JP7587795B2 - Tetragonal thin film structure - Google Patents

Description

The present invention relates to a tetragonal thin film structure having a tetragonal thin film on a supporting substrate, and is suitably applied to a tetragonal thin film having, for example, a thin film of FeNiN or an _L10 type FeNi ordered alloy having an _L10 type ordered structure.

FeNi (iron-nickel) ordered alloys with an L1 ₀ type ordered structure have high magnetic anisotropy and are expected to be used as magnet materials and magnetic device materials for magnetic recording, etc., without using any rare earths or precious metals. A thin film of L1 ₀ type FeNi ordered alloy can be formed on a support substrate of STO (strontium titanate (SrTiO ₃ )) by denitrifying an FeNiN thin film prepared by MBE (molecular beam epitaxy) in nitrogen plasma (see Non-Patent Document 1).

K. Ito et al., "Epitaxial L10-FeNi films with high degree of order and large uniaxial magnetic anisotropy fabricated by denitriding FeNiN films", Applied Physics Letters. 116, 242404(2020)

However, it was confirmed that when a thin FeNiN film is formed on a support substrate whose main surface has a (100) surface orientation using the manufacturing method disclosed in Non-Patent Document 1, two types of variants are created in which the c-axes of the FeNiN intersect at 90 degrees. This is because the crystal structure on the (100) surface has four-fold symmetry around the central axis, and the FeNiN grows so that the c-axis intersects each side of the cubic crystal structure, resulting in a multi-variant state. The dimensions of each variant in this case were up to 5 nm.

In a multivariant state where the crystal orientation axes are perpendicular to each other, the magnetic, electrical, and optical properties of the orientation direction with excellent properties and those of the orientation direction with poor properties are averaged, and there is a problem that the properties that would be obtained in a single variant state cannot be utilized. For example, the magnetocrystalline anisotropy constant Ku becomes an averaged value, and the magnetocrystalline anisotropy decreases.

Note that "variant" here refers to the crystal orientation that a tetragonal thin film has when it is formed on a supporting substrate; "single variant" means that the crystal orientation is in only one axial direction, while "multi-variant" means that the crystal orientation is in multiple axial directions. It is not necessary for the entire tetragonal thin film to be "single variant," but if it is "multi-variant" and the dimensions of each variant are small, there is no dominant variant, and the characteristics are averaged out, making it impossible to obtain good characteristics. For this reason, in order to obtain better characteristics, it is important to obtain large dimensions for the single variant.

In view of the above, the present invention aims to provide a tetragonal thin film structure with superior properties.

In order to achieve the above object, the tetragonal thin film structure according to claim 1 comprises a support substrate (10) having a crystal structure belonging to a cubic system, the support substrate having a main surface on which monolayer steps (11) are formed and which is oriented at a predetermined off angle with respect to the (100) plane, and an FeNi ordered alloy thin film (20) formed on the main surface of the support substrate, the thin film being made of an _L10 type FeNi ordered alloy and having a width corresponding to the monolayer steps, and in which slits (21) are formed. The support substrate has 6 or more monolayer steps per 1 μm in the off direction.

In this way, by forming an FeNi ordered alloy thin film on a support substrate whose main surface has an off-angle with respect to the (100) plane, the crystals of the FeNi ordered alloy thin film can be made to be single variant. This makes it possible to obtain a tetragonal thin film structure with superior properties.

The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and the specific components described in the embodiments described below.

