JPH01315108A - Mn-al ferromagnetic-substance thin film and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain an Mn-Al ferromagnetic-substance thin film which has a phase tau inside the whole film and whose spontaneous magnetization is equal to that of a bulk alloy in such a way that an amount ratio of Mn in an Mn-Al film is nearly definite in a face direction of the film and is changed in a film- thickness direction within a specific range. CONSTITUTION:A thin film 11 on a substrate 12 is constituted in such a way that films containing a larger amount of Mn and films containing a larger amount of Al are laminated alternately. An amount ratio of Mn in this Mn-Al film 11 is nearly definite in a face direction of the film 11; when, in this thin film 11, the amount ratio of Mn is changed artificially in a film-thickness direction within a range of 45 to 65 atomic %, a phase tau can be formed preferentially. By this setup, it is possible to obtain an Mn-Al ferromagnetic-substance thin film whose spontaneous magnetization is equal to that of a bulk alloy.

Description

[Detailed Description of the Invention] [Industrial Application Field 1] The present invention relates to an alloy thin film of manganese and aluminum,
In particular, the present invention relates to a film suitable for generating large spontaneous magnetization and magnetic anisotropy equivalent to that of bulk alloys.

[Prior art] It is known that an alloy of manganese (M n ) and aluminum (A Q ) becomes a ferromagnetic material when it has a certain crystal structure, and its bulk crystal is applied to permanent magnets, etc. . In recent years, attempts have been made to make this material thinner.

Examples include Journal of Applied Physics, 61 (1987), pp. 4281-428.
3 pages (J, Appil.

Phys, 61 (1987), pp, 4281-42
M formed by the sputtering method discussed in 83)
In the n-A12 alloy film, the Mn to AflO ratio is constant within the film.

[Problems to be Solved by the Invention] In the above-mentioned conventional technology, even if the film formation conditions are variously changed, the spontaneous magnetization of the obtained film is only 120 emu at the maximum.
/cc, which is only 1/48 degree of that of the bulk alloy.

The reason for this is that even though the ratio of Mn and Al is constant, the obtained film contains a structure that generates ferromagnetism (τ phase) as well as a non-magnetic structure (ε phase).

A first object of the present invention is to obtain a Mn-AQ ferromagnetic thin film that has a phase in the metal body within the film and has spontaneous magnetization equivalent to that of a bulk alloy.

Furthermore, magnetic anisotropy is also an important property in magnetic devices; for example, in perpendicular magnetic recording, anisotropy in the direction perpendicular to the film is essential.

A second object of the present invention is to generate magnetic anisotropy that could not be obtained with the above-mentioned prior art.

[Means for Solving the Problems] The first object of the present invention is to
The quantitative ratio of n is approximately constant in the plane direction of the film, and 45
M n fluctuating in the film thickness direction within a range of -65 at%
-Achieved by producing a Q film.

A second object of the present invention is that the Mn content ratio in the Mn--Al film is approximately constant in the plane direction of the film.

By producing an Mn-Al film in which the Mn content ratio varies in the film thickness direction and is within the range of 45-65 at% in at least a portion of the film thickness direction. It can be achieved.

[Action 1] The circumstances leading to the achievement of the first object of the present invention are as follows.

The reason why the spontaneous magnetization is small in the above conventional technology is that the phase is in a metastable state due to the ferromagnetic structure.
We searched for conditions under which the τ phase occurs more stably than the ε phase.

One of them is various M n -A with different spontaneous magnetization.
The Q alloy was cut and the composition of the cross section was examined microscopically. As a result, it was found that those with large spontaneous magnetization are composed of only the phase, and those with /jf and three small spontaneous magnetizations are composed of a mixture of τ and ε phases. When the composition of the region where this τ phase exists was investigated, it was found that the molar ratio of Mn in the τ phase was 45 to 65 at %, and the composition varied.

From the above findings, even in thin films, the Mn content ratio is 45 to 6.
It was predicted that a large spontaneous magnetization would be obtained by preferentially forming the τ phase by artificially varying the composition within a range of 5 at %, and an attempt was made to realize the above composition variation using thin film lamination technology.

That is, we thought that if Mn and Al were alternately layered on a substrate by vacuum evaporation or the like and these two elements of Mn and Al were diffused into each other, the Mn content ratio would vary in the thickness direction of the film.

Based on this idea, various thin films with different variations in the Mn ratio were fabricated using the deposition rate, deposition time, and substrate heating temperature as parameters.

The structure of the produced thin film is as shown in FIG. 1(a).
It has a structure in which films with a large amount of n and films with a large amount of Af1 are alternately stacked.

