JPH04127508A - Mn-al ferromagnetic thin film and manufacture thereof - Google Patents

Abstract

PURPOSE:To make it possible to conduct spontaneous magnetization equal to or higher than a alloy bulk, and to reduce the irregularity of characteristics by a method wherein, after an Mn-Al thin film has been formed on the surface (100) of an MgO single crystal substrate at 0 to 350 deg.C, and a heat treatment is conducted at 200 to 500 deg.C which is higher than the temperature of the substrate when it is formed. CONSTITUTION:Two electron beam heating devices 1 are placed in a vacuum vessel 6, Mn is put in one crucible 4 as the source of vapor deposition, Al is put in other crucible 4, both of them are evaporated simultaneously by heating, and Mn-Al film, in which the quantitative ratio of Mn in the film varies in film thickness direction, is formed by controlling the opening and closing of two shutters 2. Using an MgO single crystal face (100) as a substrate, a deposition operation is conducted by changing the quantitative ratio of Mn in the order of Mn surplus and Al surplus, and the substrate temperature is set in the range of to 350 deg.C. After deposition, a heat treatment is conducted at the temperature higher than the substrate temperature when a deposition operation is conducted, and an MnAl thin film, having the spontaneous magnetization larger than 450emu/cc, can be obtained.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an alloy thin film of manganese and aluminum,
6 concerning a film suitable for stably obtaining large spontaneous magnetization and magnetic anisotropy equal to or greater than that of a bulk alloy and its manufacturing method

[Conventional technology]

It is known that an alloy of manganese (Mn) and aluminum (Al) becomes a ferromagnetic material when it has a certain crystal structure, and its bulk crystal is used in permanent magnets and the like. In recent years, attempts have been made to make this material thinner. As an example, JP-A-1-315108 describes an M n -A 1 ferromagnetic thin film in which the Mn content ratio varies in the film thickness direction.

[Problem that the invention sought to solve]

In the above-mentioned conventional technology, the Mn content ratio is varied in the film thickness direction to obtain a spontaneous magnetization of 450 emu/cc, which is equivalent to that of a bulk alloy. However, when a large number of films are repeatedly produced, there is a problem in that the magnetic properties vary widely. The purpose of the present invention is to reduce the variation in the magnetic properties of the M n -A I thin film, and to reduce the variation in the magnetic properties of the M n -A I thin film, and to
The objective is to obtain an n-A I thin film.