1 is a cross-sectional view of a tetragonal thin film structure according to one embodiment of the present invention. 1B is a top view of a tetragonal thin film of the tetragonal thin film structure shown in FIG. 1A. FIG. 1A is a perspective view of the crystal structure of STO, FIG. 1B and FIG. 1C are views of STO(100) and STO with an off angle, respectively, as viewed from the normal direction of the main surface before the off angle is provided, FIG. 1D is a diagram showing a unit lattice of the crystal structure as viewed from the b-axis direction, and FIG. 1E is a view of the crystal structure as viewed from the normal direction of the main surface before the off angle is provided, when the Sr—O plane is the outermost surface, by dividing the crystal structure from FIG. 1C by the main surface before the off angle is provided. FIG. 2 is a cross-sectional view of a tetragonal thin film structure according to a comparative example. 3B is a top view of a tetragonal thin film of the tetragonal thin film structure shown in FIG. 3A. FIG. FIG. 2 is a schematic diagram showing the state of matching between STO(100) and FeNiN(100). 1 is a table summarizing the measurement conditions and measurement results for Comparative Examples 1 to 3 and Examples 1 and 2. 1 is an AFM (atomic force microscope) image of a main surface of Example 1. 1 is an AFM image of a main surface of Example 2. 4 is a TEM (transmission electron microscope) image of a cross section of the FeNi ordered alloy thin film of Example 2. 1 is a graph showing the relationship between the off angle and the coercive force Hc. 1 is a cross-sectional TEM image used to examine the variant size of an FeNi ordered alloy thin film. FIG. 9 is a diagram showing a result of TEM electron beam diffraction in a region A in FIG. 8 . 9B is a diagram showing the TEM electron beam diffraction results in region B in FIG. 8, with the same scale as FIG. 9A. FIG. 9B is a diagram showing the TEM electron beam diffraction results in region C in FIG. 8, with the same scale as FIG. 9A.

The following describes embodiments of the present invention with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other are denoted by the same reference numerals.

First Embodiment
A tetragonal thin film structure according to a first embodiment will be described with reference to Figures 1A and 1B. In Figures 1A and 1B, the arrows shown in the figures indicate the direction of the c-axis.

As shown in FIG. 1A, the tetragonal thin film structure of this embodiment is configured by forming an L1 ₀ type FeNi ordered alloy thin film 20 having an L1 ₀ type ordered structure on a support substrate 10 .

The support substrate 10 has a crystal structure belonging to a cubic crystal system, and the main surface on the side in contact with the FeNi ordered alloy thin film 20 is an off-substrate having a predetermined off-angle with respect to the (100) plane orientation, and the main surface has monoatomic layer steps 11 based on the off-angle. For example, an off-substrate having an off-angle in the [010] direction with respect to STO (100) can be used as the support substrate 10. By configuring the support substrate 10 as an off-substrate, the symmetry of the crystal structure on the main surface of the STO can be reduced, that is, it can be made to be no longer four-fold symmetric. Therefore, when growing a metal containing Fe, Ni, and N, which is a precursor when forming the FeNi ordered alloy thin film 20, such as FeNiN, the direction that matches with FeNiN can be made to be one direction. In other words, when growing FeNiN on the surface of STO(100), there are two directions of alignment, but by growing FeNiN on a main surface that has an off-angle with respect to STO(100), it is possible to make it easier to align in one of the directions. This suppresses multi-variant growth, and allows for single-variant growth between each monolayer step 11.

The (100) written after STO means that the plane orientation of STO is (100). In this embodiment, the main surface of the support substrate 10 has an off angle with respect to STO (100), which means that the main surface has an off angle with respect to the (100) plane orientation. In the following, the direction of the vector obtained by projecting the normal vector of the main surface of the support substrate 10 onto the (100) plane is referred to as the off direction.

As shown in (a) in FIG. 2, STO has a cubic crystal structure. Therefore, when the crystal structure of STO (100) is viewed from above, it becomes the structure shown in (b) in FIG. 2. In contrast, in the case of the support substrate 10 of this embodiment, since the main surface has an off-angle with respect to STO (100), when the STO constituting the support substrate 10 is viewed from the normal direction to the main surface, it becomes the structure shown in (c) in FIG. 2. In other words, as shown in (c) in FIG. 2, the atoms of each layer in the crystal of STO do not completely overlap. Here, for example, as shown in (d) in FIG. 2, if the crystal structure is divided by the main surface before the off-angle is applied and the Sr-O surface is the outermost surface, as shown in (e) in FIG. 2, a monoatomic layer step is formed when focusing on Sr, and in the case of STO (100) as shown in (b) in FIG. 2, the cubic crystal lattice constant is 0.3905 nm, but in the structure of (e) in FIG. 2, the crystal lattice constant is effectively extended in the off direction.

