JPH03273540A - Magnetic recording medium and magnetic recording device and spin glass magnetic material - Google Patents

Abstract

PURPOSE:To allow recording and reproducing without contact and easy overwriting and many valued recording by using a spin glass magnetic material as a recording layer. CONSTITUTION:The spin glass magnetic material layer is provided as the magnetic recording layer 3 on a base body 2. The spin glass magnetic material refers to a material which is in a paramagnetic state at a high temp., but has the higher interaction between spins and generates a certain kind of magnetic order at a low temp. The magnetic recording device has a heating means 5 for heating the spin glass magnetic material to the spin freezing temp. or above and a magnetic field generating means 6 which can vary the magnetic field to be impressed to the spin glass magnetic material by at least >=2 values at the time of cooling. The magnetic recording medium and magnetic recording device which can be make recording and reproducing without contact and allow the easy overwriting the many valued recording as well are obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Objective of the Invention (Field of Industrial Application) The present invention relates to a magnetic recording medium, a magnetic recording device, and a novel spin glass magnetic material.

(Prior Art) Various magnetic recording technologies have been developed and put into practical use. For example, a method uses a recording medium such as a magnetic tape or a magnetic disk, and performs recording/reproduction with a magnetic head, and a method uses a magneto-optical disk, which uses a laser beam as a heating source, records by an applied magnetic field, and reads by the magneto-optic effect. Examples include bubble memory, which performs recording and reproduction depending on the method used and the presence or absence of bubble magnetic domains.

Each technology has its advantages and disadvantages, and research and development is progressing. For example, in technologies using magnetic disks, it is desired to further improve the recording density, and in magneto-optical disks, it is desired to improve the C/N and establish override technology.

(Problems to be Solved and Solved by the Invention) The present invention proposes a novel magnetic recording method that has never existed before, thereby enabling magnetic recording that enables non-contact recording and reproduction, easy override, and multilevel recording. It is an object of the present invention to provide a novel spin glass magnetic material suitable for use as a medium and a magnetic recording device, and particularly as a magnetic recording medium.

The present invention was made by focusing on the unique magnetic properties of spin glass magnetic materials, that is, the difference in magnetization between cooling in a magnetic field from a temperature above the spin freezing temperature and cooling in a non-magnetic field. The magnetic recording medium of the present invention is a magnetic recording medium characterized by comprising a spin glass magnetic layer as a magnetic recording layer on a substrate. Here, a spin glass magnetic material is one that is in a paramagnetic state at high temperatures, but at low temperatures the interaction between spins increases and a certain type of magnetic order occurs. However, the magnetic order in this case is not a spin structure like so-called ferromagnetism or antiferromagnetism, but an irregular spin arrangement, and the AC magnetic susceptibility exhibits a cusp shape at the transition point (spin freezing temperature). There is. Such spin glass magnetic materials are often found in alloy systems containing dilute magnetic elements, amorphous alloy systems, and compound magnetic systems containing competing positive and negative exchange interactions, but are not limited to these.
As mentioned above, a magnetic material exhibiting a phenomenon in which the alternating current magnetic susceptibility has a cusp is called a spin glass in a broad sense. Such a magnetic recording medium can be used in the following magnetic recording devices.

The magnetic recording device of the present invention uses the above-mentioned magnetic recording medium, and includes a heating means for heating the spin glass magnetic body to a temperature higher than the spin freezing temperature, and a magnetic field applied to the spin glass magnetic body when cooling the spin glass magnetic body, which changes at least two values or more. The present invention is characterized in that it is equipped with a magnetic field generating means that can generate a magnetic field.

The magnetization value of spin glass magnetic materials differs not only depending on the presence or absence of a magnetic field during cooling from a temperature region above the spin freezing temperature, but also the magnitude of the magnetic field. Therefore, if we assume the recording of "0" and "1', we can make the presence or absence of a magnetic field correspond to each other, and if we change the applied magnetic field in multiple steps, we can change the magnetization value according to each applied magnetic field to the spin. Glass magnetic material can be used to record multiple values.