Moreover, the distribution of the Mn content ratio in the film thickness direction of this thin film is the first
It is as shown in figure (b). FIG. 1(b) shows the variation in the Mn content ratio in a state in which a film with a large (excessive) Mn content and a film with a large (excessive) Al content are laminated. The quantitative ratio of Al is 100 at % minus the quantitative ratio of Mn. The range of variation in the Mn ratio is from 0 to 100.

In regions a and b, even if mutual diffusion of Mn and Al occurs, M
This is a region where n and Al do not mix and pure Mn and Al remain. Regions C and d are regions where mutual diffusion of Mn and Al occurs, and the quantitative ratio of Mn gradually changes. If the layer thickness is thin, the interdiffusion of Mn and Al will cover the entire region of the Mn layer and the Al layer, and as a result, the regions a and b will not exist, and only the composition variation regions of C and d will exist. The distribution of the Mn content ratio in the film thickness direction in this case is shown in FIG. 1(c). The variation range of the Mn content ratio is from X to X2.

Figure 8 shows the deposition conditions of the thin film produced in the examples described later, Mn
Magnetic properties such as distribution of quantity ratio and spontaneous magnetization are shown.

In the thin film of sample No. 1-11, the spontaneous magnetization is 450 em
It is u/cc. This value is equal to the value of the spontaneous magnetization of the bulk alloy. Therefore, it can be seen that a thin film that achieves the first object of the present invention has been realized.

At this time, the smallest value among the minimum values X□ of the Mn content ratio is 45 at% for sample No. 093, and the largest value among the maximum values X2 is 65 at% for sample No. 6.7. Therefore, the variation range of Mn content ratio is 45-65 at
%. Furthermore, even if the number of laminated layers is varied in the range of 50 to 1000, a spontaneous magnetization of 430 emu/cC can be obtained, and even if the period is varied in the range of 8 to 20, a spontaneous magnetization of 450 emu/c can be obtained.
A spontaneous magnetization of c was obtained. Therefore, it can be seen that spontaneous magnetization equal to that of the bulk alloy can be obtained even if films having various structures with different product jn numbers and periods are produced. moreover,
In the structure of sample No. 11, the period and the minimum and maximum values of the Mn content ratio take random values in the film thickness direction. In the sample with such a structure, the spontaneous magnetization is 450 emu/cc, as in the sample in which the three parameters listed in L are constant.

Therefore, if the Mn content ratio is within the range of 45 to 65 at%, even if the film has a structure in which the number of stacked layers, period, and minimum and maximum values of the Mn content ratio are different, the spontaneous magnetization will be the same as that of the bulk alloy. You can see what you can get.

In addition, in sample No. 12, the spontaneous magnetization of the film was 10
100e/cc, which is smaller than bulk alloys. The reason for this is thought to be that the Mn content ratio of this film varies in the range of O to 100 at%.

The quantitative ratio of Mn, which is a part of this film, is 45 to 65 at%
In the region of
Since the ε phase is formed in a region where the proportion of . The spontaneous magnetization of the film is the average value of the values in these regions. In this sample, the τ phase region and the ε phase region exist at a film thickness ratio of 1=3, so the average value of spontaneous magnetization is 450X1/(1
+3)=112 emu/cc. This value roughly matches the above-mentioned 10100e/cc. This also shows that the condition for generating ferromagnetism is to keep the Mn content ratio within the range of 45 to 65 at%.

Next, the operation of the means for achieving the second object of the present invention will be explained.

As can be seen from FIG. 8, an anisotropic magnetic field was generated in all the samples, indicating that a thin film that achieved the second object of the present invention was realized.

In particular, in sample No. 12, the anisotropic magnetic field value was 60,000.
e and large.

In addition, in this sample, the value of spontaneous magnetization is 100 emu/c
c and small. However, it can be used for magneto-optical recording media and the like.

The above two samples are characterized by a large rate of change in the Mn content ratio. This can be seen from the fact that the rate of change in the Mn content ratio and the anisotropic magnetic field are in a proportional relationship in all the samples shown in FIG.

One method for producing the M n -A Q ferromagnetic thin film of the present invention is to alternately deposit Mn and Al on a substrate while heating the substrate at 200-350° C. in vacuum. As the substrate, a (100)-plane NaCl type single crystal is preferred, and a (101-plane Mg◯ single crystal is particularly preferred).

Generally, the film is formed at a low temperature around room temperature.

Crystal disorder is large and good characteristics cannot be obtained.

