JPH01152603A - Oxide magnetic thin film - Google Patents

Abstract

PURPOSE:To obtain an oxide magnetic thin film which is superb in the formation of film by using a material where one part of Fe is substituted with vanadium. CONSTITUTION:An oxide magnetic thin film has a composition which is expressed by a general expression COxVyFe3-x-yO4-delta (wherein 0.7<=x<=1.1, 0.24<=y<=0.5, 0<=delta<=1). In the production method, as for vapor growth method, it includes the vacuum deposition method, cluster ion beam method, sputtering method, ion plating method, CVD method, and plasma flame spraying method, while the moisture growth method includes the ferrite plating method. Vertical axis of easy magnetization is improved and stress for favorably generating magnetic distortion introducing anisotropy efficiently operates. Also, by setting the ratio of metal to oxygen of cobalt ferrite to 1:1-3:4, the Coercive force as well as the rectangular ratio can be further improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an oxide magnetic thin film suitable as a magneto-optical recording material.

[Summary of the invention]

The present invention is used as a magneto-optical recording material, with the general formula CO
g V y Fe ff-x-y By specifying the composition ratio of the oxide magnetic thin film represented by Oa-6, an excellent perpendicular magnetization film can be easily obtained, and an oxide magnetic film with excellent film formability can be obtained. The aim is to provide a thin film.

[Conventional technology]

Conventionally, thin films of rare earth-transition metal alloys such as Tb-Fe alloys having large perpendicular magnetic anisotropy have been the mainstream as magnetic materials constituting magneto-optical recording media.

However, although the above-mentioned rare earth-transition metal alloy thin film has excellent magneto-optical properties, it lacks corrosion resistance and is easily corroded, and cannot be put into practical use unless auxiliary means such as forming a protective film on the alloy thin film are used. Currently, it cannot be used as a

In contrast to rare earth-transition metal alloy thin films that lack corrosion resistance, in recent years oxide magnetic thin films that have excellent corrosion resistance have been used as magnetic materials constituting magneto-optical recording media. A lot of research is being conducted into this possibility.

The above oxide magnetic thin film is iron/garnet.

Typical materials include barium ferrite and cobalt ferrite.

Among these materials, oxides mainly composed of cobalt ferrite are preferred because they have various excellent characteristics such as being able to form films at relatively low temperatures and having a high Faraday rotation ability of 3 to 4 degrees/μm. Magnetic materials are attracting attention.

The crystalline system of oxide magnetic thin films such as the above-mentioned cobalt ferrite is cubic (spinel structure), so in order for the oxide magnetic thin film to obtain perpendicular magnetic anisotropy, it is caused by applying a large stress to the film. It is necessary to utilize magnetostriction-induced anisotropy. The material composition of the oxide magnetic thin film on which the stress that produces the magnetostriction-induced anisotropy is effectively applied has not yet been fully elucidated. A lot of research is being carried out from all directions.

Under these circumstances, an oxide magnetic thin film has been proposed in which, for example, a part of Fe in an oxide magnetic material mainly composed of cobalt ferrite is replaced with metal ions such as chromium or aluminum.

[Problem that the invention seeks to solve]

However, as mentioned above, even with an oxide magnetic thin film in which a part of the Pe in an oxide magnetic material mainly composed of cobalt ferrite is replaced with a metal such as chromium or aluminum, the stress that causes magnetostriction-induced anisotropy to occur satisfactorily. Not enough has been done to make it work effectively.

Therefore, the present invention was proposed in order to satisfy the above-mentioned conventional requirements, and the present invention was developed by examining various elements to be added and substituted for the basic composition consisting of cobalt ferrite. The object of the present invention is to provide an oxide magnetic thin film that can easily be obtained with perpendicular magnetization and has excellent film formability.

