film such as a silicon dioxide (CoCrPt—SiO 2) alloy is used, it is preferable to provide a seed layer (not shown) in order to improve the crystal orientation of the recording layer 10 and to suppress lattice defects. . As a material for the seed layer, for example, a titanium alloy such as titanium (Ti) or titanium-chromium (TiCr), or tantalum (Ta) can be used. Note that the material is not limited to the above material as long as it has an effect of improving the crystal orientation of the recording layer 10 and suppressing lattice defects.

(Description of protective layer 11)
The protective layer 11 is provided to protect the magnetic layer. That is, when the magnetic head and the information recording medium 1 are in contact, the magnetic layer of the information recording medium 1 is prevented from being scraped. The protective layer 11 is not particularly limited as long as it can protect the magnetic layer. For example, a carbon-based protective layer such as a carbon layer or a carbon nitride layer can be used.

(Description of the lubricating layer 12)
The lubrication layer 12 is for reducing friction at the time of contact between the magnetic head and the information recording medium 1 in the information recording or reproducing apparatus. As the material of the lubricating layer 12, a material conventionally used for a magnetic disk or the like can be used. For example, a fluorine-based lubricant, particularly a perfluoropolyoxyalkane (perfluoropolyether) -based lubricant can be used.

(Description of manufacturing method)
Next, a method for manufacturing the information recording medium 1 according to the first embodiment of the present invention will be described.

  First, the substrate 3 is placed in a chamber of a sputtering film forming apparatus (not shown), and the inside of the chamber is evacuated until a predetermined degree of vacuum is reached. Here, of the surface of the substrate 3, the surface on which each layer is laminated may be cleaned by a reverse sputtering method or the like. Thereafter, the sub-backing film 5 is formed on the substrate 3 using the magnetron sputtering method in the chamber. Next, the nonmagnetic film 4 is formed using the same method. Further, the backing layer 6 is formed by forming the sub-lining film 5 again using the same method.

  After forming the backing layer 6, the recording layer 10 is formed on the backing layer 6 using a magnetron sputtering method.

  After each layer is formed as described above, the protective layer 11 is formed using a DC magnetron sputtering method, and a lubricant is applied on the protective layer 11 using a dip coater to form the lubricating layer 12. To do. In addition, after forming the protective layer 11, tape burnishing may be performed and the lubricating layer 12 may be formed after that. The information recording medium 1 is manufactured by the above procedure.

  The backing layer 6 is formed with two sub-backing films 5, but the number of layers of the sub-lining film 5 is not limited to two. Any number of layers may be used as long as there are two or more layers. However, when the sub-backing film 5 has a plurality of layers, the non-magnetic film 4 must be provided between the sub-backing films 5.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to this.

[Example 1]
First, a glass substrate for a magnetic disk having a diameter of 2.5 inches was installed in a sputter deposition apparatus (not shown) as the substrate 3 in FIG. Then, the inside of the chamber (not shown) of the film forming apparatus provided with the substrate 3 was evacuated until the degree of vacuum was less than 3 × 10 ⁻⁵ Pa.

  Next, a holmium-iron-cobalt (HoFeCo) alloy thin film was formed on the substrate 3 as an auxiliary backing film 5 so as to have an average film thickness of 25 nm. Specifically, using magnetron sputtering, a film was formed by co-sputtering using a ternary target of holmium (Ho), iron (Fe), and cobalt (Co). As sputtering conditions, the sputtering gas pressure is 0.2 Pa, the sputtering input power is DC voltage (DC), holmium (Ho) is 383 W, iron (Fe) is 200 W, cobalt (Co) is 632 W, and sputtering is performed. Argon (Ar) gas was used as the gas. As a result of measuring the composition of the formed sub-backing film 5 with a fluorescent X-ray analyzer (XRF), the composition ratio of each element is the element composition (at%), holmium (Ho) is 23.4 at%, Iron (Fe) was 17.3 at% and cobalt (Co) was 59.4 at%.

  Next, as the nonmagnetic film 4, an aluminum film was formed to an average film thickness of 3 nm by using magnetron sputtering.

  Next, a holmium-iron-cobalt (HoFeCo) alloy thin film was again formed as the sub-backing film 5 under the same conditions as those for forming the sub-backing film 5 so that the average film thickness was 25 nm.

  Next, a terbium-iron-cobalt (TbFeCo) alloy thin film was formed as the recording layer 10. Specifically, three targets of terbium (Tb), iron (Fe), and cobalt (Co) were formed by co-sputtering using a magnetron sputtering method. The sputtering conditions are as follows. That is, the sputtering gas pressure was 0.2 Pa. Sputtering input power was direct current voltage (DC), terbium (Tb) was 72 W, iron (Fe) was 200 W, and cobalt (Co) was 39 W. Argon (Ar) gas was used as the sputtering gas. As a result of measuring the composition of the recording layer 10 formed using a fluorescent X-ray analyzer, the composition ratio of each element is the element composition (at%), terbium (Tb) is 17.0 at%, and iron (Fe). Was 68.9 at% and cobalt (Co) was 14.1 at%.