In a ferromagnetic thin film, there are effects such as a decrease in spontaneous magnetization, anisotropic magnetic field, etc. On the other hand, if the temperature during film formation is too high, adverse effects such as changes in film composition will occur. For example, when depositing various elements with different saturated vapor pressures, if the substrate temperature is too high, the elements with high saturated vapor pressures will reevaporate from the substrate during deposition, making it impossible to obtain the desired composition.

In the M n -A Q thin film of the present invention, as is clear from the results shown in FIG. 8, good results are obtained by heating the substrate to 200° C. to 350° C. to form the film.

In addition, in the examples, Mn was deposited first.

When Afl is deposited first, the spontaneous magnetization and anisotropic magnetic field are slightly inferior to those of the example, but compared to the conventional M n
-A It has been confirmed that it is superior to Q thin film.

[Example] Example 1゜ Embodiment 1 of the present invention is shown in FIGS. 2 and 3 (a).

This will be explained using (b).

In this example, an electron beam evaporation apparatus shown in FIG. 2 was used. Two electron gun heating devices 1 are placed in a vacuum chamber 5, and manganese (Mn) and aluminum (Al) are placed in the 2o of each electron gun heating device and heated.
Both are deposited simultaneously under a vacuum of 10-' Torr. In this state, by alternately opening and closing the two shutters 2, Mn and Al are deposited alternately on the glass substrate 12 attached to the stage 4 in the order of Mn and Afl. In sample 1, the coating speed was 0.5 per second in both cases.
A person opened and closed the shutter every 10 seconds.

Therefore, by opening the shutter once, a layer equivalent to the thickness of five people is deposited. The substrate temperature was kept at 250°C and
! Laminated.

The cross-sectional structure of the film of sample 1 and the composition change in the film thickness direction are shown in FIGS. 3(a) and 3(b), respectively. If the thickness of the deposited layer is 5 mm, the interdiffusion of Mn and Al will cover the entire region of the Mn layer and the Al layer, and as a result, only the region where the composition has varied in thickness will exist.

The variation rate of the Mn content ratio in this region is as follows: The maximum value of the Mn content ratio is 54 at% and the minimum value is 46 at%.
(54 [at%] -46 [at, %]) 15 (person) = 1.6 [at%/person].As a result of measuring the magnetic properties of this film, the spontaneous magnetization of the film was found to be different from that of the bulk alloy. Equivalent 450emu
/cc, and the anisotropic magnetic field was 140,008.

Furthermore, various films were fabricated using different film formation conditions.

The film forming conditions that were changed were the substrate temperature during fabrication, Mn and Al
shutter opening time, vapor deposition rate R, and number of stacked layers N. FIG. 8 shows the film forming conditions for the prepared samples Nos. 2 to 10. The distribution of Mn composition and the two vapor characteristics of anisotropic magnetic field and spontaneous magnetization in these samples are also shown in Figure 8. In sample No. 6-8, the substrate was a (100)-plane Mg○ single crystal. , and glass in other samples. On these two types of substrates, M
M n and Al1 by opening and closing the shutter 2.

They were applied alternately in the order of 80. Deposition rate is 0.5 people/s
ec and 1 person/sec, and the shutter opening time is 8~
The range is 12 seconds.

The distribution of the Mn content ratio in the film thickness direction is determined by the substrate quality, shutter opening time, and vapor deposition rate.

2 to ]-0 as well, the interdiffusion of Mn and Al extends to the region of the Mn layer and the Al layer, and as a result, only the region where the two compositions have changed exists. The width of this region of compositional variation, ie, the values of C and d in FIG. 1(c), ranges from 4 to 6 for these samples. Moreover, the Mn content ratio was within the range of 45 to 65 at% in all samples. The spontaneous magnetization of these samples No. 2-10 was 450 emu.
/cc, which was the same value as the bulk alloy. In addition,
As is clear from the comparison between Sample 1 and Sample 2 and between Sample 6 and Sample 7, the value of the spontaneous magnetization of the film did not change even if the number of stacked layers was changed.

The anisotropic magnetic field of samples No. 2 to 10 ranges from 3000e to 22000e as shown in FIG. This is proportional to the Mn content change rate shown in the figure. Therefore, by selecting film-forming conditions that increase the rate of change in Mn content, an improvement in the anisotropic magnetic field can be expected.

Example 2 A second example of the present invention will be explained with reference to FIGS. 4(a) and 4(b). Sample No. shown in this example.

No. 11 was produced using the electron beam evaporation apparatus shown in FIG.