The case of binary recording of "0" and "1" will be explained using the N1 diagram. FIG. 1 shows the temperature characteristics of magnetization of a spin glass magnetic material. In the figure, ■ indicates the case of cooling in a non-magnetic field, and ■ indicates the case of cooling in a magnetic field.

Both lines behave the same at temperatures above Tr (critical point; spin freezing temperature), but behave differently at temperatures below T. The rear region (TR) is set to T or less, and the initial state (“0”) of the magnetization of the magnetic material is set to MA. When a magnetic material is heated to a temperature range of T2 or higher (for example, C) and cooled while applying a magnetic field, the magnetization changes to MB. This state is defined as "1". This means that "1" has been recorded by cooling in a magnetic field. Since this recording head can be realized even in a sufficiently small area, a high recording density can be achieved.

In addition, by heating the magnetic material to a temperature range of 75 or higher and cooling it in a non-magnetic field, M! Since the 1 state can be returned to the MA state, an erasing operation can be performed by such heat treatment.

An outline of an apparatus for realizing such a magnetic recording method will be explained with reference to FIG.

As a recording medium (1), a recording layer (3) made of spin glass magnetic material is formed on a transparent substrate (2), and a reflective film (4) is formed on the transparent substrate (2).
) is prepared. Each layer can be formed by various thin film forming methods such as sputtering.

For example, a laser is used as the heating means (5) for the recording layer (3). With this heating means (5), the recording layer (
3) Arrange so that it can be heated. Further, an electromagnet, for example, is prepared as a magnetic field generating means (6) for applying a magnetic field to the recording layer (3), and the recording layer (
3) Arrange it so that a magnetic field can be applied to it.

During recording, the region of the recording layer <3> heated to Tt or higher by the heating means (5) is cooled while applying a magnetic field by turning on the electromagnet of the magnetic field generating means (6>. Magnetization of this region The state is MB, which is a high magnetization state.

On the other hand, during erasing, the recording layer region heated to a temperature higher than Tr by the heating means (5) is cooled without applying a magnetic field by turning off the electromagnet of the magnetic field generating means (6). The magnetization state of this region is MA, which is a low magnetization state. In this way, recording and erasing can be easily performed simply by switching ON and OFF of the magnetic field generating means. In any case, record
Since there is no difference between erasing and raising the temperature to T1 or higher, for example, it is sufficient to continuously irradiate the recording layer with a laser beam and turn on the electromagnet only when recording 1''.

In this way, regardless of the magnetization state of the recording layer 3), recording can be performed depending on the presence or absence of an applied magnetic field after heating to T1 or higher, so it can be seen that overriding is easily possible.

In the above explanation, the initial state is MA, but M.

It goes without saying that the correspondence between "0 and 1" may also be reversed. Further, the recording layer does not need to be a single layer, and may be multilayered.

In the case of conventional magneto-optical recording, override using a magnetic field modulation method has also been developed, but in the case of magneto-optical recording, since the direction of perpendicular magnetization is used for identification, the magnetic field required for magnetic field modulation must exceed the coercive force of the recording layer. Switching such a large magnetic field in the high frequency range has been difficult since it requires a relatively large magnetic field. In the case of the present invention, recording is identified by the difference in the magnitude of magnetization, so the magnetization state of the recording layer can be changed significantly with a small magnetic field less than the coercive force, so even though it is called magnetic field modulation, it is fully compatible with high frequencies. can.

The reading method is not particularly limited as long as the difference in the magnetization value can be read out, but since changes in the magnetization value cause magneto-optical effects, such as differences in Faraday rotation angle and Kerr rotation angle, it is possible to read out the difference in the magnetization value. For example, the information can be read out based on the intensity of reflected laser light. It goes without saying that the magnitude of magnetization may also be directly read out using a magnetic head or the like.

In this manner, the magnetic recording according to the present invention allows recording, erasing, and reading to be performed without contact.