  Next, an amorphous carbon (a-C) film was formed as the protective layer 11 by DC magnetron sputtering so that the average film thickness was 10 nm. The sputtering conditions are as follows. The sputtering gas pressure was 1.0 Pa. The sputtering input power was a DC power of 300 W at a DC voltage (DC). Argon (Ar) gas was used as the sputtering gas.

  Next, a perfluoropolyoxyalkane-based lubricant was applied to the interface of the protective layer 11 with a dip coater. As a result, a liquid lubricating film having a thickness of 0.8 nm was formed as the lubricating layer 12.

Here, FIG. 3 is a graph showing the magnetic properties of the terbium-iron-cobalt (TbFeCo) alloy thin film forming the recording layer 10. The vertical axis in FIG. 3 represents the remanent magnetization emu / cc (emu / cm ³ ) per unit volume of the terbium-iron-cobalt (TbFeCo) alloy thin film. The horizontal axis is absolute temperature (Kelvin). For the magnetization measurement, the temperature dependence of the residual magnetization was measured using a VSM (Sample Vibration Type Magnetometer) (not shown).

  In this embodiment, the signal reproduction temperature was set to room temperature (about 30 ° C.) and the signal recording temperature was set to about 240 ° C. As shown in FIG. 3, the recording layer 10 of the information recording medium 1 according to the present embodiment has a large magnetization at room temperature, which is a signal reproduction temperature. Therefore, information on the recording layer 10 can be reproduced with high sensitivity during signal reproduction. Further, as shown in the figure, the recording layer 10 has a small residual magnetization in the vicinity of 240 ° C. which is the signal recording temperature. This indicates that the recording layer 10 has a small coercive force during signal recording. Thus, since the coercive force of the recording layer 10 is small, the write magnetic field from the magnetic head can be easily made larger than the coercive force of the recording layer 10. That is, information can be easily recorded on the recording layer 10.

  Next, the magnetic properties of the backing layer 6 were measured using a sample vibration type magnetometer (VSM).

FIG. 4 is a graph showing the amount of magnetization of the backing layer 6 in the in-plane direction of the substrate 3 at the signal recording temperature (about 240 ° C.). FIG. 5 is a graph showing the amount of magnetization of the backing layer 6 in the in-plane direction of the substrate 3 at the signal reproduction temperature (about 30 ° C.). Each vertical axis represents the amount of magnetization emu / cc (emu / cm ³ ) per unit volume. The horizontal axis represents the applied magnetic field Oe applied from the outside.

  As shown in FIG. 4, at the signal recording temperature (about 240 ° C.), the backing layer 6 has magnetization in the in-plane direction of the substrate 3. Further, as shown in FIG. 5, at the signal reproduction temperature (about 30 ° C.), the magnetization amount of the backing layer 6 became zero.

  As shown in the above measurement results, when the information signal recorded on the recording layer 10 of the information recording medium 1 is reproduced, the magnetization of the backing layer 6 becomes zero. Therefore, leakage of leakage magnetic flux from the backing layer 6 during signal reproduction is suppressed, and spike noise is suppressed.

  Further, when the information signal is recorded on the recording layer 10, the backing layer 6 has magnetization in a direction perpendicular to the stacking direction. Therefore, when recording an information signal on the recording layer 10 of the information recording medium 1, a magnetic closed circuit is formed between the magnetic head and the backing layer 6 in the information reproducing apparatus or information recording / reproducing apparatus via the recording layer 10. Is done. Accordingly, a magnetic field induced from the magnetic head to the backing layer 6 is applied to the recording layer 10. Thereby, since the intensity and gradient of the magnetic field applied to the recording layer 10 can be increased, the magnetic field from the magnetic head can be efficiently concentrated on the recording layer 10 and applied.

Next, the in-plane magnetic anisotropy energy of the backing layer 6 (hereinafter referred to as backing layer A) of the information recording medium 1 was measured using a torque method. At this time, as a comparative control, a single-layer backing film (hereinafter referred to as backing film B) in which a holmium-iron-cobalt (HoFeCo) alloy thin film was formed to an average film thickness of 50 nm was also measured. The measurement temperature is 240 ° C., which is the signal recording temperature. As a result, the magnetic anisotropy constants of the backing layer A and the backing layer B in the in-plane direction of the substrate 3 determined by the torque method are 3.8 × 10 ⁵ erg / cc (erg / cm ³ ), 1. 2 × 10 ⁵ erg / cc (erg / cm ³ ), and the backing layer A had larger in-plane magnetic anisotropy energy.