On the glass substrate 12, the vapor deposition rate of Mn and An is 0.5.
Mn and An at a substrate temperature of 250℃
A total of 100 ON layers were deposited alternately in this order. Further, in this example, the deposition times of Mn and Al were randomly changed. For this reason, the shutter opening time should be changed from 10 seconds to 12 seconds in the case of Mn.
The time was varied in the range of seconds, and in the case of A11l, it was varied in the range of 8 to 10 seconds.

As a result, as shown in FIG. 4(a), a ferromagnetic film is produced in which Mn-excess layers and Al-excess layers are alternately laminated.

At this time, the film thicknesses of each layer are not equal, unlike in the first embodiment. Furthermore, as shown in FIG. 4(b), the maximum and minimum values of the Mn content ratio are also not constant, unlike in Example 1. The maximum value of the Mn content ratio is 58 at%, and the minimum value is 46 at%.

It was found that the ferromagnetic film of this example had a spontaneous magnetization of 450 emu/cc. This value is comparable to that of bulk alloys. Further, the anisotropic magnetic field was 10,000e.

Example 3゜Example 3, which was carried out to make magnetic anisotropy appear, was repeated in the fifth example.
This will be explained with reference to FIG. 5(a) and FIG. 5(b). Since magnetic anisotropy is related to symmetry, it increases as the composition change increases. From this point of view, the film forming conditions were selected for sample No. 12, and as shown in FIG. 5(b), the Mn ratio was 0.
It had a steep structure varying from at% to 1ooat%. Figure 5(a) shows excess Mn and Al produced under these conditions.
A superlattice structure film 11 consisting of an excess of layers is deposited on a glass substrate 12 with each layer having a thickness of 20 angstroms and a thickness of 1,000 angstroms.
The layers are laminated.

The manufacturing method will be explained below. The electron beam evaporation apparatus shown in FIG. 2 was used as the evaporation apparatus. On the glass substrate 12, M
Vapor deposition rate of n and Al: 0.5 people/sec, substrate temperature: 2
Mn and Al at 00°C.

A total of 1000 layers were deposited in alternating order of Al. In this example, the deposition time of Mn and Al was increased to 40 seconds.

Furthermore, the substrate heating temperature was chosen to be as low as 200°C.

In this example, since the evaporation time is long, the film thickness of each layer is large and the mutual diffusion of Mn and Al during evaporation can cause
There is a region where the two do not mix. As a result, the Mn content ratio changes from 0 to 100 at%, and the thickness of the region where the Mn content ratio changes becomes 15.

Therefore, the rate of change in the Mn content ratio is 100 (at%)/15 [person] = 6.7 (at%/person), which is a large rate of change.The results of measuring the magnetic properties of this film 11 are as follows. , a large anisotropic magnetic field of 60,000 e was confirmed.

Further, the spontaneous magnetization of the film 11 was 100 emu/cc. Although this value is smaller than the values in Examples 1 and 2, the Mn content ratio in the films in Examples 1 and 2 is in the range of 45-65 at%, whereas in the film in this example, This is because there is a region of values outside this range. A region of the film in which the Mn content ratio is in the range of 45 to 65 at % is in the phase, and a region in which the Mn content ratio is outside this range is in the ε phase. As is clear from FIG. 5(b), these phases have a layered structure, and each layer is composed of the same phase. The τ phase is ferromagnetic and its spontaneous magnetization is 4
50 emu/cc, but since the ε phase is not ferromagnetic, the spontaneous magnetization is zero. The spontaneous magnetization of the entire film is the average value of the spontaneous magnetizations of the ferromagnetic phase layer and the non-ferromagnetic phase layer.

In the film of this example, the thickness of the τ phase region and the thickness of the ε phase region are 1:3, so the average value of spontaneous magnetization is 45
0X1/(1+3)=112 emu/cc, which roughly matches the above 100 emu/cc.

Embodiment 4 In this embodiment, an electron beam evaporation apparatus shown in FIG. 6 is used. Mn and Al are respectively put into two crucibles 20 in the electron gun heating device 7, and the positions of the crucibles are changed to deposit Mn and Al on the glass substrate 12 alternately in the order of Mn and Afl. The deposition rate is 5 per second in terms of film thickness.
angstrom, and the two crucible positions were switched every 10 seconds.

The substrate temperature was 250° C., and a total of 1000 layers were laminated.

In this example, since the evaporation rate is high, the film thickness of each layer is large, and as in Example 3, there is a region where Mn and Afl are not mixed due to mutual diffusion of Mn and Al during evaporation.

