JP3090891B2 - Thermomagnetic recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermomagnetic recording medium. 2. Description of the Related Art In a thermomagnetic recording method for recording information on a recording medium from which information bits (magnetic domains) are read by magneto-optical interaction, a recording medium having a magnetic thin film made of a perpendicular magnetic film is used. On the other hand, a so-called initialization has been performed in which the direction of the magnetization is previously aligned in one direction perpendicular to the film surface,
By forming a bit with perpendicular magnetization opposite to this magnetization direction by local heating such as laser beam irradiation,
It records the coded information. In this thermomagnetic recording method, prior to rewriting of information, a process of erasing recorded information (corresponding to the above initialization), that is, a time for erasing is required, and a high transfer rate is required. Recording cannot be realized. On the other hand, various recording methods based on the overwrite method in which the time for the independent erasing process is not required have been proposed. Promising methods among the overwrite type thermomagnetic recording methods include, for example, an external magnetic field modulation method for a medium and a two-head method in which an erasing head is provided in addition to a recording head. ing. The external magnetic field modulation method refers to irradiation of a heating beam to an amorphous ferrimagnetic thin-film recording medium having an easy axis of magnetization perpendicular to the film surface, as described in, for example, Japanese Patent Application No. 60-48806. Recording is performed by applying a magnetic field having a polarity corresponding to the state of the input digital signal current to the area. In order to perform high-speed recording at a high information transfer rate by the above-described external magnetic field modulation method, an electromagnet operating in, for example, the order of MHz is required. It is difficult to manufacture such a device, and even if it can be manufactured, there is a problem that power consumption and heat generation are large and impractical. In the two-head method,
An extra head is required, and the two heads must be set apart, placing a heavy burden on the drive system.
It has problems such as poor economy and not suitable for mass production. According to the present invention, rewriting, that is, overwriting can be easily performed only by switching control of a heating temperature of a medium by a laser beam or the like, and the above-mentioned problems have been solved. Incidentally, the present applicant has previously described a thermomagnetic recording method for solving such a problem, as disclosed in Japanese Patent Application No. 61-1949.
No. 61 and Japanese Patent Application No. 61-194962. The thermomagnetic recording methods proposed in these applications use a thermomagnetic recording medium having a laminated structure of first and second rare earth-transition metal magnetic thin films, and apply a first first external magnetic field under a required first external magnetic field. almost a first heating condition for heating the first temperature T ₁ of the inversion does not occur in the sub-lattice magnetization of the Curie temperature T _C1 and not more than the second magnetic thin film, the temperature T _C1 and not more than the second magnetic thin film A second heating state in which the magnetic thin film is heated to a _second temperature T ₂ sufficient to reverse the sublattice magnetization is switched and modulated according to information to be recorded, for example, “0” or “1”. In the process, the direction of the sublattice magnetization of the first magnetic thin film is aligned with the direction of the sublattice magnetization of the second magnetic thin film by the exchange coupling force of the first and second magnetic thin films, for example, “0”,
A recording bit (magnetic domain) of “1” is formed on the first magnetic thin film, and the compensation temperature of the second magnetic thin film composition is changed from room temperature to the second temperature T ₂ by a second external magnetic field.
At room temperature by choosing to be between
The sub-lattice magnetization of the second magnetic thin film is reversed only by the external magnetic field to obtain a state in which overwriting is possible. In this case, a special process (time) for erasure is performed.
It is possible to solve the problems that the transfer rate can be increased without the necessity of, or that the two-head method or the external magnetic field modulation method described above is used. In the present invention, these Japanese Patent Application Nos.