The off-angle of the off-substrate used as the support substrate 10 can be any size as long as it has an angle, but it is set to 0.1° or more and less than 45°, preferably 12.5° or less, so that the off-angle is sufficient to reduce the symmetry of the crystal structure at the main surface of the STO. By setting the off-angle in this manner, it becomes easier to align one of the two directions that can be aligned with the a-axis of FeNiN, making it easier to create a single variant in that direction.

However, if the off angle becomes too large, the number of monolayer steps 11 increases and the spacing between the monolayer steps 11 becomes narrower. It is more preferable to set the off angle taking this into consideration.

The interval of the monoatomic layer steps 11 is related to the width of the FeNi ordered alloy thin film 20. The single domain size of the L1 ₀ type FeNi ordered alloy is 50 to 200 nm, and if the size is smaller than the single domain size, it is difficult to create a magnetic domain and it is difficult to form a multi-domain state. That is, the narrower the interval of the monoatomic layer steps 11, the more difficult it is to create a magnetic domain and it is difficult to form a multi-domain state. Also, if the interval is larger than the single domain size of the L1 ₀ type FeNi ordered alloy, it is easy to generate magnetic domains with the magnetized direction facing in the opposite direction, and it is known that the coercive force Hc is best increased by setting the conditions to prevent this. That is, it is preferable that the interval of the monoatomic layer steps 11 is not larger than the single domain size. However, if the interval of the monoatomic layer steps 11 is too small compared to the single domain size, magnetization reversal is easy to occur due to thermal fluctuation, and the coercive force Hc is reduced. For this reason, in order for FeNiN, which is the precursor of the _L10 type FeNi ordered alloy, to have this size, the spacing between the monoatomic layer steps 11 is equal to or less than the single magnetic domain size of about 50 to 200 nm, and the average number of steps per specified area is set to be within a specified range so as not to be too small.

The average number of steps is expressed as the average number of steps per 1 μm, for example, and is about 6 when the off angle is 0.1° or more. When the number of steps per 1 μm is 6, the spacing between the monolayer steps 11 is 167 nm, which is the size of a single magnetic domain. Therefore, it is preferable to set the average number of steps per μm to 6 or more, that is, the off angle to 0.1° or more, so that the spacing between the monolayer steps 11 is equal to or smaller than the size of a single magnetic domain. Also, it is preferable to set the average number of steps to 20, that is, the off angle to 0.5° or less, so that the spacing between the monolayer steps 11 is not too small compared to the size of a single magnetic domain.

The FeNi ordered alloy thin film 20 is composed of an L1 ₀ type FeNi ordered alloy having an L1 0 type ordered structure. If the L1 ₀ type FeNi ordered alloy _thin film 20 is provided on the main surface of the support substrate 10, the tetragonal thin film structure becomes an FeNi ordered alloy structure including an FeNi superlattice. Such an FeNi ordered alloy structure is applicable to magnetic materials and device materials such as magnetic recording and magnetic sensors, and has excellent magnetic properties with high coercive force.

As shown in Figs. 1A and 1B, the FeNi ordered alloy thin film 20 is a thin film having a uniaxial in-plane orientation in contact with the main surface of the support substrate 10. Specifically, the FeNi ordered alloy thin film 20 is mainly formed between the monoatomic layer steps 11 formed on the main surface of the support substrate 10, and the slits 21 are formed at positions corresponding to each monoatomic layer step 11. The slits 21 are formed at positions corresponding to each monoatomic layer step 11, but are not necessarily formed at positions that completely match the monoatomic layer steps 11, and may not be formed corresponding to all monoatomic layer steps 11. The slits 21 may be formed shifted from each monoatomic layer step 11 in the same direction or in the opposite direction to the off direction, but are formed in a layout corresponding to the layout of the monoatomic layer steps 11. The slits 21 may be formed to penetrate the FeNi ordered alloy thin film 20 in the thickness direction, but are formed to a depth of 1/2 or more of the thickness of the FeNi ordered alloy thin film 20.