[Means for solving problems]

In order to achieve the above-mentioned purpose, the present inventors have conducted extensive research and have discovered that cobalt ferrite (Co) has a spinel structure.
It has been found that a material in which a part of Fe, which is a metal element constituting FegOn), is replaced with vanadium (V) can easily form an excellent perpendicular magnetization film. In addition, cobalt
The amount of oxygen that makes up ferrite (Codexes) is
The inventors have also discovered that excellent magnetic properties can be exhibited by setting the spinel phase compound to a stoichiometric composition or less than the stoichiometric composition.

The present invention has been made based on the above findings, and the oxide magnetic thin film according to the present invention has the general formula COzVyF e
5-x-yOa-δ (0.7≦x≦1.1.0
．． 24≦y≦0.5.0≦δ≦1).

Here, the reason why a part of Fe constituting the cobalt ferrite is replaced with some element is to improve the ease of perpendicular magnetization of the oxide magnetic thin film by reducing the saturation magnetic flux density. However, when a part of cobalt ferrite is normally replaced with such an element, magnetostriction, which is a measure of the ease with which perpendicular magnetization anisotropy occurs, also tends to decrease at the same time.

The larger the magnetostriction value, the more perpendicular magnetization tends to occur. Therefore, it is necessary to replace a portion of the cobalt ferrite with an element that can reduce the saturation magnetic flux density but does not reduce the magnetostriction.

The present inventors adopted vanadium as an excellent substitution element having the above-mentioned properties. That is, it was discovered that vanadium is an element that satisfies the contradictory requirements of reducing saturation magnetic flux density and not reducing magnetostriction in a well-balanced manner by substituting a part of Fe constituting cobalt ferrite.

In addition, cobalt ferrite that has been partially replaced with vanadium has an excellent squareness ratio, and vanadium has various excellent properties such as excellent magnetic anisotropy even with a small amount of addition. It has been clarified through experiments by the present inventors that this effect is exhibited.

Here, the composition y of vanadium constituting the oxide magnetic thin film according to the present invention is preferably 0.24 or more and 0.5 or less. If the composition y of vanadium is less than 0.24, the magnetization becomes large. This is because if the vanadium composition y exceeds 0.5, the magnetostriction decreases, the perpendicular magnetization anisotropy becomes small, and a good squareness ratio cannot be obtained. This is because Considering that in the past, when aluminum or chromium was used as an additive element, the amount of the additive element was 0.5 or more, it can be said that the amount of vanadium added is extremely small.

On the other hand, the composition X of cobalt constituting the oxide magnetic thin film is
It is preferably 0.7 or more and 1.1 or less.

If the cobalt composition is less than 0.7 (in the direction in which the Fe content increases), the Faraday rotation ability will decrease, which is undesirable, and if the cobalt composition exceeds 1.1, the magnetization and coercive force will decrease. This is because both decrease, resulting in deterioration of magnetic properties.

In addition, δ of the oxygen amount 4−δ constituting the oxide magnetic thin film is 0
It is preferable that the composition ratio of the metal element to oxygen be in the range of ≦δ≦1, that is, the composition ratio of the metal element to oxygen is in the range of 3:4 (spinel phase) to 1:1 (wüstite phase).

To set the composition ratio of metal element and oxygen to 3:4 to 1:1,
By actively changing the amount of oxygen introduced when forming an oxide magnetic thin film, the oxygen contained in the above composition can be changed, and if the oxide magnetic thin film falls within this composition range, it can be maintained. It is possible to form an oxide magnetic thin film with a high magnetic force and a good squareness ratio that exhibits perpendicular magnetization anisotropy.

If the oxide magnetic thin film satisfies the above composition,
Stress that satisfactorily produces magnetostriction-induced anisotropy acts effectively.

As a method for producing the oxide magnetic thin film having the above-mentioned composition, a vapor phase growth method, a wet growth method, or the like can be applied. The above vapor phase growth methods include vacuum evaporation method, cluster growth method,
Ion beam method, sputtering method, ion blating method, CVD method.

