JPH0823926B2 - Magnetic head - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic head for highly sensitively detecting a magnetic field in a spatially minute region, for example, a magnetic field generated from a magnetic recording medium.

<Prior Art> The field in which the detection of a magnetic field in a minute area is most needed is a magnetic recording technology. In the conventional magnetic recording technology, a magnetic field generated from a minute medium surface of about 10 μm ² per bit can be detected as a reproduction signal. Another feature of this magnetic field is that the magnetic field distribution in the direction perpendicular to the medium surface is extremely steep and sharply decreases as the distance (Z) from the medium surface increases. For this reason, in the conventional magnetic head, the most important point for improving the sensitivity is how to reduce the distance from the medium. For a hard disk,
The space between the magnetic head and the medium can be narrowed to about 0.2 μm. The current magnetic head requires a track width of at least 10 μm in order to secure a sufficient reproduction output. The linear density of bits that can be detected using such a magnetic head is 1000 bits / mm or more. That is, the bit shape is a quadrangle with the long side in the track width direction. Therefore, it is effective to reduce the track width in order to improve the areal recording density in magnetic recording.

Magnetic transfer heads have been studied as a technique for reducing the track width to the μm order (Nomura, Tokumaru; Journal of the Institute of Electronics and Communication Engineers, J68-C, No. 3, pp216-223, 1985). This is because the information recorded on a magnetic material is transferred as a striped domain pattern to a multi-domain magnetic film with a large magneto-optical effect, while the easy axis of magnetization is generally oriented perpendicular to the film surface such as a YIG film. However, the magnetic domain pattern is optically read by utilizing the Kerr effect or the Faraday effect. With this head, it is considered that the detectable track width of the bit can be ultimately reduced to about 1 μm because the size of the light beam is the limit in principle. However, there are also the following drawbacks.

(1) The length of the transferable bit is about the stripe domain width, and the minimum is about 5 μm at present. The width of the stripe domain is determined by the equilibrium of three factors of domain wall energy, magnetostatic energy, and Zeeman energy. Therefore, for a signal having a bit length of about the stripe domain width, the magnetic domains are aligned along the bit without increasing the total energy, that is, the transfer efficiency is high. On the other hand, if the bit length is shorter, the Zeeman energy is insufficient and transfer cannot be performed.

(2) Since the stripe domains are continuous, they are easily affected by the magnetic domain patterns of adjacent tracks. Such a magnetic domain state prevents movement of the transfer magnetic domain and also causes crosstalk when the track is narrowed.

On the other hand, as a magnetic head capable of detecting a magnetic field in a minute area, a micro magnetic head (Japanese Patent Application Nos. 58-87557 and 59).
-78357, etc.) FIG. 4 shows the structure of a micro magnetic head. In the figure, 1 is a head magnetic film pattern, 2 is a uniform external magnetic field for bias (Hb), 3 is a magnetic recording medium, and 4 is an optical path of a polarized beam.

The operating principle of the micro magnetic head is as follows,
The operation mechanism is the magnetization reversal due to the magnetization rotation.
As the head magnetic pole, a single domain thin film having in-plane uniaxial anisotropy is used, and the extent to which the magnetization in the head magnetic pole is tilted in the direction of the magnetic field when a signal magnetic field (H _S ) is applied is calculated by the Kerr effect or Faraday effect. This is a method of detection using the magneto-optical effect. In this case, the signal detection resolution is equal to the head magnetic pole thickness, so that the magnetic field in an extremely small area can be detected. In particular, the longitudinal direction of the head magnetic pole (that is, the direction parallel to the signal magnetic field)
Is set as the easy magnetization direction, and a high-frequency magnetic field having an amplitude equal to or larger than the anisotropic magnetic field (H _K ) is applied as a bias external magnetic field (Hb) in a direction perpendicular to the direction (that is, the track direction), The sensitivity can be improved by the following mechanism.

When the absolute value of the bias magnetic field | Hb | is greater than or equal to the anisotropic magnetic field H _K , the magnetization in the head magnetic pole is oriented in the direction of the bias magnetic field, but when | Hb | decreases to zero, Magnetization is aligned in the easy magnetization direction (two directions, upward and downward, are equivalent). At this time, the factor that determines whether the magnetization in the head magnetic pole is upward or downward is the signal magnetic field.
Since there is only interaction energy (Zeeman energy) between H _S and the magnetization in the head magnetic pole, it is possible in principle to detect an infinitely small signal magnetic field.