  As shown in the above measurement results, the backing layer 6 of the present invention has larger in-plane magnetic anisotropy energy than the backing film formed as a single layer. This is due to the following reason.

  That is, the backing layer 6 of this example is formed by laminating a holmium-iron-cobalt (HoFeCo) alloy thin film (25 nm), an aluminum film (3 nm), and a holmium-iron-cobalt (HoFeCo) alloy thin film (25 nm) in this order. Become. Usually, when a holmium-iron-cobalt (HoFeCo) alloy thin film is used as the backing layer 6, it is preferable to have a film thickness of 50 nm or more. However, by increasing the film thickness, the magnetic anisotropy energy in the in-plane direction of the backing layer 6 depending on the film shape is reduced. Here, as described above, the backing layer 6 of the information recording medium 1 of the present embodiment has a structure in which the sub backing film 5 and the nonmagnetic film 4 are alternately laminated. Thus, while the total thickness of the sub-backing film 5 is 50 nm, the thickness of each of the sub-backing films 5 is reduced (25 nm) to increase the in-plane magnetic anisotropy energy.

  Next, the information recording medium 1 was mounted on an information recording / reproducing apparatus, and a recording / reproducing evaluation was performed.

  The information recording medium 1 in this embodiment is referred to as an information recording medium A. An information recording medium prepared by the same procedure as in this example is used as the information recording medium B except that the backing layer B is used instead of the backing layer A as the backing layer 6. The information recording medium A and the information recording medium B were mounted on an information recording / reproducing apparatus.

  The recording / reproduction evaluation was performed according to the following procedure. First, recording is performed under the same conditions by the recording head of the information recording / reproducing apparatus. Next, the reproduction signal waveform is read by the reproducing head of the information recording / reproducing apparatus. FIG. 6 is a graph showing the results of performing the above on the information recording medium A and the information recording medium B. The solid line in the figure shows the reproduction signal waveform of the information recording medium A. A broken line indicates a reproduction signal waveform of the information recording medium B. The vertical axis represents the reproduction signal output [V]. The horizontal axis represents time [sec].

  Here, the magnetization transition lengths of the information recording medium A and the information recording medium B are shown in FIG. 6 as the magnetization transition length A and the magnetization transition length B, respectively. The magnetization transition length is a transition width when the magnetization direction recorded in the information recording medium changes. When the magnetization transition length is small, a large amount of magnetization information can be recorded per unit length of the recording track. Therefore, the recording density per unit area in the information recording medium 1 can be increased.

  As shown in FIG. 6, the magnetization transition length A in the information recording medium A is smaller than the magnetization transition width B in the information recording medium B. Therefore, higher density recording is possible.

  This is due to the following reason. That is, in the information recording medium B, as described above, the in-plane magnetic anisotropy energy of the backing layer 6 is low. Therefore, the magnetization of the backing layer 6 also has a degree of freedom in the direction perpendicular to the substrate 3. Therefore, the recording magnetic field guided from the recording head to the backing layer 6 is disturbed. Therefore, the magnetization transition length is increased. As a result, it is difficult to write a desired minute recording mark accurately and uniformly.

  On the other hand, the information recording medium A has a high in-plane magnetic anisotropy energy of the backing layer 6. Therefore, the recording magnetic field from the magnetic head can be abruptly guided to the backing layer 6. Therefore, the magnetization transition length is reduced.

  As described above, according to the configuration of the present embodiment, the in-plane magnetic anisotropy energy of the backing layer 6 can be increased by reducing the average thickness of the sub-lining film 5. Furthermore, the total film thickness obtained by adding the film thicknesses of the sub-backing films 5 is thick. Therefore, the induction effect of the recording magnetic field on the backing layer 6 is almost the same as when a single backing layer is formed with a film thickness equivalent to the total film thickness. As a result, the recording magnetic field induced in the backing layer 6 is induced in a certain direction, and minute recording marks can be recorded accurately and uniformly.

  In this embodiment, the signal reproduction temperature is room temperature (about 30 ° C.) and the signal recording temperature is about 240 ° C., but both are not limited to the above temperature. However, when the temperature is changed, the magnetic properties of the recording layer 10 and the auxiliary backing film 5 constituting the backing layer 6 are adjusted. For example, when the signal regeneration temperature is set to around 90 ° C., the sub-lining film 5 is adjusted to have a compensation temperature around 90 ° C. Further, the magnetic characteristics are adjusted so as to have a large magnetization in the in-plane direction of the substrate 3 near the signal recording temperature. That is, the sub-backing film 5 does not generate a leakage magnetic field at the time of signal reproduction, and sets magnetic characteristics so as to have a large magnetization in the in-plane direction of the substrate 3 at the time of signal recording. Moreover, the recording layer 10 generates a large leakage magnetic field during signal reproduction, and sets the magnetic characteristics so that the coercive force is smaller than the recording magnetic field from the magnetic head during signal recording.