By the way, the magnetization of a spin glass magnetic material has a property of relaxing. That is, the magnetization MB during cooling in a magnetic field in FIG.
The state will approach MA as time passes. Utilizing this property, it can be used as a recording medium in which records disappear after a certain period of time; however, it is generally desired that records be maintained accurately for a certain period of time or longer. Although it is possible to extend this relaxation time by improving the spin glass magnetic material, this problem can also be solved by forming a bias layer in the recording medium that applies a bias magnetic field to the recording layer.

FIG. 3 shows an example of a magnetic recording medium having such a configuration.

It is basically the same as the medium shown in Figure 2, and the recording layer (
A bias layer (7>) is formed in contact with the recording layer (3).The bias layer (7) only needs to be located at a position where it can apply a magnetic field to the recording layer (3), as shown in Figure 3. There is no need for the bias layer (4) to be between the reflective film (4) and the recording layer (3).Also, since it is necessary to generate a magnetic field when the recording layer (3) is cooled from heating above the spin freezing temperature, the bias layer ( 7)
It is preferable that the Curie temperature of is equal to or higher than the spin freezing temperature.

Recording and erasing when using such a recording medium will be explained. It is assumed that the magnetization state of the recording layer in the initial state is MA, and the bias layer (7) is demagnetized (Fig. 4 (a)
)). Similarly to the above, during recording, the magnetization state of the recording layer becomes MB by cooling in a magnetic field after heating to T1 or more, and at this time, the bias layer (7) is also magnetized at the same time (
Figure 4 (b)).

Even after recording, a bias magnetic field is constantly applied to the recording layer (3) by the bias layer (7), so there is no fear of magnetization relaxation. Therefore, it becomes possible to maintain records for a long period of time.

Also, during erasing, the Curie temperature TC (
After heating to a temperature above TC>Tt), by cooling without a magnetic field, the magnetization state of the recording layer becomes MA, the bias layer is demagnetized, and the state returns to the state shown in FIG. 4(a).

Furthermore, by using the magnetic recording medium according to the present invention, multilevel recording can also be realized.

That is, as shown in FIG. 4, the property of the magnetization of the spin glass magnetic material changes depending on the magnitude of the applied magnetic field during cooling. For example, if the magnitude of the applied magnetic field is HO<
Let Hl < H2 × H*, and the corresponding magnetization is MA
, Ma, Mc, Mo, the value of magnetization is also M A
< M B < M (< M D holds true (Figure 5). Therefore, by changing the applied magnetic field in this way when performing magnetic recording using the method shown in Figure 2, it is possible to The magneto-optical effect can be similarly used for readout.Generally, the magneto-optical effect changes depending on the magnitude of magnetization, so reading can be done by converting the magnetization intensity into, for example, light intensity. Multi-level recording is also possible by multi-layering spin glass magnetic layers having different spin freezing temperatures.

Even in the case of multilevel recording, magnetization relaxation of the recording layer (3) may be a problem, but it can be solved by providing a bias layer (7). However, in this case, it is preferable to select a material that can generate a bias magnetic field corresponding to each recorded magnetization value, that is, a material that has residual magnetization of a magnitude corresponding to the magnitude of the applied magnetic field. If a too strong magnetic field is applied as a bias magnetic field, there is a risk that the recording layer (3) will be brought to a larger magnetization state than the magnetization relaxation is prevented.

The material constituting such a bias layer is required to have a large squareness ratio of the magnetization curve and appropriate coercive force and Curie temperature. Since the squareness ratio determines the magnitude of residual magnetization, it is better to make it as large as possible. In addition, if the coercive force is too large, the modulation magnetic field required for writing will become large, and if it is too small, it will no longer function as a bias layer.
A value on the order of koe is preferable. In addition, the Curie temperature is 1oo~200℃ so that it can be easily demagnetized during heating for erasing.
degree is preferred.

The material constituting such a bias layer is an amorphous rare earth-transition metal alloy.

Multilayer films such as Pt/Co, Pd/Co, rare earth garnet, C.

Ferrite, oxide thin film such as Ba ferrite, C.