However, in reality, there is a problem that the sensitivity of the micro magnetic head is lowered due to the following reasons.

It is quite difficult to form a material having soft magnetic properties (for example, permalloy, an amorphous alloy such as Fe-B or C 2 _{O 3} -Zr) generally used for a head magnetic pole into a single domain thin film. That is, since the spontaneous magnetization (M _S ) of these materials is large, the magnetostatic energy due to the magnetic charge generated at the head magnetic pole pattern end is large, and in order to realize the single domain state, the size of the pattern is on the order of μm or less. And need to. At the same time, in order to reduce the magnetostatic energy, the magnetic moment is inclined so that the magnetic moment becomes parallel to the pattern end (this is called curling), and the surface magnetic charge is distributed so as to decrease. Therefore, in principle, if a single domain thin film pattern with in-plane magnetization is used for the head magnetic pole, sensitivity should be improved by a method such as applying a bias magnetic field, but in reality, the pattern size is extremely small, so the polarized light is focused. Then, even if the direction of magnetization is detected by the Kerr effect or Faraday effect, the pattern size is smaller than the light spot size, and the size of the effective magnetization of the part radiating light is affected by the curling effect described above. Since it becomes lower than the saturation value, there is a problem that the reproduction output value decreases, that is, the sensitivity decreases.

<Problems to be Solved by the Invention> In view of the above-mentioned conventional technique, the present invention is affected by (1) the limit of transferable bit length as in a magnetic transfer head using stripe domains and the magnetic domain pattern of an adjacent track. (2) It is an object of the present invention to provide a magnetic head which does not have the drawback of being easy, and (2) does not have problems such as sensitivity reduction due to minute patterns and curling as in a micro magnetic head.

<Means for Solving Problems> A magnetic head according to the present invention that achieves the above-mentioned object is
The magnetic pole is composed of a magnetic film whose direction perpendicular to the film surface is the easy axis and whose anisotropic magnetic field (H _K ) is larger than the self-demagnetizing field (4πM _S ).

<Operation> With the above configuration, the magnetic pole of the magnetic head is a single domain film with perpendicular magnetization, and is not affected by the striped domain as in the conventional magnetic transfer head. Further, it is not necessary to make the pattern small, and the signal magnetic field triggers the magnetization reversal due to the nucleation, resulting in an extremely large reproduction output as compared with the conventional magnetic transfer head or the micro magnetic head. These will be described in detail below.

Anisotropic magnetic field (H _K ) is self-demagnetizing field (4πM _S , M
_{If S} is more than spontaneous magnetization, the magnetic moment is perpendicular to the film surface, so a striped domain is formed in the absence of an external magnetic field, and a certain constant value is perpendicular to the film surface. Bubble magnetic domains are formed when a magnetic field is applied. When the magnetic field perpendicular to this film surface is strengthened, the diameter of the magnetic bubble decreases and finally disappears. Magnetic field the magnetic bubble disappears is called the collapse field (H _C), collapse field (H _C) is generally smaller order of magnitude more than the anisotropy field (H _K). As a material for such a bubble domain device, a ferrimagnetic oxide film such as YIG is used. In such a material, the spontaneous magnetization (M _S ) is about 100 emu / cc or less, and permalloy or F
Compared with eB, Co-Zr amorphous alloys, etc., the value is smaller by about one digit. For this reason, the magnetostatic energy becomes small, and it is several hundred μm
It is known that a single domain film can be easily formed by adopting the pattern of (for example, literature H. Uchishiba, H. Tomina.
ga, T.Obotaka and T.Namikata; “Growth and Propertie
s of Stable Self-biasing Double Layer Epitaxial Ga
rnet Films "IEEE Trans.Magn., MAG-10,1974, PP480-48
3).

The fact that the head magnetic pole has a single magnetic domain film pattern is largely different from the conventional magnetic transfer head having multiple magnetic domains, and the influence of the striped magnetic domain (stripe domain) is eliminated.
Further, since the single domain film pattern is considerably larger than that of the micro magnetic head, the adverse effect of the small pattern in the micro magnetic head is eliminated.