[Second Embodiment]
A second embodiment of the present invention will be described below.

(Explanation of membrane structure)
FIG. 2 is a cross-sectional view showing a film configuration of the information recording medium 2 according to another embodiment. As shown in the figure, the information recording medium 2 includes a substrate 3, a backing layer 6 in which a sub-backing film 5 and a nonmagnetic film 4 are alternately laminated, a dielectric layer 7, and an uneven layer 8. The layer 9, the recording layer 10, the protective layer 11, and the lubricating layer 12 are laminated in this order.

  Here, in the information recording medium 2 having the above-described configuration, the layers other than the nonmagnetic intermediate layer 9 follow the description described in the first embodiment. The description after the film formation of the information recording medium 2 also follows the description described in the first embodiment. Hereinafter, the nonmagnetic intermediate layer 9 will be described.

(Description of Nonmagnetic Intermediate Layer 9)
As shown in FIG. 2, the nonmagnetic intermediate layer 9 is disposed between the backing layer 6 and the recording layer 10 and includes a dielectric layer 7 and an uneven layer 8. The nonmagnetic intermediate layer 9 prevents magnetic exchange interaction between the backing layer 6 and the recording layer 10. Therefore, it is possible to prevent the magnetization direction of the recording layer 10 from being affected by the magnetization direction of the backing layer 6 during signal recording on the information recording medium 2. Therefore, good signal recording can be realized.

  Further, the nonmagnetic intermediate layer 9 has an uneven shape at the interface with the recording layer 10. This is intended to induce a pinning effect that hinders the movement of the domain wall in the recording layer 10. More specifically, the nonmagnetic intermediate layer 9 has a minute uneven shape at the interface with the recording layer 10 formed on the nonmagnetic intermediate layer 9. This uneven shape serves as a domain wall binding site (pinning site) that prevents the domain wall from moving in the recording layer 10. That is, the concavo-convex shape of the nonmagnetic intermediate layer 9 divides the magnetic domain formed in the recording layer 10 and limits it within each concave portion or each convex portion forming the concavo-convex shape. Therefore, the moving distance of the domain wall that is the boundary between the magnetic domains is limited depending on the diameter of the concave portion or the convex portion forming the concave and convex shape. That is, when the information signal is recorded on the recording layer 10, the movement of the domain wall can be limited to a short distance as compared with the case where the uneven shape is not present. Thereby, a minute recording bit can be stably formed in the recording layer 10. Therefore, high-density recording can be realized in the information recording medium 2. Further, when reproducing the signal recorded on the recording layer 10, since the movement of the domain wall of the recording layer 10 is limited, good signal reproduction characteristics can be obtained when reproducing the signal of the information recording medium 2.

  Here, the upper limit of the average film thickness of the nonmagnetic intermediate layer 9 is 5 nm. Furthermore, the average film thickness is preferably 4 nm or less, and more preferably 3 nm or less. Moreover, the lower limit of the average film thickness is not particularly limited. However, the average film thickness is preferably 1 nm or more, and more preferably 1.2 nm or more.

  When the average film thickness exceeds 5 nm, the distance between the magnetic head of the recording / reproducing apparatus, which will be described later, and the backing layer 6 increases during signal recording on the recording layer 10 of the information recording medium 2, and the write magnetic field from the magnetic head is reduced. It tends to be difficult to guide to the backing layer 6. As a result, the strength and gradient of the write magnetic field applied to the recording layer 10 tend to decrease, which makes it difficult to improve the recording resolution. Another problem is that the thickness of the nonmagnetic intermediate layer 9 tends to increase and the thickness of the information recording medium 2 tends to increase. On the other hand, if the average film thickness is less than 1 nm, it tends to be difficult to prevent the occurrence of magnetic exchange interaction between the backing layer 6 and the recording layer 10, which is not preferable.

  The average film thickness is a value calculated by any of the following methods. That is, the surface of the layer can be ignored with respect to the thickness (film thickness) of the same material as that of the measurement target layer under the same conditions as the film formation conditions of the measurement target layer. A film having a sufficient thickness is formed, and the film thickness of the formed layer is measured. Next, the film thickness (film formation rate) formed per unit time is calculated from the measured film thickness and film formation conditions. And using this film-forming speed | rate, the film thickness of the film | membrane of a measuring object is calculated | required from the film-forming time of a measuring object, and this is made into an average film thickness.