Example 5 In this example, a sputtering apparatus shown in FIG. 7 is used. This device is mounted on the target holder 9.
Mn particles and AΩ particles are simultaneously ejected from two targets 8 of n and Al by sputtering.
The stage 4 facing the surface of the substrate 12 is rotated to deposit Mn and Al alternately in the order of Mn and Al onto the substrate 12 held on the stage. The rotational speed of stage 4 and sputtering conditions were adjusted so that the amount of Mn and Al deposited was both 5 angstroms in terms of film thickness. In this example, the substrate temperature was 250°C, 1000 layers were laminated, and a film with the same structure as sample N001 of Example 1 was obtained, and the values of spontaneous magnetization and anisotropic magnetic field were also 450°.
A value equivalent to mu/cc, 14000e was obtained.

Note that the layer thickness can be varied in various ways by changing the rotation speed of the stage 4 of the sputtering device.

[Effects of the Invention] According to the present invention, reduction in spontaneous magnetization can be avoided even when the permanent magnet material M n -Al gold alloy is made into a thin film.
Furthermore, since magnetic anisotropy can be generated, application to various magnetic devices becomes possible.

[Brief explanation of the drawing]

FIG. 1(a) is a cross-sectional view of the present invention, FIG. 1(b) and FIG. 1(c) are diagrams showing the composition distribution of the present invention, FIG. 2 is a schematic diagram of an electron beam evaporation apparatus, and FIG. Figure (a) is a cross-sectional view of Example 1 of the present invention, Figure 3 (b) is a diagram showing the composition distribution of Example 1, Figure 4 (a) is a cross-sectional view of Example 2 of the present invention, and Figure 4 (a) is a cross-sectional view of Example 2 of the present invention. 4
Figure (b) shows the composition distribution of Example 2, Figure 5 (a)
is a sectional view of Example 3 of the present invention, and FIG. 5(b) is Example 3.
FIG. 6 is a schematic diagram of an electron beam evaporation device, FIG. 7 is a schematic diagram of a sputtering device, and FIG. 8 is a diagram showing the composition distribution of M n -A Q ferromagnetic thin films produced in Examples 1 to 3. FIG. 3 is a diagram showing film forming conditions, distribution of Mn content ratio, and magnetic properties. 1...Electron gun heating device, 2...Shutter, 3...
Substrate, 4... Stage, 5... Vacuum chamber, 6... Exhaust device, 7... Triple electron gun heating device, 8... Target, 9... Target holder, 10... Aperture , 11... Thin film, 12... Substrate, 2o... Crucible. Agent Patent Attorney Masaru Koyo? ('i' 茅/11 (C)
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Claims (12)

[Claims] 1. The Mn content ratio in the Mn-Al film is substantially constant in the plane direction of the film, and varies in the film thickness direction, and the Mn content ratio is 45 in at least a part of the film thickness direction. A Mn--Al ferromagnetic thin film characterized in that it is within a range of -65 at% and fluctuates. 2. The Mn--Al ferromagnetic thin film according to claim 1, wherein the maximum value of the Mn content ratio is 100 at% and the minimum value is 0 at%. 3. The quantitative ratio of Mn is 45-6 throughout the film.
The Mn--Al ferromagnetic thin film according to claim 1, wherein the Mn--Al ferromagnetic thin film is in the range of 5 at%. 4. 4. The Mn--Al ferromagnetic thin film according to claim 1, wherein the Mn content ratio varies periodically in the film thickness direction. 5. 4. The Mn--Al ferromagnetic thin film according to claim 1, wherein the Mn content ratio varies randomly in the film thickness direction. 6. The above Mn-Al film is a {10
4. The Mn--Al ferromagnetic thin film according to claim 1, wherein the Mn--Al ferromagnetic thin film is formed on a 0} plane. 7. 7. The Mn--Al ferromagnetic thin film according to claim 6, wherein said NaCl type single crystal is a MgO single crystal. 8. The Mn-Al ferromagnetic thin film according to claim 1 is formed by alternately depositing Mn and Al on a substrate heated within a range of 200 to 350° C. in a vacuum. A method for producing an Al ferromagnetic thin film. 9. 9. The method of manufacturing a ferromagnetic thin film according to claim 8, wherein said deposition is performed in the order of Mn and Al. 10. 10. The method of manufacturing a Mn--Al ferromagnetic thin film according to claim 9, wherein the substrate is made of NaCl type single crystal, and the adhered surface is a {100} plane. 11. 11. The method of manufacturing a Mn--Al ferromagnetic thin film according to claim 10, wherein the NaCl type single crystal is a MgO single crystal. 12. The Mn according to claim 8, wherein the deposition is performed by a vacuum evaporation method.
- A method for producing an Al ferromagnetic thin film.