In the magnetization reversal of the single domain film pattern as described above, when the magnetic field antiparallel to the magnetic moment increases, a reversal magnetic domain occurs above a certain magnetic field (this is called nucleation), and this reversal occurs. It occurs by the mechanism that the magnetic domain spreads over the entire pattern. When the magnetic field in which such magnetization reversal occurs, that is, the nucleation magnetic field (Hn) is smaller than the collapse magnetic field (H _C ), stripe domains or bubble domains are formed in the film at the time when the reversal domain is sprung, Only when the antiparallel magnetic field increases to the collapse magnetic field (H _C ), the bubble domain disappears and the entire pattern saturates in a certain direction. On the other hand, when the nucleation magnetic field (Hn) is higher than the collapse magnetic field (H _C ), the reversal domain is more stable than the conventional domain at the time of nucleation, so no bubble domain or stripe domain is formed. , Magnetization reversal occurs instantaneously.

Since nucleation generally occurs at a location where magnetic field concentration occurs, such as at the edge of a single domain film pattern, the angular portion of the pattern is the most sensitive portion to an external magnetic field. That is, when the perpendicular magnetic film as described above is used as the head magnetic pole, one of the corners of the pattern is set close to the recording medium to set the signal magnetic field (H _S ) at this corner.
When is added, this acts as a trigger and the behavior of the creation is most strongly affected. That is, when the bias external magnetic field (Hb) and the signal magnetic field (H _S ) are in the same direction, magnetization reversal occurs when the condition | Hb + H _S | ≧ Hn is satisfied. By detecting (Hb), the polarity and magnitude of the signal magnetic field (H _S ) can be detected. Almost two spontaneous magnetization magnetization variation perpendicular magnetization single domain film pattern associated with the magnetization reversal from -M _S to + M _S
In addition, since the size of the pattern itself can be set to several tens of μm or more, the conventional micro magnetic head cannot detect the change amount of twice the spontaneous magnetization because the pattern size is small and the magnetic moment is curling. Compared with the above, an extremely large reproduction output can be obtained.

Example 1 FIG. 1 shows an example of the present invention. In the figure, 5 is the magnetic film pattern of the head magnetic pole, and the perpendicular magnetic film is patterned into a minute shape to change the nucleation magnetic field (Hn) to the vanishing magnetic field of the magnetic bubble, that is, the collapse magnetic field (H _C ).
A larger film is used. In other words, a magnetic domain wall exists in the film of the head magnetic film pattern 5 at the moment of magnetization reversal, but in other cases, the magnetization is saturated in either the upper or lower direction and the entire pattern is in a single domain state. .

In FIG. 1, 2 is a uniform external magnetic field for bias, 3 is a magnetic recording medium, and 4 is an optical path of a polarized beam for measuring a magneto-optical effect.

The absolute value | Hb | of the uniform external magnetic field 2 is set to be larger than the collapse magnetic field (H _C ) and smaller than the nucleation magnetic field (Hn), and its polarity is set so as to always face the magnetization direction of the head magnetic film pattern 5. Is designed to be changed. Specifically, since the magnetization direction in the head magnetic film pattern 5 can be detected by detecting the rotation direction of the polarization plane of the polarized beam as the difference in light intensity after passing through the polarizer, a switching circuit (not shown) is used. By generating the uniform external magnetic field 2 in conjunction with each other, it is possible to set such that the uniform external magnetic field 2 facing the magnetization is applied every time the magnetization in the head magnetic film pattern 5 is reversed.

In this case, | H _C | <| Hb | <| Hn |, so if a uniform external magnetic field (Hb) is simply applied,
The magnetization of pattern 5 does not change at all.

However, when a magnetic field generated from the recorded medium 3 or the like, that is, a signal magnetic field (H _S ) is applied to the head tip portion and | Hb + H _S | ≧ | Hn |, the head tip portion 6 generates a reversed magnetic domain. (Nucleation), the pattern 5 is completely saturated in the direction of the uniform external magnetic field 2 by expanding to the entire pattern. That is, the signal magnetic field (H _S ) triggers the magnetization reversal. Of course, at this time, | Hb |> | H _C |, so no bubble domain or stripe domain remains in pattern 5.

Since the magnetization reversal in the pattern 5 can be detected by the Faraday effect or the like as described above, by reversing the polarity of the uniform external magnetic field 2 at each magnetization reversal, the polarity change of the signal magnetic field (H _S ) can be detected. It can be detected as a change in polarity of Hb).
Further, by changing the value Hb of the uniform external magnetic field 2, the magnetization reversal occurs only when the condition | Hb + H _S | ≧ | Hn | is satisfied, so the absolute value | H _S | of the signal magnetic field can also be known.