  Further, after the information recording medium 2 is manufactured, the average film thickness can be measured by the following method. First, the magnetic disk is cut in a direction perpendicular to the surface of the substrate 3, and the laminated surface of each layer, which is the cut surface, is observed with a transmission electron microscope (TEM) or the like. In the information recording medium 2, a range of 1 μm is set in the in-plane direction, and a layer whose thickness is to be measured at a plurality of different locations within the 1 μm range is perpendicular to the surface of the substrate 3. Measure distance. Subsequently, an average value is calculated for the distances in the vertical direction measured at a plurality of locations within the range of 1 μm, and this average value is taken as an average film thickness.

  Next, the dielectric layer 7 and the uneven layer 8 included in the nonmagnetic intermediate layer 9 will be described.

  The concavo-convex layer 8 forms the concavo-convex shape of the nonmagnetic intermediate layer 9 and has a function of inducing a pinning effect. The uneven layer 8 may be a layer made of a nonmagnetic metal, and for example, aluminum, zinc, or the like can be used. Among these, aluminum can increase the average surface roughness Ra as described later. Further, when aluminum is used for the concave / convex layer 8, it is easy to be chemically bonded by forming a compound with the metal film forming the recording layer 10, and the concave / convex shape is easily maintained. Therefore, a high pinning effect can be expected. Therefore, the concavo-convex layer 8 is preferably formed using aluminum.

  Moreover, as for the said uneven | corrugated layer 8, the upper limit of the average film thickness measured by an above-described method is 3 nm or less. Further, the average film thickness is preferably 2.5 nm or less, and more preferably 2 nm or less. Moreover, the lower limit of the average film thickness is not particularly limited. However, the average film thickness is preferably 1 nm or more, and more preferably 1.5 nm or more.

  If the average film thickness exceeds 3 nm, the thickness of the information recording medium 2 increases, which is not preferable. On the other hand, when the average film thickness is less than 1 nm, the average surface roughness Ra of the concavo-convex structure at the interface between the concavo-convex layer 8 and the recording layer 10 becomes small, and the domain wall binding site (which prevents the domain wall in the recording layer 10 from moving) The effect as a pinning site is difficult to occur, which is not preferable.

  Furthermore, the average surface roughness Ra of the uneven layer 8 is preferably larger than the average surface roughness Ra of the backing layer 6. Specifically, the upper limit value of the average surface roughness Ra of the uneven layer 8 is 1.5 nm. Furthermore, the average surface roughness Ra is preferably 1.3 nm or less, and more preferably 1.1 nm or less. Further, the lower limit value of the average surface roughness Ra is not particularly limited as long as it is larger than the average surface roughness Ra of the backing layer 6. However, the average surface roughness Ra is preferably 0.6 nm or more, and more preferably 0.8 nm or more.

  When the average surface roughness Ra exceeds 1.5 nm, the diameter of the protrusions formed on the uneven layer 8 increases. That is, it becomes difficult to form a minute uneven shape in the recording layer 10. Therefore, the moving distance of the domain wall is not limited to be short. Therefore, it becomes difficult to form a minute recording bit in the recording layer 10. From the above, in order to perform high density recording while maintaining sufficient signal quality, the average surface roughness Ra is preferably 1.5 nm or less. On the other hand, when the average surface roughness Ra is less than 0.6 nm, since the average surface roughness Ra of the concavo-convex structure at the interface between the concavo-convex layer 8 and the recording layer 10 is small, the domain wall in the recording layer 10 moves. Since the effect as a domain wall binding site (pinning site) to be hindered is difficult to occur, it is not preferable.

  Here, the average surface roughness Ra is based on the definition of JIS B 0601-1982. That is, it represents the centerline average roughness regarding the amplitude of fine irregularities. The average surface roughness Ra can be measured by the following method after the information recording medium 2 is manufactured. That is, the information recording medium 2 is cut in a direction perpendicular to the surface of the substrate 3, and the laminated surface of each layer that is the cut surface is observed by the TEM or the like. Then, the uneven shape at the interface between the uneven layer 8 and the recording layer 10 may be measured to calculate the average surface roughness.

  Further, the upper limit of the diameter of the convex portion formed on the concave / convex layer 8 on the surface of the concave / convex layer 8, that is, the interface between the concave / convex layer 8 and the recording layer 10 is 50 nm. Furthermore, the diameter of the convex portion is preferably 45 nm or less, and more preferably 40 nm or less. The lower limit value of the diameter of the convex portion is not particularly limited. However, the diameter of the convex portion is preferably 15 nm or more, and more preferably 20 nm or more.

  If the diameter of the convex portion is 50 nm or more, it is difficult to form a minute uneven shape in the recording layer 10 and it is difficult to suppress the moving distance of the domain wall in the recording layer 10. It is not preferable. Further, the small diameter of the convex portion means that the diameter of the concave portion formed on the surface of the concave / convex layer 8 is large, and similarly, it becomes difficult to form a fine concave / convex shape in the recording layer 10. It is not preferable.

