JP2735276B2 - Mn-Al ferromagnetic thin film and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a manganese-aluminum alloy thin film, and more particularly to a film suitable for generating large spontaneous magnetization and magnetic anisotropy equivalent to a bulk alloy.

[Prior art]

An alloy of manganese (Mn) and aluminum (Al) is known to be a ferromagnetic material in a certain crystal structure.
The bulk crystal has been applied to permanent magnets and the like. recent years,
Attempts have been made to make this material thinner. One example is the Journal of Applied Physics, 61
(1987) p. 4281 to p. 4283 (J. Appil. Phys. 61 (1
987), pp.4281-4283), the ratio of Mn to Al is constant in the Mn-Al alloy film formed by the sputtering method.

[Problems to be solved by the invention]

In the above prior art, the spontaneous magnetization of the obtained film is 120 emu / cc at the maximum even if the film forming conditions are variously changed.
However, there is a problem that the thickness is only about 1/4 of that of the bulk alloy. The reason for this is that even if the ratio of Mn and Al is constant,
This is because a non-magnetic structure (ε phase) is included together with a structure that generates ferromagnetism (τ phase). A first object of the present invention is to obtain a Mn-Al ferromagnetic thin film having a τ phase throughout the film and having spontaneous magnetization equivalent to that of a bulk alloy. In magnetic devices, magnetic anisotropy is also an important characteristic. For example, in perpendicular magnetic recording, anisotropy in the direction perpendicular to the film is indispensable. A second object of the present invention is to generate magnetic anisotropy that cannot be obtained by the above-mentioned conventional technology.

[Means for Solving the Problems]

The first object of the present invention is to provide an Mn-Al film in which the Mn content ratio is approximately constant in the plane direction of the film and fluctuates in the film thickness direction within the range of 45 to 65 at%. -It can be achieved by preparing an Al film. The second object of the present invention is that the quantitative ratio of Mn in the Mn-Al film is substantially constant in the plane direction of the film, fluctuates in the film thickness direction, and at least in the film thickness direction of the film. Partly above
This can be achieved by forming a Mn-Al film in which the Mn content ratio is in the range of 45 to 65 at% and fluctuates.

[Action]