Utilizing the advantages of the thermomagnetic recording method disclosed in Japanese Patent Application No. 04961 and Japanese Patent Application No. 61-194962,
An object of the present invention is to provide a thermomagnetic recording medium and a thermomagnetic recording medium in which the above-mentioned second magnetic field is omitted or reduced, and therefore, an apparatus for performing the recording method can be further simplified. It is. A thermomagnetic recording medium according to the present invention comprises a rare earth-transition metal magnetic film, and has first, second and third magnetic thin films magnetically coupled to each other. The second and third magnetic thin films are coupled by exchange coupling force. The third magnetic thin film has a configuration in which the Curie temperature is set to be the highest as compared with the other magnetic thin films without reversing the magnetization even during the recording operation. According to the above-described thermomagnetic recording medium of the present invention, information is recorded only by giving a first and a second heating state (heating temperature) by modulating a laser beam in accordance with information to be recorded. And overwriting becomes possible. Further, according to the thermomagnetic recording medium of the present invention, binary recording can be performed with only one magnetic field applying means. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, the basic structure of a thermomagnetic recording medium according to the present invention is to form a first, second and third magnetic thin films 1 on a light-transmitting substrate 5. 2 and 3 are laminated. For example, as shown in FIG. 2 as a schematic cross-sectional view of an example, a light transmitting substrate 5 such as a glass plate or an acrylic plate is used.
The first, second, and third magnetic thin films 1, 2, and 3 are formed on one surface of the substrate via a transparent dielectric film 6 serving as a protective film or an interference film. Each of the first to third magnetic thin films is formed of a rare earth-transition metal perpendicular magnetization film. Then, a protective film 7 made of a dielectric film is formed on the magnetic layer formed by laminating the magnetic thin films 1 to 3. However, in this thermomagnetic recording medium 10, the dielectric film 6 and the protective film 7 can be omitted. This thermomagnetic recording medium 10
Are magnetically coupled to each other by the exchange coupling force. In the above configuration, each of the dielectric films 6,
The third magnetic thin films 1 to 3 and the protective film 7 are respectively deposited,
Alternatively, it can be formed by sputtering or the like. The magnetic thin films 1 to 3 may be made of various magnetic materials. For example, Nd, Sm,
One or two or more rare earth metals (RE) such as Gd, Tb, Dy, Ho, etc., have x = 10 to 40 at%, and C
transition metals such as r, Mn, Fe, Co, Ni, and Cu (T
One or two or more of M) is 1-x = 90 to 60
Atomic%, and may be constituted by an amorphous alloy RE _X ™ _1-X . In this case, a small amount of other elements may be added. In this RE-TM amorphous alloy magnetic material, except that RE is Nd or Sm, R
The magnetic moment of E and the magnetic moment of TM are coupled antiparallel, resulting in ferrimagnetism,
The net magnetization is the difference between the respective sub-lattice magnetizations of RE and TM (the sum of the respective sub-lattice magnetizations when considering the sign of the magnetization direction). When the rare earth metal (RE) is composed of either Nd or Sm or a mixture thereof,
The magnetic moment of RE and the magnetic moment of TM are combined in parallel, so-called ferromagnetic, and the net magnetization in this case is the sum of the RE and TM sublattice magnetizations. For such a thermomagnetic recording medium 10,
Under the application of an external magnetic field H _ex substantially perpendicular to the film surface, the first
Of the temperature T ₁ for holding the Curie temperature T _c1 Exceeded by a second transition metal magnetic thin film 2 sublattice magnetization directions of the predetermined orientation (below the orientation referred to the positive direction) of the magnetic thin film 1 in first heating state, likewise by, under the application of an external magnetic field H _ex, almost Curie temperature T _c1 or more second sublattice magnetization direction of the transition metal of the magnetic thin film 2, the external magnetic field H _ex A second heating state at a second temperature T ₂ which is reversed in a direction opposite to the above-described forward direction (this direction is hereinafter referred to as a reversing direction), and the first and second temperatures T _{1 are provided.}