The c-axis is perpendicular to the off-direction of the support substrate 10, and each part of the FeNi ordered alloy thin film 20 separated by the slits 21 is arranged so that the c-axis direction is parallel.

This FeNi ordered alloy thin film 20 is manufactured by forming a thin film of a material containing elements Fe, Ni, and N, such as FeNiN, on the main surface of the support substrate 10, and then performing a denitrification process. In the case of FeNiN, the lattice constant on the a-axis of FeNiN(100) is 0.4002 nm, and the lattice constant on the c-axis of FeNiN(001) is 0.3713 nm. When forming a thin film of FeNiN, it is possible to obtain a thin film of FeNiN by a method of depositing FeNi on the support substrate 10 in a nitriding plasma, or by a method of depositing Fe and Ni layers alternately and then performing a nitriding process.

In addition, when the FeNi ordered alloy thin film 20 is formed from FeNiN, the lattice mismatch with FeNiN (100) is reduced because the support substrate 10 has an off-angle. Specifically, when the support substrate 10 does not have an off-angle, the lattice mismatch between STO (100) and FeNiN (100) is 2.484%, but when the support substrate 10 has an off-angle of 0.25° in the [010] direction, for example, the lattice mismatch between STO and FeNiN (100) is reduced to 2.483%. On the other hand, when the support substrate 10 does not have an off-angle, the lattice mismatch between STO (100) and FeNiN (001) is 4.917%, but when the support substrate 10 has an off-angle of 0.25°, the lattice mismatch between STO and FeNiN (001) increases to 4.918%. This makes it easier for the c-axis of FeNiN to be parallel to the monolayer steps 11, that is, perpendicular to the off-direction.

Here, the tetragonal thin film structure of this embodiment will be compared with the conventional case where a tetragonal thin film is formed on the main surface of STO (100). Here, an example is taken of a case where an FeNiN thin film is formed on a support substrate 10 made of STO. In the following explanation, the structure where an FeNiN thin film is formed on the main surface of STO (100) will be referred to as the comparative structure.

As shown in Figure 3A, in a comparative structure in which an FeNiN thin film J20 is formed on a support substrate J10 made of a substrate that does not have an off-angle with respect to STO (100), two types of variants are formed in which the c-axes of FeNiN intersect at 90°, as shown in Figure 3B. When TEM observations were performed, the dimensions of each variant were found to be small and miniaturized at up to 5 nm.

As shown in (a) of FIG. 2, STO has a cubic crystal structure. For this reason, the STO (100) used in the support substrate J10 in the comparative structure has four-fold symmetry, in which the same lattice structure is obtained every time it rotates 90° around the central axis, as can be seen from (b) of FIG. 2. In contrast, in the structure of this embodiment, the main surface used in the support substrate 10 has an off-angle in the [010] direction relative to (100), and as can be seen from (e) of FIG. 2, the structure is close to two-fold symmetry, in which the same lattice structure is obtained every time it rotates 180° around the central axis.

As shown in FIG. 4, in a comparative structure using STO(100) as the support substrate J10, the axes of STO(100) are aligned with the a-axis of FeNiN(100), and FeNiN(100) is epitaxially grown on the support substrate J10. Since STO(100) is a cubic crystal, the atomic arrangement and lattice constants of the mutually orthogonal axes are the same.

Therefore, when growing FeNiN using a support substrate J10 with a cubic crystal and a main surface with a (100) plane orientation, there are two axial directions that match the FeNiN, that is, there are two growth directions. For this reason, as shown in Figures 3A and 3B, there are two variants in which the c-axes of the FeNiN that make up the FeNiN thin film J20 intersect at 90°.