  Here, the convex portion refers to a portion that is higher from the bottom portion along the stacking direction of the layers of the information recording medium 2 with respect to the bottom portion of the concave portion. Moreover, the diameter of the said convex part approximates the convex part formed in the uneven | corrugated layer 8 using a cone, and calculated | required the average value of the diameter of the bottom face. However, this does not limit the shape of the convex portion to a conical shape. Various shapes can be considered as the shape of the convex portion. For example, a pituitary shape in which the bottom surface is a circle, an ellipse, or a distorted circle, and one vertex exists.

  The dielectric layer 7 may be formed as a film on the backing layer 6 as described above to form a layer, or a compound forming the dielectric layer 7 on the backing layer 6 May be arranged in such a manner as to be scattered as particles. That is, the dielectric layer 7 may be a layer in which the above-described compounds such as nitrides and oxides are scattered on the backing layer 6 and distributed in an island shape.

  Further, the concavo-convex layer 8 may be formed in a film shape and have a concavo-convex shape, or may be arranged so as to be scattered on the dielectric layer 7 to have a concavo-convex shape. That is, the concavo-convex layer 8 may be a layer in which the nonmagnetic metal used for the concavo-convex layer 8 is made into particles and dispersed on the dielectric layer 7 so as to be distributed in an island shape. .

  When at least one of the dielectric layer 7 and the concavo-convex layer 8 is formed in an island shape, the lower limit value of the average surface roughness Ra depends on the average surface roughness of each layer disposed below the concavo-convex layer 8. It will be. Therefore, it is difficult to specify the lower limit value of the average surface roughness Ra of the uneven layer 8. However, the average surface roughness of the substrate 3 is usually about 0.48 nm, the average surface roughness of the backing layer 6 using the HoFeCo alloy is about 0.38 nm, and when the uneven layer 8 is made of aluminum, Since the atomic radius of aluminum is 1.43 mm (0.143 nm), the lower limit value of the average surface roughness Ra of the uneven layer 8 is considered to be about 0.6 nm.

  The dielectric layer 7 is provided so as to be in contact with the backing layer 6 and has a function of facilitating the formation of the concave / convex layer 8 thereon. The dielectric layer 7 may be a layer made of a dielectric. Specifically, at least one of nitride and oxide may be used. In general, a metal film formed on a nitride or an oxide hardly causes diffusion. Therefore, the metal film is not formed uniformly, but is formed to have an uneven shape. By utilizing this property, it is possible to easily form the nonmagnetic intermediate layer 9 having an uneven shape. In the present embodiment, the dielectric layer 7 is formed of at least one of nitride and oxide, and the uneven layer 8 of the metal film is formed on the dielectric layer 7. Therefore, the uneven layer 8 of the nonmagnetic intermediate layer 9 is disposed so as to be in contact with the recording layer 10.

  Here, when the dielectric layer 7 is formed of nitride, the nitride is not particularly limited. For example, one or two kinds selected from silicon nitride (SiN), aluminum nitride, titanium nitride, and the like are used. The above nitrides can be used. In addition, when the dielectric layer 7 is formed of an oxide, the oxide is not particularly limited. For example, the oxide is selected from silicon oxide, aluminum oxide, titanium oxide, silver oxide, platinum oxide, and the like. Alternatively, two or more kinds of oxides can be used.

  In addition, the upper limit of the average film thickness of the dielectric layer 7 measured by the above method is 2 nm. Further, the average film thickness is preferably 1.5 nm or less, and more preferably 1 nm or less. Moreover, the lower limit of the average film thickness is not particularly limited. However, the average film thickness is preferably 0.4 nm or more, and more preferably 0.6 nm or more.

  If the average film thickness exceeds 2 nm, the film thickness of the information recording medium 2 is increased, which is not preferable. On the other hand, when the average film thickness is less than 0.4 nm, it is difficult to uniformly form the dielectric layer 7 on the backing layer 6. Therefore, when the uneven layer 8 is formed on the heterogeneous dielectric layer 7, the uneven structure at the interface between the uneven layer 8 and the recording layer 10 varies, and the characteristics of the recording layer 10 are controlled. It is not preferable.

  When the surface of the backing layer 6 is nitrided or oxidized by plasma etching or the like, the nitrided or oxidized backing layer 6 surface can also be used as the dielectric layer 7.

(Description of manufacturing method)
The manufacturing method of the information recording medium 2 according to the present embodiment is the first except that the nonmagnetic intermediate layer 9 including the dielectric layer 7 and the concavo-convex layer 8 is provided between the backing layer 6 and the recording layer 10. This is the same as the manufacturing method of the information recording medium 2 according to the embodiment. The nonmagnetic intermediate layer 9 is formed as follows.