Referring to FIGS. 2 and 3, the head magnetic film pattern 5
A specific example of will be described. As pattern 5, L on the GGG substrate
A 2 μm thick YIG film formed by the PE method was processed by photolithography into the shape shown in FIGS. 2 and 3. The diameter of the circular portion in FIG. 2 is 30 μm, and the portion designated by the reference numeral 6 corresponding to the head tip portion is particularly wedge-shaped etched as shown in FIG. The width of the head tip portion 6 is 1 μm or less. YIG is attached with Sm, Ca, Ge, the saturation magnetization is 155emu / cc, the vertical uniaxial anisotropy constant is 9000erg / cc, and the vanishing magnetic field (H _C ) of the bubble domain before patterning is It is 118 Oe. In the patterned film 5, when only a magnetic field (Hb) in the vertical direction is applied to the film, bubble domains and stripe domains are not formed, and the entire pattern becomes a single magnetic domain. The magnetic field (Hn) at which the magnetization reversal of this pattern 5 occurs is 160 Oe. When a magnetic field of 157 Oe is applied as a uniform external magnetic field (Hb), a signal magnetic field of H _S ≧ 3 Oe can be detected. In the pattern 5, the region to which the signal magnetic field (H _S ) should be applied has only to be large enough to generate the buds of the reversal domain, and after the reversal domain is generated, the reversal domain is expanded by the domain wall movement. Therefore, it is sufficient to invert in a very small area. In the case of this embodiment, a metal tape (coercive force: 1000 Oe, saturation magnetization: 210 emu / cc, film thickness: 4.2 μm) was used as a recording medium, and a signal of 1000 bits / mm was recorded in advance by a ring head. It was completely reproducible. Further, in FIGS. 2 and 3, the width of the head tip portion is set to 1 μm or less, so that it can be said that the reproducing ability is 10 ⁶ bits / mm ² or more.

Meanwhile, the bias for the external magnetic field 2 (Hb), not only using the direct-current magnetic field linked to the reproduction output, a high frequency of at least twice the frequency of the reproduction output frequency, and the amplitude | Hb | is | H _C | The same effect can be expected by setting the value as close to | Hn | as possible within the range of <| Hb | <| Hn |. That is, | H _C | <| Hb | <| H
n | in the case of the magnetization direction in the pattern 5 unless applied signal magnetic field (H _S) is constant, and the signal magnetic field (H _S) is also the signal magnetic field applied (H _S) and pattern 5 in the If the magnetization direction is the same, the magnetization direction remains unchanged, but if the signal magnetic field (H _S ) is anti-parallel to the magnetization direction in the pattern 5, an inverted magnetic domain is generated from the portion to which the signal magnetic field (H _S ) is applied. It also enlarges and causes magnetization reversal. That is, the high-frequency external magnetic field (Hb) during the half cycle change of the signal magnetic field (H _S ).
Changes at least one cycle, so the signal magnetic field (H _S )
The magnetization direction of the pattern 5 will change in accordance with the polarity of. The absolute value | H _S | of the signal magnetic field can be measured by changing the amplitude | Hb | of the high-frequency external magnetic field and measuring the value when the magnetization reversal occurs.

<Embodiment 2> In the magnetic head according to the present invention, as is apparent from the operation mechanism described in <Embodiment 1>, the magnetization in the head magnetic film pattern 5 is always aligned upward or downward with respect to the film surface. Therefore, it is also important that the reversal domain is always generated from the same place with the same nucleation magnetic field (Hn). If a disturbance external magnetic field other than the signal magnetic field (H _S ) and the external magnetic field (Hb) as a bias is strongly applied to the other region from the tip 6 of the pattern 5, and in this case as well, The entire pattern causes magnetization reversal in the direction of the bias magnetic field (Hb), which means that the head malfunctioned.

In order to avoid this problem, the generation of the reversal domain is made to occur only in a certain part of the pattern 5, that is, the reversal domain is most likely to be generated by intentionally giving the distribution of the nucleation magnetic field (Hn). Is used to detect the signal magnetic field (H _S ).

As one of the methods, in <Example 1>, by thinning the film thickness of the signal magnetic field detecting portion into a wedge shape 7 as shown by reference numeral 6 in FIGS. As a result of the increase in the magnetic field generated from the surface magnetization of 7, i.e., the demagnetizing field, the nucleation magnetic field (Hn) of the detection tip portion 7 is made lower than the other portions of the pattern 5.