Perpendicular magnetization film such as Cr alloy, γ-Fe2O3゜Fe3O
For example, an oxide thin film such as No. 4, an in-plane magnetized film such as a rare earth transition metal alloy film, etc. can be used. In addition, magnetic materials that exhibit different residual magnetization depending on the applied magnetic field include Pt/Co and Pd/
In addition to multilayer films such as Co, S+g(Co, Cu, M)z
(4,5≦2≦8.M-re, Mn, Cr+V, Nb,
Ta.

Examples include a magnetic film made of at least one of Tj, Zr, Hf, etc. This bias layer can also be formed by various thin film forming methods such as sputtering.

Now, regarding the spin glass magnetic material used in the present invention, although its magnetic behavior itself has been known for a long time, the spin freezing temperature is at most several tens of degrees below room temperature, and the search for practical applications is difficult. It had not been done. The present inventors have newly discovered that oxide thin films represented by ferrite composition thin films are spin glass magnetic materials, and furthermore, their spin freezing temperature is above room temperature, making it difficult to apply spin glass behavior to practical applications. We have discovered that this is possible and have created the present invention.

The spin glass magnetic material of the present invention is a thin film with a ferrite composition,
It is characterized by the fact that the spins of magnetic ions are frozen without long-range order below a certain temperature.

When a ferrite crystal with oxide ferrimagnetism is topologically disordered, for example, some originally square lattices form triangular lattices, and as a result, negative exchange interactions compete and the spin becomes fluctuated. Straighten it to become a spin glass magnetic material.

Furthermore, when the arrangement of different types of magnetic atoms in the oxide ferrimagnetic material is disordered, exchange interactions compete and the spin becomes frustrated, resulting in a spin glass magnetic material.

Alternatively, the film may consist of clusters of several tens to hundreds of OA that give a broad pattern similar to an amorphous state in X-ray diffraction, and the clusters are magnetically ordered, but there are magnetically long distances between the clusters. If order does not work, a spin glass state occurs.

Spin glass states cannot occur in ordered crystals. One way to achieve an imperfect state is to form a film on a room-temperature substrate and then not perform boss annealing.

The thin film may be amorphous or may contain microcrystals to the extent that it causes a broad pattern in X-ray diffraction.

Although the composition is not particularly limited, it is preferable to contain Co, since random anisotropy due to Co ions is effective when Co is contained as a constituent element. Co
The basic composition of ferrite is (Co, Fe), 0. However, it does not eliminate compositional deviations such as oxygen defects and additive components such as Zn and Ni. Co atoms are preferably contained in an amount of 10 at % or more, more preferably 30 to 70 at %.

A spin glass magnetic material made of a thin film with such a ferrite composition, especially a spin glass magnetic material with a Co ferrite composition, has a spin freezing temperature of around 300, which is significantly higher than that of conventional spin glass magnetic materials, which is about several tens of degrees. It is characterized by a high

It was also confirmed that this spin glass magnetic material with a ferrite composition exhibits a unique behavior that conventional spin glasses do not have when the magnetic susceptibility changes with temperature.

That is, the curve showing the temperature change in magnetic susceptibility has a plurality of maximum points. Although it is not clear that there is a direct relationship between having a plurality of maximum points and a high spin freezing temperature, it is one of the characteristics of the spin glass magnetic material of the present invention, and conversely, the spin glass magnetic material of the present invention It follows that a body can also be characterized by a curve showing a temperature change in magnetic susceptibility having a plurality of maximum points.

Next, a method for manufacturing such a spin glass magnetic material will be explained. The spin glass magnetic material according to the present invention can be manufactured using various thin film forming methods such as high frequency sputtering and ion beam sputtering. The case of manufacturing by ion beam sputtering method will be explained below.

First, raw materials such as oxides of constituent elements of the magnetic material or carbonates and nitrates that become oxides by firing, such as Fe203
, Co304, etc. in the desired ratio,
A sputtering target made of a sintered body is obtained by sintering. It goes without saying that the target is not limited to such a composite oxide target, but a metal target or a plurality of targets may be used.