  First, the backing layer 6 is formed by the same procedure as in Example 1, and then the dielectric layer 7 is formed by reactive sputtering. Next, the uneven layer 8 is formed on the dielectric layer 7 by using a magnetron sputtering method. The nonmagnetic intermediate film 9 is formed by the above procedure.

(Concavity and convexity observation on the surface of the concave and convex layer 8)
Hereinafter, the surface shape of the uneven layer 8, will be described in more detail in the examples, the present invention is not limited thereto.

[Example 2]
On the substrate 3, a holmium-iron-cobalt (HoFeCo) alloy thin film (25 nm), an aluminum film (3 nm), and a holmium-iron-cobalt (HoFeCo) alloy thin film (25 nm) were laminated in this order to form a backing layer 6. On top of that, an aluminum nitride (AlN) film (2 nm) was laminated to form a dielectric layer 7. An uneven layer 8 was formed by laminating an aluminum (Al) film (3 nm) thereon. And the uneven | corrugated layer 8 surface shape was observed with the atomic force microscope (AFM), and the average surface roughness (Ra) at that time was measured. Details will be described below.

First, a glass substrate was used as the substrate 3, and this was installed in a sputtering film forming apparatus (not shown). Then, the chamber (not shown) of the sputter deposition apparatus was evacuated until the degree of vacuum was less than 3 × 10 ⁻⁵ Pa.

  Next, a holmium-iron-cobalt (HoFeCo) alloy thin film was formed on the substrate 3 as the sub-backing film 5 constituting the backing layer 6. Specifically, a magnetron sputtering method was used to form a film by co-sputtering using a ternary target of holmium (Ho), iron (Fe), and cobalt (Co) so that the average film thickness was 25 nm. As sputtering conditions, the sputtering gas pressure is 0.2 Pa, the sputtering input power is DC voltage (DC), holmium (Ho) is 383 W, iron (Fe) is 200 W, cobalt (Co) is 632 W, and sputtering is performed. Argon (Ar) gas was used as the gas. As a result of measuring the composition of the formed sub-backing film 5 with a fluorescent X-ray analyzer (XRF), the composition ratio of each element is the element composition (at%), holmium (Ho) is 23.4 at%, Iron (Fe) was 17.3 at% and cobalt (Co) was 59.4 at%.

  After the sub-backing film 5 was formed, an aluminum film was formed as the non-magnetic film 4 constituting the backing layer 6 using a magnetron sputtering method so as to have an average film thickness of 3 nm.

  After the nonmagnetic film 4, a holmium-iron-cobalt (HoFeCo) alloy thin film was formed again so that the average film thickness was 25 nm under the same conditions as those for forming the sub-backing film 5. Thereby, the backing layer 6 was formed.

  After forming the backing layer 6, an AlN film was formed as the dielectric layer 7. Specifically, the film was formed by a reactive sputtering method so as to have an average film thickness of 2 nm. As the sputtering conditions, the sputtering gas pressure was 0.08 Pa, the sputtering input power was 2 kW at the high frequency voltage (RF), and argon (Ar) and nitrogen gas (N2) were used as the sputtering gas.

  After the dielectric layer 7 was formed, an aluminum film was formed as the concavo-convex layer 8 using a magnetron sputtering method so as to have an average film thickness of 3 nm.

  As described above, after forming the uneven layer 8 by the same procedure as that for producing the information recording medium 2, a sample (hereinafter referred to as sample A) was taken out from the chamber. And the surface shape of the uneven | corrugated layer 8 (aluminum film) was observed with the atomic force microscope (AFM). FIG. 7 is a perspective view showing an AFM observation image of sample A. FIG. As shown in the figure, the surface of the aluminum film has a very large surface roughness. When measured by the surface roughness measurement method described above, the average surface roughness (Ra) was 1.0 nm.

[ Example 3 ]
As a comparative sample, the same film formation conditions as in Sample A were used. On the glass substrate 3, a holmium-iron-cobalt (HoFeCo) alloy thin film (25 nm), an aluminum film (3 nm), and a HoFeCo alloy thin film (25 nm) were sequentially formed. A filmed sample (hereinafter referred to as Sample B) was prepared.

  Thereafter, the surface shape of the holmium-iron-cobalt (HoFeCo) film was observed with an atomic force microscope (AFM). FIG. 8 is a perspective view showing an AFM observation image of sample B. FIG. As shown in the figure, it can be seen that the average surface roughness (Ra) of the surface of the backing layer 6 (HoFeCo film) is very small and has a flat surface shape. When the surface roughness was measured by the method described above, it was 0.38 nm.

[ Example 4 ]
Using the same film formation conditions as in Sample A above, a holmium-iron-cobalt (HoFeCo) alloy thin film (25 nm), an aluminum film (3 nm), and a holmium-iron-cobalt (HoFeCo) alloy thin film (25 nm) on the glass substrate 3. Then, a sample (hereinafter referred to as sample C) in which an aluminum film was formed in the order of 5 nm was prepared.