The background to achieve the first object of the present invention is as follows. In the above prior art, the spontaneous magnetization is small due to the fact that the τ phase of the ferromagnetic structure is in a metastable state. Therefore, a condition in which the τ phase is generated more stably than the ε phase was sought. As one of them, various Mn-Al alloys having different spontaneous magnetizations were cut, and the composition of the cross section was examined microscopically. as a result,
It was found that those having a large spontaneous magnetization consisted of only the τ phase, and those having a small spontaneous magnetization contained both the τ phase and the ε phase. When the composition of the region where the τ phase exists was examined, the quantitative 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 content ratio of Mn was 45 to 65 at.
It was expected that a large spontaneous magnetization would be obtained if the τ phase was formed preferentially by artificially changing the composition in the range of%. That is, it was considered that if Mn and Al were alternately stacked on the substrate by a vacuum deposition method or the like and these two Mn and Al elements were mutually diffused, the Mn quantitative ratio would fluctuate in the thickness direction of the film. Based on this idea, various thin films having different variations in the Mn fraction ratio were prepared using the deposition rate, deposition time, and substrate heating temperature as parameters. The structure of the fabricated thin film is as shown in FIG.
It has a structure in which films with a large amount of Mn and films with a large amount of Al are alternately stacked. The distribution in the thickness direction of the Mn fraction ratio of this thin film is the first.
It is as shown in FIG. FIG. 1 (b) shows the variation in the Mn content ratio when a film with a large Mn content (excess) and a film with a large Al content (excess) are stacked. Al content ratio is 100a
It is obtained by subtracting the ratio of Mn from t%. The range of variation of the discount of Mn is in the range of 0 to 100. The regions a and b are regions in which Mn and Al are not mixed and pure Mn and Al remain even when mutual diffusion of Mn and Al occurs. The area of c and d is Mn
In this region, Al and Al have been interdiffused, and the ratio of Mn is gradually changing. If the layer thickness is small, the interdiffusion between Mn and Al
The entire region of the Mn layer and the Al layer is covered, and as a result, the regions a and b do not exist, but only the composition fluctuation regions c and d. FIG. 1 (c) shows the distribution of the Mn ratio in the film thickness direction in this case. The variation range of the Mn content ratio is x ₂ from x _1. FIG. 8 shows the conditions for forming a thin film, Mn
The distribution of the ratio and the magnetic properties such as spontaneous magnetization are shown. The spontaneous magnetization of the thin film of Sample No. 1-11 is 450 emu / 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 has achieved the first object of the present invention has been realized. At this time, the smallest value of the minimum value x ₁ of the Mn fraction ratio is:
Sample No. 3 is 45 at%, and the largest value among the maximum values x ₂ is 65 at% of Sample Nos. 6 and 7. Therefore, the variation range of the Mn fraction ratio is 45-65 at%. In addition, the number of laminations
A spontaneous magnetization of 450 emu / cc can be obtained even when changed in the range of 00, and 450 emu / cc even when the period is changed in the range of 8 ° to 20 °.
Is obtained. Therefore, it can be seen that spontaneous magnetization equal to that of the bulk alloy can be obtained even when films having various structures with different numbers of layers and periods are manufactured. In addition, the sample
In the structure of No. 11, the minimum value and the maximum value of the period and the Mn fraction ratio have random values in the film thickness direction. The spontaneous magnetization of the sample having such a structure is 450 emu / cc as in the case of the sample in which the above three parameters are constant. Therefore, if the Mn content ratio is in the range of 45-65 at%, spontaneous magnetization equal to that of the bulk alloy can be obtained even for films having different numbers of laminations, periods, and minimum and maximum values of the Mn content ratio. It can be seen that it can be obtained. In sample No. 12, the spontaneous magnetization of the film was 100 emu /
Smaller than cc and bulk alloys. This is because the Mn
Is considered to be in the range of 0 to 100 at%. The fractional ratio of Mn, which is a part of this film, is 45
In the region of ~ 65 at%, a τ phase is generated, and the spontaneous magnetization has the same value as that of the bulk alloy, that is, 450 emu / cc. , Where the value of the spontaneous magnetization is zero. The spontaneous magnetization of the film is the average 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 that the average value of the spontaneous magnetization is 450 × 1 / (1 + 3) = 1.
Calculated as 12 emu / cc. This value approximately matches the above-mentioned 100 emu / cc. From this, it is also necessary to set the Mn ratio to 45 to 65.
It is understood that the condition of at% is a condition for generating ferromagnetism. Next, the operation of the means for achieving the second object of the present invention will be described. As can be seen from FIG. 8, anisotropic magnetic fields were generated in all the samples, and it was found that thin films that achieved the second object of the present invention were realized. In particular, in Sample No. 12, the value of the anisotropic magnetic field is as large as 6000 Oe. In this sample, the value of spontaneous magnetization is as small as 100 emu / cc. However, it can be used for a magneto-optical recording medium or the like. The feature of the two samples is that the rate of change of the Mn fraction ratio is large. This is because the rate of change of the Mn fraction ratio and the anisotropic magnetic field are
It can be seen from the proportional relationship in all the samples in FIG. As one method for producing the Mn-Al ferromagnetic thin film of the present invention, Mn is formed on a substrate under heating of the substrate at 200 to 350 ° C. in vacuum.
There is a method of alternately depositing Al. As a substrate, ｛10
NaCl-type single crystal of 0 plane is preferable, and MgO of {100} plane is particularly preferable.
Single crystals are preferred. In general, when a film is formed at a low temperature of about room temperature, crystal disorder is large and good characteristics cannot be obtained. The ferromagnetic thin film has effects such as a decrease in spontaneous magnetization, an anisotropic magnetic field, and the like. On the other hand, if the temperature during the film formation is too high, adverse effects such as a change in the film composition occur. For example, when depositing various elements having different saturated vapor pressures, if the substrate temperature is too high, a desired composition cannot be obtained because elements having a high saturated vapor pressure re-evaporate from the substrate during deposition. In the Mn-Al thin film of the present invention, as is clear from the results in FIG. 8, good results have been obtained by heating the substrate to 200 ° C. to 350 ° C. to form the film. In the examples, Mn was applied first. When Al is first deposited, the spontaneous magnetization and the anisotropic magnetic field are slightly inferior to those of the example, but it is confirmed that they are superior to the conventional Mn-Al thin film.