As a method of setting the nucleation magnetic field (Hn) of a certain part of the pattern 5 lower than that of the other part, several methods other than the method of <Example 1> can be considered. One of them is a method of raising the temperature of a portion where the nucleation magnetic field (Hn) is desired to be lowered to lower the magnetic anisotropy energy of the region and facilitating the magnetization reversal. As a specific example of this method, an experiment was conducted in which the laser beam was concentrated on the tip portion 6 of the pattern 5 used in <Example 1> to raise the temperature. By adjusting the laser power, Hn could be set arbitrarily from 160 Oe to H _C (118 Oe). The above experimental results show that heating causes the Hn of the tip portion 6 to decrease and the difference from the Hn of the other portions of the pattern 5 to increase. That is, by partial heating,
It is possible to reduce the probability of malfunction due to the ununiformity of the generation location of the reversed magnetic domain as described above.

In this <Example 2>, laser beam irradiation was used as the heating method. However, the same effect can be obtained by heating with any other method such as a heater as long as the method can heat a minute region. On the contrary, the same effect can be obtained by a method in which the entire head magnetic film pattern is cooled and only the magnetic field detection unit is not cooled.

Here, a method of detecting the magnetization direction of the head magnetic film pattern 5 will be described. The size of the pattern 5 is usually several times as large as the stripe domain width or more, and since the entire pattern is saturated, the direction of magnetization can be detected by using the amount of change in the saturated magnetization of the entire pattern. Ability is large. Therefore, not only the magneto-optical effect is used, but all methods for detecting general magnetic bubbles can be used. For example, the magnetization direction of the pattern 5 can be detected by using the magnetoresistive effect or the Hall effect.

To further explain, the material satisfying 4πMs ≦ Hk is obtained by YIG, and if the materials mentioned in the examples are (YSmCa) ₃ (FeGe) ₆ O
It is a crystal of ₁₂ , and YIG produced by the LPE method on a GGG substrate generally has 4πMs ≦ Hk.

The patterning is to divide the YIG film or the like into a size of several tens of μm by a method such as micro-wrapping. The YIG film or the like isolated by the above method is called a pattern, and the entire surface of the pattern is one isolated. The entire surface of the YIG film or the like is called the entire pattern.

Further, regarding the magnetization reversal, the magnetization reversal of a general YIG film (having a size of several mm or more) proceeds by expanding a magnetic domain having a reverse magnetization according to an external magnetic field. The magnetic domain having the opposite magnetization to the external magnetic field shrinks as the external magnetic field increases, and the external magnetic field is collapsed (Hc).
When it reaches, the magnetic field disappears and becomes only a magnetic domain having a magnetization in the same direction as the external magnetic field (called a single magnetic domain). However, if the YIG film is patterned and the size of the continuous YIG film is divided into several tens of μm or less, a single magnetic domain state is obtained even when no external magnetic field is applied or when an external magnetic field of Hc or more is applied in the opposite direction to the magnetization. To be This phenomenon is described in the literature and the like.

In the magnetization reversal of the YIG film in this single domain state, when an external magnetic field in the direction opposite to the magnetization is applied, a bud of the switching magnetic domain (a region magnetized in the same direction as the external magnetic field) occurs, and this switching magnetic domain is a pattern. Proceeds with the mechanism of expanding the entire surface. The magnetic field generated by the buds of this inversion domain is the nucleation magnetic field (H
It is also known in the literature that there is a condition of Hn> Hc. 1 if the external magnetic field is above Hc
Since the energy is lower in the single domain structure in which the magnetizations are aligned in the direction of the external magnetic field than in the plurality of magnetic domains in each pattern, the generated inverted magnetic domain spreads over the entire surface of the pattern. While the generated inversion magnetic domain is expanding, there are two magnetic domains in the pattern, but they are energetically unstable and are allowed only at the moment of changing from the single magnetic domain to the single magnetic domain.

Therefore, in the pattern of a certain single domain, Hn>
In the state where a uniform external magnetic field (Hb) is applied in the range of Hc, the inversion domain does not occur and a single domain is obtained. In this state, when an external magnetic field is applied to a part of the pattern in the same direction as Hb to form a part of Hn or more, a reversal magnetic domain is generated and the above-mentioned magnetization reversal proceeds. The closer the value of Hb is set to Hn, the smaller the magnetic field (the magnetic field applied to a part of the pattern) of the inversion domain. That is, the magnetic field detection sensitivity increases.