This target is attached to a predetermined position in a sputtering device, and after the vacuum is evacuated to a degree of vacuum of 6×10−6 Torr or less, Ar gas is supplied to an ion gun, ionized and accelerated, and the target is sputtered.

Then, the sputtered secondary particles are deposited on a suitable substrate to form a thin film. At this time, it is desirable to introduce oxygen gas into the vicinity of the substrate to deposit the film in a reactive atmosphere.

Although the resulting film composition does not necessarily match the target composition, the film composition can be controlled by appropriately controlling the target composition. Furthermore, the amount of oxygen in the film changes slightly depending on the oxygen gas concentration at the time of formation, resulting in, for example, oxygen defects.

However, since it is sufficient to obtain a film exhibiting spin glass-like behavior, some oxygen defects can be tolerated.

(Example) The present invention will be explained in detail below.

Example-1 First, the production of spin glass magnetic material will be explained.

After sintering the oxide having the composition shown in Table 1, it was processed into a disk with a diameter of 3 inches, the surface was smoothed, and the disk was placed in a target holder in an ion beam sputtering device. A glass substrate was used as the substrate, and after the glass substrate was placed in a substrate holder, the pressure inside the chamber was reduced to 4×10−6 Torr. Then add 8" gas to the ion gun 2 x 10-
The oxygen gas was introduced to a temperature of 1.5 Torr, and oxygen gas was further flowed around the glass substrate at a flow rate of about 1.times.10 Torr. A Kaufmann type ion gun was used as the ion source, and Ar ions were
Sputtering was performed at an acceleration of keV.

Table 1 shows the spin freezing temperatures measured using a VSM (vibrating sample magnetometer) and 5QUID in addition to the target compositions used.

Note that for samples No. 1 and 1, the substrate temperature was set to room temperature;
, 2 to No. 13, the substrate temperature was 50°C.

In addition, the compositions listed in Table 1 are target compositions, but
It was confirmed that the thin film composition could almost reproduce the target composition, except for a slight deviation in oxygen content.

The X-ray diffraction results for CoFe2O4 of samples No. 1 are shown in FIG. The X-ray diffraction results for C0Fe2O4 of sample No. 2 are shown in FIG. As can be seen by comparing FIGS. 6 and 7, different results were obtained with respect to crystallinity depending on the sample.

FIG. 8 shows temperature changes in magnetization determined by 5QUID for samples No. 1. Further, the results for sample No. 12 are shown in FIG. In the figure, the curve indicated by FC represents the change in magnetization during cooling in a magnetic field, and ZFC represents the change in magnetization during cooling in no magnetic field. FC and ZFC
The temperature at which the difference in magnetization appears is the spin freezing temperature. It can be seen that both have very high spin freezing temperatures of over 300°C. In addition, as shown in Table 1, all spin glass magnetic materials made of thin films with ferrite compositions have high spin freezing temperatures, and it can be seen that the spin freezing temperatures are particularly high in the case of Co-containing ferrite compositions.

Further, FIG. 10 shows the temperature change in magnetic susceptibility for sample No. 1. From the same figure, 77K to 327
In the range of , a sharp peak near 86,
It can be seen that there is a very broad peak near 260. There has been no report of a spin glass magnetic material having two or more peaks in the temperature characteristics of magnetic susceptibility, and this is the first finding by the present inventors.

Below are the margins in Table 1. Example-2 A CoFe2O4 amorphous thin film was used as the recording layer, and this amorphous C was deposited on a glass substrate.

A ferrite film was formed, and an Aj7 sputter film was further formed as a reflective film to form a magnetic recording medium.

As shown in Fig. 2, the irradiated area of the recording layer is heated to a temperature above the spin freezing temperature (T, ) by local heating using a semiconductor laser with an output of 5 mW, and then cooled without applying a magnetic field to Z
The FCFC area was established. Subsequently, after similar laser irradiation, 1
The FC region was created by cooling while applying a magnetic field of 00e.