During the respective cooling processes from the first and second heating states by T ₂ and T ₂ , the direction of the sub-lattice magnetization in the third magnetic thin film 3 can be changed without inverting the sub-lattice magnetization of the second magnetic thin film 2. In the same direction as the sublattice magnetization of the third magnetic thin film 3, that is, in the same state as the unrecorded state. The first and second heating states can be performed by modulating the intensity of the laser beam on the thermomagnetic recording medium 10 according to the information to be recorded. As described above, the sub-lattice magnetization of the transition metal TM in the first magnetic thin film 1 is obtained only by modulating the laser beam for obtaining the first and second heating states in accordance with the information to be recorded. The binary information of, for example, "0" and "1" is recorded by the positive direction part and the reverse direction part. At this time, as described above, the third
The sub-lattice magnetization of the second magnetic thin film 2 is aligned in the same direction as the sub-lattice magnetization of the third magnetic thin film 3 without reversing the direction of the sub-lattice magnetization in the magnetic thin film 3. In the recording state, both the second and third magnetic thin films 2
Since the directions of the sub-lattice magnetizations of the magnetic recording medium and the magnetic recording medium have the same state as the initial state of the unrecorded information on the magnetic recording medium, the first and second recordings corresponding to the recorded information are performed in the next recording. A state in which this recording is possible, that is, a state in which overwriting is possible is obtained only by giving a heating state. To read out, ie, reproduce, the recorded information from the thermomagnetic recording medium on which the information has been recorded in this manner, the first magnetic thin film 1 is irradiated with a linearly polarized laser beam, and the first magnetic thin film 1 is irradiated with a linearly polarized laser beam. By detecting, for example, the Kerr rotation angle by the interaction, binary reading, for example, “0” and “1” depending on whether the sublattice magnetization of the transition metal TM of the first magnetic thin film is the positive direction or the inverting direction is performed. As described above, information is recorded on the thermomagnetic recording medium 10 by, for example, “0” and “1” in the first magnetic thin film 1 depending on the positive direction portion and the reverse direction portion of the TM sublattice magnetization. The Curie temperature T _{C1 of} the first magnetic thin film 1 and the second magnetic thin film 2 in an exchange-coupled state with the first magnetic thin film 1 are obtained.
And the magnetization state at a temperature equal to or lower than T _C2 is the state A shown in FIG.
To D can be adopted. In FIG. 3, only the first and second magnetic thin films 1 and 2 schematically show the respective directions of TM spin and RE spin with solid arrows and broken arrows, respectively. It is assumed that the axes of easy magnetization of both magnetic thin films 1 and 2 are so-called perpendicular magnetization films in the direction perpendicular to the film surface, but it is sufficient that at least one of them is a perpendicular magnetization film. In FIG. 3, state A and state B are the first
The TM spins of the magnetic thin film 1 and the second magnetic thin film 2, ie, the magnetic moments of the TMs, and the RE spins, ie, the magnetic moments of the REs, are in the same direction. On the other hand, in the states C and D of FIG. 3, the magnetic moment of each TM and the magnetic moment of the RE of the first magnetic thin film 1 and the second magnetic thin film 2 are opposite to each other. In the vicinity of the interface, each direction of the magnetic moment of TM and the magnetic moment of RE is 1
Will be 80 ° changing regions or interface wall 9 is present, the interface wall energy (per unit area σ _w erg / cm ²⁾ is stored in this portion. A thermomagnetic recording apparatus for performing thermomagnetic recording, for example, as shown in FIG.
For example, a laser beam R for recording and reproduction is applied to the disk-shaped thermomagnetic recording medium 10 by the light transmitting substrate 5 shown in FIG.
For example, a magnet 21 and, if necessary, a magnet 22 are provided from the side of the protective film 7 or the substrate 5 to apply the magnetic fields _Hex and _Hsub to the medium 10. In FIG. 4, a magnet 21 and a magnet 22 are shown.
Are arranged apart from each other, but may be arranged adjacent to each other. When the magnetic field H _sub is not required as described later, the magnet 22 is omitted. The disk-shaped thermomagnetic recording medium 10 includes a rotating shaft 26 of a drive motor 25.