In contrast, when an off-substrate of STO having an off-angle in the [010] direction with respect to the (100) plane is used as the support substrate 10, the alignment with FeNiN is limited to one axis. Specifically, in a main surface having an off-angle of 12.5° with respect to STO (100), the lattice mismatch with FeNiN (100) is reduced from 2.480% when there is no off-angle to 0.050%. On the other hand, the lattice mismatch with FeNiN (001) is increased from 4.917% when there is no off-angle to 7.170% when there is an off-angle of 12.5°. Therefore, when FeNiN is grown using STO having an off-angle with respect to the (100) plane as the support substrate 10, the axial direction that is aligned with FeNiN is limited to one, that is, the growth direction is limited to one direction. As a result, the FeNiN becomes a single variant in which the c-axis is oriented in one direction, and the FeNi ordered alloy thin film 20 made of an _L10 type FeNi ordered alloy obtained by performing a denitrification treatment thereon also becomes a single variant in which the c-axis is oriented in one direction, as shown in Figures 1A and 1B.

In this way, by forming the FeNi ordered alloy thin film 20 on the support substrate 10 using an off-substrate whose main surface has an off-angle with respect to the (100) plane, the crystal of the FeNi ordered alloy thin film 20 can be made to be a single variant. Therefore, it is possible to obtain a tetragonal thin film structure with better properties. Note that the FeNi ordered alloy thin film 20 does not need to be a single variant throughout its entirety, and it is preferable to obtain a single variant with a large dimension, for example, 17 nm or more, preferably 30 nm or more. In other words, it is acceptable for there to be parts of other variants in parts, but it is preferable that the dimensions of the single variant parts are sufficiently larger than the dimensions of the other parts.

Next, comparative examples 1 to 3 in which the deposition conditions of the FeNi film were changed for the comparative structures shown in FIG. 3A and FIG. 3C, and examples 1 and 2 in which the deposition conditions of the FeNi film were changed using STO with a main surface having an off-angle in the [010] direction with respect to the (100) plane as the support substrate 10 were examined. FIG. 5 is a table showing the results. In the figure, "morphology" indicates the morphology of the FeNi film based on the deposition method, "FeNi ratio" indicates the ratio of Fe and Ni contained in the FeNiN film, and "support substrate" indicates the type of substrate used as the support substrate 10 and J10. "Average step" is the average value of the number of monolayer steps per μm of the support substrate 10 and J10, and the number of monolayer steps per μm is measured in the off direction for the off substrate with an off-angle, and in the direction in which the steps are arranged for the substrate without an off-angle. "Slit" indicates the presence or absence of slit 21 in the FeNi film. "Nitriding/Denitriding" indicates whether nitriding or denitriding is performed when the FeNi film is formed. "Designed film thickness" is the average film thickness of the FeNi film. "L1 ₀ (TEM)" indicates whether the L1 ₀ type structure is confirmed by TEM image analysis. "Hc [Oe]" and "Hc [kA/m]" indicate the coercive force in different units. "Hc [Oe] at 10K" and "Hc [kA/m] at 10K" indicate the coercive force at 10K (Kelvin) as the coercive force at extremely low temperatures with almost no thermal fluctuation.

In Comparative Example 1, Fe and Ni are simultaneously deposited in nitrogen plasma to form an FeNiN film. In Comparative Examples 2 and 3 and Examples 1 and 2, Fe and Ni are alternately deposited in atomic layers to form an FeNi film. In all cases, the FeNi ratio was 50:50.

In Comparative Examples 1 to 3, a substrate with no off-angle of STO (100) was used as the support substrate J10, and in Examples 1 and 2, an off-angle substrate with an off-angle of 0.10° and 0.25° with respect to STO (100) was used as the support substrate 10. In Comparative Examples 1 to 3, the average number of steps was 2, while in Example 1, the average number of steps was 6, and in Example 2, the average number of steps was 10. Since it is difficult to make the substrate surface completely flat, monolayer steps are present in Comparative Examples 1 to 3 as well, but since there is no off-angle, the average number of steps is sufficiently smaller than in Examples 1 and 2, and the step formation positions are also random. On the other hand, the STO with an off-angle used in Examples 1 and 2 had monolayer steps 11 at approximately equal intervals as shown in Figures 6A and 6B. In addition, as shown in Figure 6C, it was confirmed that slits 21 were formed in the FeNi ordered alloy thin film 20 at positions corresponding to the monolayer steps 11 in Example 1, and the same was true for Example 2.