  Thereafter, the surface shape of the aluminum film was observed by AFM. FIG. 9 is a perspective view showing an AFM observation image of sample C. FIG. As shown in the figure, the surface on which the Al film (5 nm) is formed on the backing layer 6 is also flat and the surface roughness is small. When the surface roughness was measured by the method described above, it was 0.43 nm.

  As shown in the above results, the aluminum nitride (AlN) film as the dielectric layer 7 and the aluminum (Al) film as the concavo-convex layer 8 are sequentially laminated on the backing layer 6 as in the present embodiment. The concavo-convex layer 8 having a surface roughness larger than that of the backing layer 6 can be formed.

  The present invention has been specifically described above based on the embodiments. However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the invention. It is.

  The present invention can be used for an information recording medium that records and reproduces information by magnetic action, and can be suitably used particularly for an information recording medium of a perpendicular magnetic recording system.

It is sectional drawing which shows the structure of the information recording medium which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the structure of the information recording medium which concerns on the 2nd Embodiment of this invention. It is a graph which shows the magnetic characteristic of the recording layer of the information recording medium which concerns on the 1st Embodiment of this invention. It is a graph which shows the magnetic characteristic in the signal recording temperature of the backing layer of the information recording medium which concerns on the 1st Embodiment of this invention. It is a graph which shows the magnetic characteristic in the signal reproduction temperature of the backing layer of the information recording medium which concerns on the 1st Embodiment of this invention. It is a graph showing the waveform of the reproduction signal of the information recording medium which concerns on the 1st Embodiment of this invention, and another information recording medium. It is an atomic force microscope image which shows the surface shape of the sample A which concerns on the 2nd Embodiment of this invention. It is an atomic force microscope image which shows the surface shape of the sample B which concerns on the 2nd Embodiment of this invention. It is an atomic force microscope image which shows the surface shape of the sample C which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

1, 2 Information recording medium 3 Substrate 4 Nonmagnetic film 5 Sub-backing film 6 Backing layer 7 Dielectric layer 8 Concavity and convexity layer 9 Nonmagnetic intermediate layer 10 Recording layer 11 Protective layer 12 Lubricating layer

Claims (11)

A recording layer on which information signals are magnetically recorded;
A backing layer for concentrating the magnetic field used for recording the information signal on the recording layer;
The backing layer is provided below the recording layer, and is formed by alternately laminating a plurality of sub backing films and at least one nonmagnetic film made of a nonmagnetic material,
The secondary backing film has a magnetization in a direction perpendicular to the stacking direction at the recording temperature of the information signal, and has a compensation temperature that is substantially the same temperature as the reproduction temperature of the information signal. Is formed by
The ferrimagnetic material is an alloy containing at least one element selected from rare earth metal elements and at least one element selected from transition metal elements,
An information recording medium of a perpendicular magnetic recording system, wherein the sub-backing film has an average film thickness of 5 nm to 25 nm . The rare earth metal element, the information recording medium of the perpendicular magnetic recording system according to claim 1, characterized in that at least one of gadolinium and holmium. The transition metal element, iron, cobalt, and the information recording medium of the perpendicular magnetic recording system according to claim 1 or 2, characterized in that at least one selected from the group consisting of nickel. The perpendicular magnetic recording type information recording medium according to any one of claims 1 to 3, wherein an average film thickness of the nonmagnetic film is 1 nm or more and 3 nm or less. The perpendicular magnetic recording type information recording medium according to any one of claims 1 to 4, further comprising a nonmagnetic intermediate layer made of a nonmagnetic material between the backing layer and the recording layer. . The average thickness of the nonmagnetic intermediate layer, the information recording medium of the perpendicular magnetic recording system according to claim 5, characterized in that at 1nm or 5nm or less. The nonmagnetic intermediate layer includes a dielectric layer formed of a dielectric and an uneven layer formed on the dielectric layer,
7. The perpendicular magnetic recording type information recording medium according to claim 5 , wherein the concavo-convex layer has a concavo-convex shape at an interface with the recording layer. 8. The perpendicular magnetic recording type information recording medium according to claim 7 , wherein the dielectric layer is formed of at least one of a nitride and an oxide. 9. The perpendicular magnetic recording type information recording medium according to claim 7 , wherein the uneven layer is made of aluminum. The perpendicular magnetic recording type information recording medium according to any one of claims 7 to 9, wherein an average film thickness of the dielectric layer is 0.4 nm or more and 2 nm or less. The perpendicular magnetic recording type information recording medium according to any one of claims 7 to 10, wherein an average film thickness of the concavo-convex layer is 1 nm or more and 3 nm or less.