Examples include plasma spraying. In addition, examples of the wet growth method include the ferrite-metsuki method.

Co, VyF e 5-x-yo*- according to the present invention
δ (However, 0.7≦x≦1.1, 0.24≦y≦0.
5, O≦δ≦1) The oxide magnetic thin film has negative magnetostriction. Therefore, by applying tensile stress, it is possible to obtain preferable perpendicular magnetic anisotropy in the perpendicularly magnetized film. As a means of applying tensile stress, a thin film is prepared at high temperature on a substrate made of a material having a thermal expansion coefficient α of α≦70 x 10-'(K-'), and when the film is cooled to room temperature. Examples include methods that utilize thermal stress.

The thickness of the above-mentioned oxide magnetic thin film is not prescribed in any way, and may be set appropriately depending on the desired characteristics, etc., but it is preferably about 0.4 μm. This is the thickness required when a magnetic thin film is produced, and if it is too thick, the characteristics as an optical recording medium will deteriorate.

Furthermore, there is a tendency that the lower the Curie temperature of an oxide magnetic thin film, the better the magnetic properties, and the better the properties such as perpendicular magnetization anisotropy. The Curie temperature when a part of the cobalt ferrite is not replaced by a substitution element is 520℃
However, even when this is replaced with vanadium, its Curie temperature does not decrease much at 480°C to 500°C.
Therefore, in order to lower the Curie temperature and further improve properties such as perpendicular magnetization anisotropy, a part of F”e was
It may be replaced with an additional element. In this case, the replaceable third
The elements include Al, Ga, Ru, and Ti.

Rh, Mn, Ni, Zn, Sn, Cr, Cu, Mg.

In, Sb, Sc, Bi, Y, Sm, Eu, Tb.

Examples include Gd.

[Effect]

Vanadium, which is used as an element to partially replace Fe constituting cobalt ferrite, has an excellent effect of reducing saturation magnetic flux density, but tends not to reduce magnetostriction much. Therefore, in an oxide magnetic thin film in which a part of the Fe constituting cobalt ferrite is replaced with vanadium, the perpendicular magnetization ease is improved, and the stress that favorably produces magnetostriction-induced anisotropy acts effectively. .

Furthermore, by setting the metal to oxygen ratio of the cobalt ferrite constituting the oxide magnetic thin film according to the present invention within the range of 1:1 to 3:4, even better coercive force and squareness ratio can be obtained. This becomes a perpendicular magnetic FLL film.

〔Example〕

Examples of the present invention will be described below with reference to the drawings, but the present invention is not limited to these examples.

First, Co, V, and Pe were adjusted and melted, and the composition after sputtering was Coo, ++Vo, sPe+, 70
A metal alloy target was prepared with a spinel-type cobalt ferrite as a target of 4-δ. The diameter of the prepared target was 75 mm.

Using this cobalt-ferrite alloy target, an oxide magnetic thin film was deposited on a quartz glass substrate by a reactive sputtering method at room temperature while introducing Ar and O2 gases using a high-frequency magnetron sputtering device to form a sample thin film. Created. At this time, the input power is 30
0W, gas pressure 6++Torr, 0! The flow rate of 2.
Change it from 5 SCCM to 3.2 SCCM and adjust the Ar flow rate until the Ar and 0□0 total flow rate is 203CC? Samples A to H were obtained in such a way that The thickness of the thin film produced in this case was 0.43 μm.

The relationship between 01 flow rate and deposition rate is as shown in Figure 1.
When the flow rate of 02 is low, a metallic film is deposited and the deposition rate is not very high, and as the flow rate of Ol is high (the deposition rate increases due to the formation of oxides, and
As the flow rate increases, an oxide film with a low sputtering rate is formed on the target surface, and the deposition rate decreases again.