【Example】

Embodiment 1 FIGS. 2 and 3 (a) and (b) show Embodiment 1 of the present invention.
This will be described below. In this embodiment, the electron beam evaporation apparatus shown in FIG. 2 was used. Two electron gun heaters 1 are placed in a vacuum chamber 5, and manganese (Mn) and aluminum (Al) are put into crucibles 20 of the respective electron gun heaters and heated, and are heated under a vacuum of 1 × 10 ^-9 Torr. To deposit both at the same time. By alternately opening and closing the two shutters 2 in this state, Mn and Al are alternately deposited on the glass substrate 12 attached to the stage 4 in the order of Mn and Al. In Sample 1, the deposition speed was 0.5 ° per second, and the shutter was opened and closed every 10 seconds. Therefore, the film thickness 5
Å A considerable layer is deposited. Keep substrate temperature at 250 ° C for 100
Zero layers were laminated. FIGS. 3 (a) and 3 (b) show the cross-sectional structure of the film of Sample 1 and the composition change in the film thickness direction, respectively. Deposition layer thickness is 5mm
In this case, the interdiffusion of Mn and Al extends over the entire region of the Mn layer and the Al layer, and as a result, only a region having a thickness of 5 ° and a composition change is present. Since the maximum value of the Mn fraction ratio is 54 at% and the minimum value is 46 at% in this region, the variation rate of the Mn fraction ratio is (54 [at
%]-46 [at%]) / 5 [Å] = 1.6 [at% / Å]. As a result of measuring the magnetic properties of this film, the spontaneous magnetization of the film was 450 emu / cc, which is equivalent to that of the bulk alloy, and the anisotropic magnetic field was 1400 Oe. Furthermore, various films were formed under different film forming conditions. The changed film formation conditions are the substrate temperature at the time of fabrication, the shutter open time of Mn and Al, the deposition rate R, and the number of layers N. FIG. 8 shows the film forming conditions of the manufactured sample Nos. 2 to 10. FIG. 8 also shows the distribution of the Mn composition and the two vapor characteristics of the anisotropic magnetic field and the spontaneous magnetization in these samples. Substrate is sample No.6-8
Is a {100} plane MgO single crystal, and the other samples are glass. Mn and Al are deposited on these two kinds of substrates at a substrate temperature of 200 ° C. to 350 ° C.
They were applied alternately in the order of l. The deposition rate is 0.5Å / sec and 1
Å / sec, and the shutter release time is in the range of 8 to 12 seconds. The distribution of the Mn fraction ratio in the film thickness direction is determined by the substrate temperature, the shutter open time, and the deposition rate. In Sample Nos. 2 to 10, the mutual diffusion of Mn and Al extends over the entire region of the Mn layer and the Al layer. As a result, only the region where the composition fluctuates exists. The width of the region where the composition fluctuated, that is, c in FIG.
And d are in the range of 4-6 ° for these samples. Further, the Mn fraction ratio was in the range of 45 to 65 at% for all samples. The spontaneous magnetization of the films of Sample Nos. 2 to 10 is
450 emu / cc, which was equal to that of the bulk alloy. As apparent 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 when the number of layers was changed. The anisotropic magnetic field of Sample Nos. 2 to 10 was 30 as shown in FIG.
It ranges from 0 Oe to 2200 Oe. This is the M shown in the figure.
It is proportional to the n-quantity change rate. Therefore, an improvement in the anisotropic magnetic field can be expected by selecting film forming conditions that increase the Mn content change rate. Embodiment 2 FIGS. 4 (a) and 4 (b) show Embodiment 2 of the present invention.
This will be described below. Sample No. 11 shown in this example was manufactured using the electron beam evaporation apparatus shown in FIG. On the glass substrate 12, the deposition rate of Mn and Al is 0.5n / sec, and the substrate temperature is 250 ° C.
Mn and Al were alternately deposited in the order of Mn and Al for a total of 1000 layers. In this embodiment, the deposition time of Mn and Al was changed at random.
For this reason, the shutter opening time was changed in the range of 10 to 12 seconds for Mn, and was changed in the range of 8 to 10 seconds for Al. As a result, as shown in FIG.