[Means for Solving the Problems 1] The object of the present invention is to form a Mn-Al thin film on the (100) plane of an MgO single crystal substrate in a temperature range of 0 to 350°C, and then Higher and 200-500℃
This can be achieved by heat treatment at a temperature in the range of . The Mn--Al thin film produced by this method exhibits spontaneous magnetization equal to or higher than that of the bulk alloy, and has small variations in properties. [Function] In the process of obtaining the above-mentioned Mn content ratio variable film, various thin films were repeatedly produced. When the magnetic properties of these thin films were measured, variations were noticeable. As a result of examining the causes of this, it was found that the following three factors were the main causes. First, many lattice defects are introduced into the film. Because lattice defects deteriorate magnetic properties. Differences in the amount of lattice defects introduced cause variations in magnetic properties. Second, there are many restrictions on film formation conditions. The above-mentioned Mn content ratio variable film has many restrictions on the film forming conditions, such as the substrate temperature during film formation being limited to 200 to 350°C and the variation range of the Mn content ratio being limited to 45 to 65 at%. Therefore, film formation involves complications such as control of substrate temperature and Mn content ratio, and film formation cannot always be performed under desired conditions, resulting in variations in magnetic properties. Thirdly, because the time for which the film is maintained at high temperature near the substrate and near the surface is maintained at a high temperature for a significantly different time, differences occur in the magnetic properties of these parts, making it impossible to obtain good magnetic properties over the entire film. This is especially noticeable when film formation is carried out over a long period of time.In order to eliminate the cause of this phenomenon, we attempted heat treatment after film formation, and as a result, the following effects were observed. The substrate temperature was set at 200 to 350°C, and the Mn content ratio variation range was set at 4.
(Zoo
) The film fabricated on the surface has a spontaneous magnetization of 300 to 450e■
The spontaneous magnetization varied in the range of u/cc, but by applying heat treatment to these, the spontaneous magnetization increased slightly, and it was 420 to 48
It fell within the range of 0 ewu/cc. In other words, heat treatment can reduce the variation in spontaneous magnetization, and conventionally only a maximum spontaneous magnetization of 450 emu/cc could be obtained with an Mn-Al thin film.
Spontaneous magnetization larger than cc was obtained. These effects are thought to be due to the partial elimination of lattice defects in the film. In addition, films fabricated on the (100) plane of an MgO single crystal substrate at a substrate temperature of 200°C or lower did not exhibit ferromagnetism, but these films could also be treated by heat treatment.
A spontaneous magnetization of 480 emu/cc was obtained. Regarding variations in the Mn content ratio, it is not limited to the range of 45 to 65 at%, and even if the film is prepared in the range of 0 to 100 at% or constant, it can be changed to 480 en + u by heat treatment.
A spontaneous magnetization of /cc was obtained. That is, in order to obtain spontaneous magnetization equivalent to or higher than that of the bulk alloy, it is not necessary to limit the substrate temperature during film formation to 200 to 350° C. and the Mn content ratio variation range to 45 to 65%. Therefore, since strict control of conditions during film formation is not required, film formation is easy, and variations in magnetic properties due to many restrictions on film formation conditions can be prevented. Furthermore, as mentioned above, even if the substrate temperature is set to 200°C or less, it is possible to fabricate a M n -Al thin film that exhibits spontaneous magnetization equal to or higher than that of a bulk alloy, which makes it possible to reduce the variation in spontaneous magnetization within the film. It is also effective. In order to obtain a spontaneous magnetization equivalent to that of a bulk alloy in a conventional variable Mn ratio film, it is necessary to use an MgO single crystal (1
It was preferable to use the 00) plane. Therefore, in the experiments leading up to the present invention, we have mainly studied films deposited on the (100) plane of MgO single crystal substrates. Similar studies were conducted on films deposited on other substrates, such as glass, NaCl, LiF, NaF, etc., but for any of the substrates, what effect did it have when using an MgO single crystal substrate? I couldn't get it. This is thought to be because a structure exhibiting ferromagnetism is likely to be formed on the (100) plane of the MgO single crystal. Furthermore, when using an MgO single crystal, it is preferable to form an Mn layer or an excessive Mn layer directly on the substrate. This is thought to be because a structure exhibiting ferromagnetism is likely to be formed. [Example 1 Example 1 In this example, an electron beam evaporation apparatus shown in FIG. 3 was used. Electron beam heating equipment in vacuum chamber 6! Two crucibles 1 were placed, and manganese (Mn) was placed in one crucible 4 and aluminum (Al) was placed in the other crucible 4 as materials for the vapor deposition source 3, and heated to evaporate both at the same time. The degree of vacuum during vapor deposition is lXl
It is desirable that the value is 0-'Torr or less, and in this example, lXl0
"-gT.rr. By controlling the opening and closing of the two shutters 2, the Mn content ratio in the film varies in the film thickness direction.
An n-Al film was prepared. The structure of the produced thin film is as shown in FIG. 4, in which layers with a large Mn content and layers with a large Al content are alternately laminated. The quantity ratio fluctuation range and fluctuation period of Mr+ are as follows:
Same as the above conventional technology. That is, the variation range of the Mn content ratio is 45 to 65 at%,
The fluctuation period was set to 20 Å or less. The (100) plane of MgO single crystal was used as the substrate, and Mg was added in the order of excess Mn and excess Al.
The deposition was carried out by changing the ratio of n to a film thickness of about 4,000. The substrate temperature is also 20, the same as in the conventional technology.
The temperature was set within the range of 0 to 350°C. When we measured the spontaneous magnetization of the M n -A I thin films produced in this way, some showed a spontaneous magnetization of 450 e*u/cc, which is equivalent to that of bulk alloys, as in the conventional technology, but many As a result, the spontaneous magnetization is 3
It was found that it varies in the range of 00 to 450e cabinet u/cc. Therefore, we attempted heat treatment of these films. Heat treatment is lXl