Next, when laser light was incident on the substrate side and the light reflected on the reflective layer was measured, a significant difference in the Faraday rotation angle was observed between the ZFCFC region C region and the fact that it could be used satisfactorily as a magnetic recording medium. Ta.

Example-3 An example using the recording medium shown in FIG. 3 is shown.

As the recording layer, an amorphous Co ferrite thin film similar to that in Example 2 was used, and as a bias layer, Sl (Coo
, 6 Cuo, 3 Feo, l) b, s A magnetic recording medium was constructed using a thin film (perpendicularly magnetized film with a coercive force of 5000 e).

As shown in Fig. 3, the irradiated area of the recording layer is heated to a temperature above the spin freezing temperature (T,) by local heating treatment using a semiconductor laser with an output of 5 mW, and then cooled without applying a magnetic field.
The FCFC area was established. Subsequently, the irradiated portion of the recording layer was heated to T7 or higher by local heat treatment using a semiconductor laser with an output of 5IIIν, and then cooled while applying a magnetic field of 1 koe.
Created FC area.

Next, when laser light was incident on the substrate side and the light reflected on the reflective layer was measured, a significant difference in the Faraday rotation angle was observed between the ZFCFC region C region and the fact that it could be used satisfactorily as a magnetic recording medium. Ta.

Moreover, the recorded information did not disappear even after two months and was well preserved.

Although the bias layer that can be used in Example-3 is not limited to this, the Ss-based thin film is suitable for multilevel recording because the value of the bias magnetic field generated changes depending on the magnitude of the external magnetic field. suitable for Also 511 (
Coo, b Cuo, 3 Feo, l) b,
The first diagram shows the dependence of the magnetization curve of s on the external magnetic field. As can be seen from Figure 11, if such a bias layer is used, a large difference in residual magnetic field can be obtained with a small difference in external magnetic field ((a)>(b)>(e
), the magnetization state of the recording layer can be changed with a small modulation magnetic field, which is advantageous for high-speed modulation.

Note that any material whose magnetization changes depending on the presence or absence of a magnetic field during cooling, such as spin glass, can be used in the recording medium of the present invention.

[Effects of the Invention] As explained above, according to the present invention, it is possible to obtain a new magnetic recording device that is capable of non-contact recording and reproduction, easily overriding, and capable of multilevel recording. . In addition, it is a new discovery that a thin film with a ferrite composition is a spin glass magnetic material, and its spin freezing temperature is high, especially extremely high in a system containing Co. This makes it possible to actually apply spin glass magnetic materials. The industrial value of the invention is great.

[Brief explanation of drawings]

Figures 1, 5, 8 and 9 are characteristic diagrams showing the temperature characteristics of magnetization of spin glass magnetic materials, and Figures 2, 3 and 4 are magnetic diagrams for explaining the present invention. 6 and 7 are X-ray diffraction diagrams, FIG. 10 is a temperature characteristic diagram of magnetic susceptibility, and FIG. 11 is a characteristic diagram of a bias layer.

Claims (8)

[Claims] (1) A magnetic recording medium comprising a spin glass magnetic layer as a magnetic recording layer on a substrate. (2) The magnetic recording medium according to claim 1, further comprising a bias layer for applying a bias magnetic field to the spin glass magnetic layer. (3) The spin glass magnetic material according to claim 1 or 2 is C.
o A magnetic recording medium comprising a thin film having a ferrite composition. (4) Using the magnetic recording medium according to any one of claims 1 to 3, a heating means for heating the spin glass magnetic body to a temperature equal to or higher than the spin freezing temperature, and a magnetic field applied to the spin glass magnetic body when cooling the spin glass magnetic body have at least two values. A magnetic recording device characterized by comprising: magnetic field generating means for causing the above change. (5) A spin glass magnetic material characterized by being made of a thin film having a ferrite composition. (6) Spin glass magnetic material having an amorphous or microcrystalline ferrite composition. (7) A spin glass magnetic material characterized by having a plurality of maximum points on a temperature characteristic curve of magnetization. (8) The spin glass magnetic material according to any one of claims 5 to 7, characterized in that it has a ferrite composition containing Co.