As can be seen from the above, a magnetic body having a structure in which positive and negative magnetic charges are present on both surfaces of a thin film such as a YIG film has a multi-domain structure in order to reduce magnetostatic energy. Since the external magnetic field required to change from the single domain structure to the multiple domain structure is Hn, Hn decreases as the magnetostatic energy increases. Further, the magnetostatic energy increases as the interval between magnetic charges becomes narrower, that is, as the YIG film becomes thinner.
Therefore, if the film thickness of a part of the pattern is thinned to intentionally create a low Hn part, this part forms a bud of a reversed domain with the lowest external magnetic field. Therefore, the change in the external magnetic field can be detected with the highest sensitivity, which is suitable for the detection when the magnetic field emitted from the magnetic recording medium such as a magnetic head exists only in a limited region near the surface. In other words, reducing the thickness of part of the pattern or heating with a laser is
The purpose is to form a region where the magnetic field detection sensitivity is increased by decreasing Hn.

By the way, in addition to the magneto-optical effect, the above phenomenon can be detected as long as it is a method capable of detecting the magnetization reversal behavior of YIG or the like, and the Hall element or the magnetoresistive effect element is attached to the YIG film surface as described above, or Place a small coil and YI
It is possible to detect the change in magnetic field due to the reversal of G magnetization. That is, the magneto-optical effect is only one of the magnetization detecting means.

<Effects of the Invention> The magnetic head according to the present invention differs from a magnetic transfer head or a micro-magnetic head that uses a magnetic thin film having a stripe domain as a transfer film, which has been conventionally used, and generates a reversal domain (nucleation) and its propagation. Since the magnetization reversal mechanism is used as a trigger and the signal magnetic field is used as a trigger for generating a reversal magnetic domain, high sensitivity can be achieved. Moreover, when the method of detecting the change in magnetization is used as the output detection mechanism, the conventional magnetic transfer head detects the change in magnetization in the area in which the stripe domain has an area substantially equal to that of the recording bit. Then, the change amount of the saturation magnetization of the entire head magnetic film pattern, which is usually several times as large as the stripe domain width or more, is detected, which is easy to detect and the reproduction output amount is greatly increased. The increase in reproduction output is remarkable even when compared with the micro magnetic head.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a magnetic head according to the present invention, and FIG. 2 is a plan view showing the pattern of the magnetic poles of the head.
FIG. 3 is a side view of the same. FIG. 4 is a block diagram of a conventional micro magnetic head. In the drawing, 2 is an external magnetic field (Hb), 3 is a magnetic recording medium, 4 is a polarized beam optical path, 5 is a head polar film pattern, 6 is a detection tip portion, and 7 is a wedge shape.

Claims (5)

[Claims] 1. A magnetic head in which a head magnetic pole is composed of a magnetic film whose direction perpendicular to the film surface is an easy axis of magnetization and whose anisotropic magnetic field (H _K ) is larger than a self-demagnetizing field (4πM _S ). 2. The magnetic film according to claim 1, wherein the magnetic film is patterned, and an inversion magnetic domain is generated in a magnetization reversal mechanism in a perpendicular direction on the film surface of the magnetic film, and the reversal magnetic domain spreads over the entire surface of the pattern. A magnetic head characterized in that the nucleation magnetic field (Hn) generated by the inversion domain is larger than the collapse magnetic field (H _C ) required for disappearance of the bubble domain existing in the magnetic film which is not patterned. 3. The uniform external magnetic field (Hb) applied perpendicularly to the magnetic film according to claim 1 or 2, wherein the uniform external magnetic field (Hb) is more than the collapse magnetic field (H _C ) and less than the nucleation magnetic field (Hn). A magnetic head characterized in that 4. The film according to claim 1, 2 or 3, wherein one specific corner of the magnetic film has a thinner film thickness than the other corners. Nucleation magnetic field (Hn) more than other parts in the head magnetic pole
And a magnetic head in which a reversed magnetic domain is generated from the specific corner portion. 5. The method according to claim 1, 2 or 3, wherein one specific corner of the corners of the magnetic film is kept at a temperature higher than that of the entire magnetic film. The magnetic anisotropy energy of the specific corner is set low due to the temperature difference, the nucleation magnetic field (Hn) of the specific corner is lower than other parts in the head magnetic pole, and the reversal domain is generated from the specific corner. head.