To be driven to rotate. Then, the power of the laser beam R is modulated in accordance with the information to be recorded, and the laser beam irradiation section of the thermomagnetic recording medium 10 is heated to the first and second temperatures T ₁ and T _2. ing. Next, the present invention will be described with reference to examples, but it goes without saying that the present invention is not limited to these examples. Embodiment 1 In this embodiment, only an external magnetic field _Hex is applied. The magnetic recording medium 10 used here includes first, second and third magnetic recording media.
And each of the magnetic thin films 1 to 3
FIG. 5 shows the relationship between the coercive force _{Hc and} the temperature characteristic.
First magnetic thin film 1 as the middle curve 101 to 103 recorded bit coercive free layer as shown in is a large coercive force at room temperature T _R, the Curie temperature T _C1 is low and the third magnetic thin film 3 The one having the highest Curie temperature T _C3 and a high coercive force near the Curie temperature T _{C2 of} the second magnetic thin film 2 is selected. That is, the first to third magnetic thin films 1 to 3
Each Curie temperature T _C1 through T _C3 of is selected to _{T C3> T C2> T C1} , the third magnetic thin film 3 is selected to the material magnetization reversal does not occur in the information recording process. As the second magnetic thin film 2 are shown in FIG. 5, it is constituted by a coercive force material having low at room temperature T _R, the third magnetic thin film 3 constant magnetic state is coercive of TM TM-rich or RE-rich is determined so that the direction of the TM sublattice magnetization when inverted by the external magnetic field _Hex is opposite to the direction of the sublattice magnetization. The first magnetic thin film 1 may be either RE-rich or TM-rich. Table 1 shows the composition, film thickness, and characteristics of an example of each of the magnetic thin films 1 to 3. [Table 1] In this case, the first and third magnetic thin films 1 and 3 are Fe-rich or TM-rich below their respective Curie temperatures, and the second magnetic thin film 2 is Tb-rich or RE-rich. The information recording process in this case will be described with reference to FIG. In this case as well, FIG.
In each of the magnetic thin films 1 to 3 in the middle state, the TM spin or the magnetic moment is schematically indicated by a solid arrow, and the RE spin or the magnetic moment is indicated by a broken arrow. In this case, the first and the second for the binary recording
The temperatures T ₁ and T ₂ of the first temperature T ₁ are close to the Curie temperature T _C1 of the first magnetic thin film 1, for example, T 1
₁ ≒ 130 ° C., and the second temperature T ₂ is close to the Curie temperature T _C2 of the second magnetic thin film 2, for example, T ₂ ≒ 200
° C. [0030] Now, in the initialization state at room temperature T _R, is in the state A in which the first and second magnetic thin films 1 and 2 is described in FIG. 3, TM spin of the third magnetic thin film at this time is the first And in the same direction as the TM spin of the second magnetic thin films 1 and 2. The required external magnetic field _Hex is, for example, the TM of the first and second magnetic thin films 1 and 2 in the state A.
It is given in the same direction as the sublattice magnetization. When the temperature T is increased to the first temperature T ₁ in this state, the magnetization of the first magnetic thin film 1 disappears or decreases as shown in the state N when the temperature T is near T _C1. In this state, the second and third magnetic thin films 2 as shown in FIG.