A ferromagnetic film in which Al excess layers are alternately stacked is manufactured. At this time, the thicknesses of the respective layers are not the same as in the first embodiment. Further, as shown in FIG. 4 (b), the maximum value and the minimum value of the Mn fraction ratio are not constant, unlike the case of the first embodiment. The maximum value of the Mn fraction 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 equivalent to the value of the bulk alloy. The anisotropic magnetic field was 1000 Oe. Embodiment 3 Embodiment 3 performed to make the magnetic anisotropy appear will be described with reference to FIGS. 5 (a) and 5 (b). Since magnetic anisotropy is symmetrically related, it increases as the composition change increases. From this viewpoint, the film formation conditions were selected for sample No. 12, and the Mn ratio was 0 at% as shown in FIG.
From 100% to 100at%. FIG. 5 (a) shows a superlattice structure film 11 composed of Mn-excess and Al-excess layers produced under this condition, and 1000 layers each having a thickness of 20 angstroms [Å] are laminated on a glass substrate 12. . Hereinafter, the manufacturing method will be described. As the vapor deposition device, the electron beam vapor deposition device shown in FIG. 2 was used. On the glass substrate 12, Mn
And Al at a deposition rate of 0.5Å / sec and a substrate temperature of 200 ° C
Were deposited alternately in the order of Mn and Al for a total of 1000 layers. In this example, the deposition time of Mn and Al was increased to 40 seconds. Also,
The substrate heating temperature was selected as low as 200 ° C. In this embodiment, since the deposition time is long, the thickness of each layer is large, and there is a region where Mn and Al do not mix even when Mn and Al are interdiffused during the deposition. As a result, the Mn fraction ratio is 0 to 100a.
tÅ, the thickness of the region where the Mn fraction ratio changed was 15 mm
Becomes Therefore, the change rate of the Mn fraction ratio is 100 [at%] / 15 [Å] = 6.7 [at% / Å], and a large change rate can be obtained. As a result of measuring the magnetic properties of the film 11, a large anisotropic magnetic field of 6000 Oe was confirmed. The spontaneous magnetization of the film 11 was 100 emu / cc. This value is smaller than the values in Examples 1 and 2. This means that the Mn content ratio in the films in Examples 1 and 2 was 45-65.
This is because the film in the present embodiment has a region with a value out of the range, whereas the film is in the range of at%. The region of the film where the ratio of Mn is in the range of 45-65 at% is the τ phase, and the region where the value deviates from this range is the ε phase. These phases have a layered structure as is apparent from FIG. 5 (b), and one layer is composed of the same phase.
The τ phase is ferromagnetic and its spontaneous magnetization is 450 emu / cc.
Since the phase is not photomagnetic, 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 layer. In the film of this example, the thickness of the τ-phase region and the thickness of the ε-phase region were 1: 3, so the average value of the spontaneous magnetization was 450 ×
1 / (1 + 3) = 112 emu / cc, which is almost the same as 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 put into the two crucibles 20 in the electron gun heating device 7, respectively, and the positions of the crucibles are switched so that Mn and Al are alternately deposited on the glass substrate 12 in the order of Mn and Al. The deposition rate was 5 Å per second in terms of film thickness, 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 embodiment, since the deposition rate is high, the thickness of each layer is large, and there is a region where Mn and Al do not mix even by mutual diffusion of Mn and Al during the deposition as in the third embodiment. Embodiment 5 In this embodiment, a sputtering apparatus shown in FIG. 7 is used. This device was attached to the target holder 9
Sputtering from two targets 8 of Mn and Al
The Mn particles and the Al particles are simultaneously ejected, the stage 4 facing the surface of the target 8 is rotated, and Mn and Al are alternately deposited on the substrate 12 held on the stage in the order of Mn and Al. . The rotation speed of the stage 4 and the sputtering conditions were adjusted so that the deposition amounts of Mn and Al were both 5 Å in terms of film thickness. The substrate temperature was 250 ° C., and 1000 layers were stacked. In this example, a film having a structure equivalent to that of the sample No. 1 of Example 1 was obtained, and the values of the spontaneous magnetization and the anisotropic magnetic field were 450 emu / c.
c, values equivalent to 1400 Oe were obtained. The layer thickness can be variously changed by changing the rotation speed of the stage 4 of the sputtering apparatus.