This was carried out by maintaining the temperature at 350°C for 1 to 8 hours under a vacuum degree of 0-' Torr. The spontaneous magnetization of the film after heat treatment was also measured. FIG. 1 shows the above measurement results. The vertical lines in the figure represent the range of variation in spontaneous magnetization, and the circles represent the average value. After heat treatment for 1 to 2 hours, the spontaneous magnetization increases slightly, and the range of variation becomes smaller. This is considered to be because defects in the film were partially eliminated. This effect is 1
Spontaneous magnetization appears after heat treatment for about 1 hour, and no increase in spontaneous magnetization is observed even if heat treatment is continued, and when heat treatment is performed for a long time of 4 hours or more, spontaneous magnetization rapidly decreases. This is thought to be because the ferromagnetic structure was destroyed by diffusion. Next, heat treatment was performed at a temperature of 100 to 600° C. for 1 hour, and the results are shown in FIG. This result shows that the heat treatment is 200~5
It is effective when carried out at a temperature of 00°C, especially at a temperature of 300°C to
This shows that a temperature of 400°C is good. Example 2 In this example, the same apparatus as in Example 1 was used to produce a film having the same structure. The variation range and variation cycle of the Mn ratio were also the same as in Example 1. However, the substrate temperature was set at a temperature of 200° C. or lower, at which conventionally almost no spontaneous magnetization could be obtained. However, although it was not possible to set a temperature lower than 0° C. due to the structure of the film forming apparatus, it is considered to be undesirable from a practical standpoint because cooling would be complicated. Spontaneous magnetization was measured for the films produced under these conditions, and none of the films showed almost any ferromagnetism. These films were subjected to a vacuum of 1X10-7 Torr at 35
When heat treated at 0 DEG C. for 2 hours, all films exhibited spontaneous magnetization of 380 to 480 eU/cc, as shown in Table 1. From the above, the present invention is effective in reducing restrictions on film formation conditions, particularly on substrate heating temperature during film formation. With this, for example, film formation can be performed without heating the substrate. Table 1 Also, when forming a film under conventional substrate temperature conditions of 200 to 350°C, it takes a long time to form the film, such as by reducing the film thickness to 4,000 to 8,000 people and the deposition rate to 1 person/sec or less. When necessary, the properties of the initially deposited layer change due to the effects of substrate heating during film formation, possibly resulting in property deterioration. In other words, the thin film has a small spontaneous magnetization near the substrate and a large spontaneous magnetization near the surface. However, according to the present invention, since the film can be formed without heating the substrate, deterioration of the properties during film formation can be avoided, and even if there is local fluctuation in the magnetic properties, the magnetic properties are the same near the substrate and near the surface. Such,
A thin film with uniform magnetic properties over a wider range can be obtained. Example 3 In this example, Mn and Al are deposited simultaneously by using the same apparatus as in Example 1 and opening the two shutters 2 at the same time. The substrate is MgO single crystal (100)
After forming a Mn layer with a thickness of 100 layers on the substrate using a surface, Mn and Al were simultaneously vapor-deposited. Vapor deposition has a film thickness of 500
I went until there were 0 people left. After measuring the spontaneous magnetization of these films, the films were kept at 350° C. for 1 hour under a vacuum of 1X10-' Torr as a heat treatment, and the spontaneous magnetization was measured again. The above results are summarized in Table 2. Although almost no spontaneous magnetization was detected in any of the films immediately after deposition, the heat-treated films were able to obtain almost the same spontaneous magnetization as the bulk alloy. From the above, according to the present invention, by simply depositing Mn and Al at the same time without changing the Mn content ratio in the film thickness direction, the 4-50 emu/
cc spontaneous magnetization is obtained. That is, complicated shutter control during film formation is not required, and the associated waste of time and raw material consumption can be reduced. Example 4 In this example, film formation was performed using a DC sputtering apparatus. Using two targets, Mn and Al, A
r pressure 2 mTorr, input power density 0, 5 W/c
The deposition rate was 4 people/sec. The (100) plane of MgO single crystal was used as the substrate, and the film thickness was 5000 people. Mn and Al were deposited simultaneously. Examples 1 and 2 are the case where Mn and Al are deposited alternately and the case where Mn and Al are deposited alternately, respectively.
The results were almost the same as in the case of vacuum evaporation shown in . That is, even in a sample prepared under film-forming conditions in which spontaneous magnetization could hardly be obtained, spontaneous magnetization almost equivalent to that of the bulk alloy was obtained by applying an appropriate heat treatment. From the above, the present invention can also be applied to a case where a film is formed by sputtering. [Effects of the Invention] According to the present invention, the alloy has a spontaneous magnetization equivalent to that of a bulk alloy.
Since the M n -A 1 ferromagnetic thin film can be easily produced, it can be applied to various magnetic devices.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between spontaneous magnetization and heat treatment time of the M n -Al ferromagnetic thin film produced in Example 1 of the present invention, FIG. 2 is a diagram also showing the relationship between spontaneous magnetization and heat treatment humidity, and FIG. FIG. 3 is a schematic diagram of an electron beam evaporation apparatus, and FIG. 4 is a cross-sectional view of the M n -Al ferromagnetic thin film produced in Example 1 of the present invention. Explanation of symbols 1...Electron beam heating device, 2...Shutter, 3...
Vapor deposition source, 4... Crucible, 5... Stage, 6...
Vacuum chamber, 7... Exhaust device, 8... Thin film, 9... Substrate

Claims (2)

[Claims] 1. An Mn-Al ferromagnetic thin film formed on the (100) plane of an MgO single crystal substrate and characterized by having spontaneous magnetization greater than 450 emu/cc. 2. First, Mn is deposited on the (100) plane of an MgO single crystal substrate maintained at a temperature of 0 to 350°C, and then Mn and A are deposited.
1. A method for producing a Mn--Al ferromagnetic thin film, the method comprising: depositing Mn--Al ferromagnetic thin film, and after deposition, heat-treating at a temperature higher than the substrate temperature at the time of deposition and in the range of 200 to 500C. 3. Above M
3. The Mn-Al according to claim 2, wherein the deposition of n and Al is performed alternately with deposition of Mn and deposition of Al.
A method for producing a ferromagnetic thin film.