And 3 have a required large coercive force, so that the reversal of the TM and RE sublattice magnetizations caused by the external magnetic field _Hex is prevented from occurring, so that the temperature rise state is reduced. During the cooling process, the TM and RE sublattice magnetizations in the same direction as the initial state A are generated in the first magnetic thin film 1 by the exchange coupling force with the second magnetic thin film 2, and the state returns to the state A and returns to the information “0”. Is formed. On the other hand, when the temperature T is raised to the second temperature T _2, that is, near the Curie temperature T _{C2 of} the second magnetic thin film 2, the magnetization of the first magnetic thin film 1 becomes as shown in a state O of FIG. as well as the magnetization of the second magnetic thin film 2 is lost little or lost, because at this time has a third magnetic thin film 3 sufficiently large coercive force at this temperature, the outside also in the temperature T ₂ A predetermined magnetization direction is maintained without being affected by the magnetic field _Hex . [0033] However, for the second magnetic thin film 2 and the direction of the magnetization in the cooling step by the external magnetic field H _ex is oriented in an external magnetic field H _ex. That is, as shown in the state P, the TM sublattice magnetization has a direction opposite to that of the external magnetic field _Hex ,
Therefore, the TM sublattice magnetization of the second magnetic thin film 2 is opposite to the TM sublattice magnetization of the third magnetic thin film, and an interface domain wall 9 is generated between the two magnetic thin films 2 and 3. Further, when the temperature T approaches the Curie temperature T _C1 of the first magnetic thin film 1 in the cooling process, the magnetization appears in the first magnetic thin film 1. At this time, the temperature characteristics and the film thickness of the first magnetic thin film 1 By such selection, the TM sublattice magnetization is aligned with the direction of the TM sublattice magnetization of the second magnetic thin film 2 to obtain the state Q. When the temperature T is further decreased, the coercive force of the first magnetic thin film 1 increases, and this magnetization state is coerced. However, in the configuration of the medium 10, the second and third magnetic thin films 2
And 3, the first and second domain wall energies are selected to be smaller than the domain wall energy between the second and third magnetic thin films 2 and 3. The direction of the sub-lattice magnetization of the magnetic thin film 2 is reversed, and the state C shown in FIG. 3 is given to form a recording portion of information "1". Then, when the temperature is increased to the temperature T ₁ or T _{2 in} order to write the next information including the write portion of the information “1”, the portion of the state A is also changed to the state C. Both the TM and RE in the second magnetic thin film 2
Since the respective sub-lattice magnetizations are oriented in opposite directions, the transition to the state N occurs in any case. Therefore, the same information as described above, for example, writing “0” and “1” is written. That is, overwriting can be performed. In the example described above, the binary information based on the states A and C is performed.
6 are replaced with states A and C in FIG.
It is also possible to record value information. In this case, the external magnetic field _Hex is selected in the direction opposite to that of FIG. In each of the above-described examples, the case where each of the magnetic thin films 1 to 3 has ferrimagnetism has been described, but a ferromagnetic film may be used. As is apparent from the above description, according to the present invention, a high transfer rate can be realized because an erasing process (time) is not required. Since the system is not used, the structure can be simplified, and furthermore, since recording can be performed by heat modulation, for example, laser beam modulation without using external magnetic field modulation, high-speed recording can be achieved, and furthermore, it is simple. There are many advantages such as simplification of the apparatus, which can be achieved by being combined with one laser beam. In the present invention, the third magnetic thin film 3
Is provided so that overwriting can be performed together with binary information recording using only the external magnetic field _Hex regardless of other external magnetic fields.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a basic configuration diagram of a thermomagnetic recording medium of the present invention. FIG. 2 is a sectional view of an example of a thermomagnetic recording medium according to the present invention. FIG. 3 is an explanatory diagram of transition between magnetization states. FIG. 4 is a schematic configuration diagram of a recording apparatus. FIG. 5 is an explanatory diagram of a magnetization process of an example of the thermomagnetic recording medium according to the present invention. FIG. 6 is an explanatory diagram of a magnetization process of the thermomagnetic recording medium according to the present invention. [Description of Signs] 1 to 3 First to third magnetic thin films, 10 thermomagnetic recording medium, R laser beam, 21, 22 magnet, 25 drive motor

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Fuji Tanaka               6-7-35 Kita Shinagawa, Shinagawa-ku, Tokyo So               Knee Co., Ltd.

Claims (1)

(57) [Claims] A thermomagnetic recording medium comprising a rare earth-transition metal magnetic film, magnetically coupled to each other, having first, second and third magnetic thin films, wherein the second and third magnetic thin films are exchange-coupled; The third magnetic thin film has a Curie temperature higher than that of the other magnetic thin films, and has a first magnetic thin film formed by binary recording at first and second binary temperatures. A thermomagnetic recording medium wherein the sublattice magnetization reversal does not occur in the third magnetic thin film during the information recording process by reversing the sublattice magnetization of the second magnetic thin film.