【The invention's effect】

According to the present invention, it is possible to avoid a decrease in spontaneous magnetization even if the Mn-Al alloy as a permanent magnet material is thinned,
Since magnetic anisotropy can be generated, it can be applied to various magnetic devices.

[Brief description of the drawings]

1 (a) is a sectional view of the present invention, FIGS. 1 (b) and 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. FIG. 3A is a sectional view of Example 1 of the present invention, FIG. 3B is a diagram showing a composition distribution of Example 1, FIG. 4A is a sectional view of Example 2 of the present invention, FIG. 4
FIG. 5 (b) shows the composition distribution of Example 2, and FIG. 5 (a)
FIG. 5 is a sectional view of a third embodiment of the present invention, and FIG.
FIG. 6 is a schematic view of an electron beam evaporation apparatus, FIG. 7 is a schematic view of a sputtering apparatus, and FIG. 8 is a schematic view of the Mn-Al ferromagnetic thin film prepared in Examples 1 to 3. FIG. 3 is a diagram showing film conditions, distribution of Mn fraction ratio, and magnetic characteristics. DESCRIPTION OF SYMBOLS 1 ... Electron gun heating device, 2 ... Shutter, 3 ... Substrate, 4 ... Stage, 5 ... Vacuum tank, 6 ... Exhaust device, 7 ... Triple electron gun heating device, 8 ... Target , 9 ... target holder, 10 ... aperture, 11 ... thin film, 12 ... substrate, 20 ... crucible.

Claims (12)

(57) [Claims] An amount ratio of Mn in a Mn-Al film is substantially constant in a plane direction of the film, fluctuates in a film thickness direction, and at least a part of the film in the film thickness direction of the Mn-Al film. The Mn-Al ferromagnetic thin film, wherein the content ratio of the Mn-Al ferromagnetic thin film is in the range of 45-65 at% and fluctuates. 2. The Mn-Al ferromagnetic thin film according to claim 1, wherein the maximum value of the Mn fraction ratio is 100 at% and the minimum value is 0 at%. 3. The composition ratio of Mn is 45% over the entirety of the film.
The Mn-Al ferromagnetic thin film according to claim 1, wherein the thickness is in the range of -65at%. 4. The Mn-Al ferromagnetic thin film according to claim 1, wherein the Mn quantitative ratio fluctuates periodically in the film thickness direction. 5. The Mn-Al ferromagnetic thin film according to claim 1, wherein the Mn content ratio fluctuates randomly in the film thickness direction. 6. The Mn-Al film is a NaCl-type single crystal substrate of # 10
The Mn- according to claim 1, 2 or 3, which is formed on a 0 ° plane.
Al ferromagnetic thin film. 7. The Mn-Al ferromagnetic thin film according to claim 6, wherein the NaCl-type single crystal is a MgO single crystal. 8. An Mn-Al ferromagnetic thin film according to claim 1 formed by alternately depositing Mn and Al on a substrate heated in a temperature range of 200 to 350 ° C. in a vacuum. Feature
A method for producing a Mn-Al ferromagnetic thin film. 9. The method for producing a ferromagnetic thin film according to claim 8, wherein the deposition is performed in the order of Mn and Al. 10. The method for producing a Mn-Al ferromagnetic thin film according to claim 9, wherein said substrate is made of a NaCl-type single crystal, and said adherend surface is a {100} plane. 11. The method for producing a Mn-Al ferromagnetic thin film according to claim 10, wherein said NaCl-type single crystal is a MgO single crystal. 12. The method for producing a Mn-Al ferromagnetic thin film according to claim 8, wherein said deposition is performed by a vacuum deposition method.