-a, when producing a ferrite thin film by reaction sputtering, a good thin film can be obtained from the maximum deposition rate to the side where the 02 flow rate is high. However, in systems containing aluminum and chromium, which were conventionally added as additive elements, since the oxides of these elements have extremely low sputtering rates, the deposition rate changes significantly with increasing flow rate of 0□, making it difficult to produce a good thin film. The conditions were limited to a very narrow area. On the other hand, since vanadium, which is used as an additive element in the oxide magnetic thin film according to the present invention, has a not so small sputtering rate, the film can be formed under a moderately wide range of conditions, and it also has excellent reproducibility. Are better.

Samples A to H obtained as described above were heat treated in the atmosphere at 500°C for 2 hours, and as a result, six types of samples, Samples C to H, exhibited magnetism. Ta.

・ Figure 2 shows the Faraday rotation powers measured at a wavelength of 780 nm for these six types of samples, and the maximum magnetic field 1QkQ
The squareness ratios calculated from the Faraday loops measured at e are shown in FIG. Note that unlike the Kerr loop, the Faraday loop has a small optical enhancement effect, and the shape of the hysteresis loop is similar to that of a vibrating sample magnetometer (VS
It almost coincides with the magnetization curve measured in M). The squareness ratio was determined by the following formula.

As is clear from FIG. 3 above, the sample with the highest squareness ratio and excellent as a perpendicular magnetization film had a squareness ratio of 80%. The composition determined by electron probe X-ray diffraction (EPMA) for the above sample is Coo,
, ovo, 4+Fe+, hqoa-6, and the metal composition ratio is slightly different from the target composition.

Although we did not quantify the amount of oxygen in each of the fabricated samples A to H, it is clear from Figure 2 that in this oxygen content region, the thin film consists of a mixture of the nonmagnetic wustite phase and the ferrimagnetic spinel phase. Therefore, if we consider that the proportion of spinel phase increases as the amount of oxygen increases, we can explain the changes in Faraday rotation ability and squareness ratio. That is, the Faraday rotation ability takes a maximum value of 2.9 deg/pm at an oxygen supply rate of 3.1 SCCM. This is considered to indicate that this sample has the electrical specific composition closest to that of the spinel phase (metal:oxygen-3;4). On the other hand, in 3.2 SCCM, where the oxygen supply amount is even higher, the Faraday rotation ability becomes less than 2 deg/μm again, and the squareness ratio and coercive force H
c is drastically reduced. Since the XwA diffraction also became weaker at this time, it is thought that this change in magnetic properties was caused by the collapse of spinel phase crystals due to excess oxygen. Furthermore, it is considered that Sample A and Sample B, which were not magnetized at all, had a composition close to that of the nonmagnetic wustite phase (metal:oxygen=1:1). Furthermore, the sample exhibiting the best squareness ratio of 80% was produced under a lower oxygen supply than sample G, which is considered to have a spinel phase-stuck composition. Considering the above, it can be said that a sample exhibiting a good squareness ratio can be obtained with an oxygen composition intermediate between the wustite phase composition and the spinel phase composition. Therefore, the coercive force H
It can be said that a composition with a large c (and a good squareness ratio) has a range of δ in the general composition formula within the range of 0≦δ≦1.

2-3. 1 to 4 Similar studies were conducted using alloy targets with different composition ratios in Example 2. Example 3. Comparative Examples 1 to 4 were conducted.

In addition, as Comparative Example 5, an experiment was also conducted on a sample in which vanadium was not added. The results are shown in Tables 1 and 2.

(The following is a blank space) The regions of the thin film composition ratios listed in Tables 1 and 2 above are indicated by diagonal lines in FIG. In addition, Fig. 4 shows Co and V.

FegOa-a (x + 3' + z = 3)
It is a ternary composition diagram when expressed as . In addition, in Fig. 4, the ■ mark is for Example 1, the ■ mark is for Example 2, and the ■ mark is for Example 3.
The ■ mark corresponds to Comparative Example 1, the ■ mark corresponds to Comparative Example 2, the ■ mark corresponds to Comparative Example 3, the ■ mark corresponds to Comparative Example 4, and the ■ mark corresponds to Comparative Example 5.

In addition, FIGS. 5A to 5H show typical magnetization curves for the compositions of Examples 1 to 3 and Comparative Examples 1 to 5. B, FIG. 5C1 In FIG. 5H, a represents the magnetization curve in the perpendicular direction, and b represents the magnetization curve in the in-plane direction. Moreover, FIGS. 5D to 5G all show magnetization curves in the vertical direction.

As is clear from Tables 1 to 2, Figure 4, and Figures 5A to 5H, magnetostriction decreases in the composition side containing more vanadium than the region indicated by the thick line frame, resulting in magnetic anisotropy. If the composition contains less vanadium, the magnetization becomes too large to form a perpendicularly magnetized film, and if the composition contains a lot of cobalt, both magnetization and coercive force tend to decrease, and if the composition contains a lot of ferrite. Faraday rotation ability tends to decrease on the composition side where Therefore, the composition of an excellent oxide magnetic thin film that can obtain a squareness ratio of 70% or more in the perpendicular magnetization curve is C:o,V.

F 135-x-yo4-δ (0.7≦x≦1
．． 1.0.24≦y≦0.5, O≦δ≦1) is preferable.

To summarize the above results, the characteristics of the oxide magnetic thin film according to the present invention are as follows.

Saturation magnetic flux density Bs = 3 to 4.2 kG Faraday rotational power θr = 1.2 to 2.4@/μm Light absorption α = 3.6 μm −' Refractive index n = 2.6 Figure of merit 2θF/α = 0.7 ~1.3' Note that regarding the Curie temperature Tc, the oxide magnetic material according to the present invention has a Curie temperature Tc of 4
The temperature ranged from 80°C to 500°C, which was not much lower than the Curie temperature Tc of 520°C for the unsubstituted material. In oxide magnetic materials, there is a tendency that the lower the Curie temperature Tc, the better the characteristics. Therefore, a fourth metal additive element such as gallium or aluminum is added to the composition of the oxide magnetic material according to the present invention to improve the characteristics of the oxide magnetic material. It may be added within a range that does not cause deterioration.

〔Effect of the invention〕

As is clear from the above description, the oxide magnetic thin film according to the present invention has a part of the Fe constituting the cobalt ferrite replaced with vanadium, so it exhibits excellent effects even with a small amount of substitution. Since the saturation magnetic flux density is reduced without reducing magnetostriction, it is possible to easily manufacture an oxide magnetic thin film.

Further, since vanadium has the effect of appropriately widening the film forming conditions, it is possible to easily produce a ferrite film by reactive sputtering and to have excellent reproducibility.

Therefore, it is possible to provide an oxide magnetic thin film that exhibits excellent properties as a magneto-optical recording material.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram showing the relationship between the oxygen flow rate during sputtering and the thin film deposition rate. FIG. 2 is a characteristic diagram showing the relationship between oxygen flow rate and Faraday rotation ability during sputtering. FIG. 3 is a characteristic diagram showing the relationship between oxygen flow rate and squareness ratio during sputtering. FIG. 4 is a ternary composition diagram showing the composition range of the oxide magnetic thin film according to the present invention. 5A to 5H show typical magnetization characteristic diagrams in Examples 1 to 3 and Comparative Examples 1 to 5, respectively. Patent Applicant Sony Corporation Representative Patent Attorney Kowa Akioka Kyuzai Sakae Sato Masaru 02 it (SCCM) Cao Cox○46 Sei ω Yamagata Ratio (7゜)

Claims (1)

[Claims] General formula, Co_xV_yFe_3_-_x_-_yO_4_-_
δ (However, 0.7≦x≦1.1, 0.24≦y≦0.
5. An oxide magnetic thin film having a composition expressed by 0≦δ≦1).