In Comparative Example 1, no slits were formed in the FeNi film, whereas slits were formed in Comparative Examples 2 and 3 and Examples 1 and 2. For example, in Example 2, as shown in the cross-sectional TEM image of FIG. 7, slits 21 were formed in the FeNi ordered alloy thin film 20 composed of the FeNi film, with a depth of at least half the thickness. The positions at which the slits were formed corresponded to the width of the monoatomic layer steps.

As for the nitriding and denitriding treatments, only the denitriding treatment was performed in Comparative Example 1, neither was performed in Comparative Example 2, and both were performed in Comparative Example 3 and Examples 1 and 2. As for the designed film thickness, only Comparative Example 1 had a different form of FeNi film formation, so the thickness was 10 nm, but Comparative Examples 2 and 3 and Examples 1 and 2 had a thickness of 25 nm. Furthermore, as for L1 ₀ (TEM), only Comparative Example 2 did not have an L1 ₀ type structure, but Comparative Examples 1 and 3 and Examples 1 and 2 had an L1 ₀ type structure.

The coercive force Hc [Oe] was 126 [Oe] for Comparative Example 1 and 380 [Oe] for Comparative Example 2, and the coercive force Hc [kA/m] was 10.0 [kA/m] for Comparative Example 1 and 30.2 [kA/m] for Comparative Example 2, which were small values. In other words, when forming an FeNi film using STO (100) as the support substrate J10, only a small coercive force Hc was obtained when only the denitrification process was performed or when neither the nitridation process nor the denitrification process was performed.

In Comparative Example 3, the coercive force Hc [Oe] was 2390 [Oe] and the coercive force Hc [kA/m] was 190.2 [kA/m], which were large values. In other words, although the FeNi film was formed using STO (100) as the support substrate J10, a large coercive force Hc was obtained because nitridation and denitrification processes were performed.

On the other hand, in Example 1, the coercive force Hc [Oe] was 2420 [Oe], and the coercive force Hc [kA/m] was 192.6 [kA/m]. Furthermore, in Example 2, the coercive force Hc [Oe] was 2520 [Oe], and the coercive force Hc [kA/m] was 200.5 [kA/m]. If the coercive force Hc can be increased, a tetragonal thin film structure with a structure having better characteristics will be obtained. In Comparative Example 3, a large coercive force Hc is obtained by performing the nitriding process and the denitriding process, but if a larger coercive force Hc is obtained, a tetragonal thin film structure with a structure having better characteristics can be obtained. And, as in Examples 1 and 2, when an off-substrate having an off-angle with respect to STO (100) is used as the support substrate 10, a larger coercive force Hc can be obtained than when a substrate without an off-angle is used. Therefore, by using an off-substrate with an off-angle relative to STO (100) as the support substrate 10, it is possible to obtain a tetragonal thin film structure with superior properties.

Furthermore, when the relationship between the magnitude of the off angle and the coercive force Hc [Oe] is plotted based on Comparative Example 3 and Examples 1 and 2 shown in FIG. 5, the graph shown in FIG. 7 is obtained. As shown in this figure, there is a tendency that the larger the off angle, the larger the coercive force Hc. This is thought to be because the symmetry of the crystal structure on the main surface of the STO decreases as the off angle increases, and it no longer has four-fold symmetry. Furthermore, it is thought that the effect of the step spacing approaching the single magnetic domain size is also at work. Therefore, by increasing the off angle, a tetragonal thin film structure can be obtained that has a high coercive force Hc.

However, as mentioned above, if the off angle is too large, the number of monolayer steps 11 increases and the spacing between the monolayer steps 11 becomes narrow. Therefore, in order to ensure a certain width for the formation of the FeNi ordered alloy thin film 20 while reducing the symmetry of the crystal structure on the main surface of the STO, it is advisable to set the off angle to less than 45°, preferably 12.5° or less. More preferably, it is more preferable to set it to 0.5° or less.

In addition, the variant size of the FeNi ordered alloy thin film 20 was investigated using the cross-sectional TEM image shown in Fig. 8. Specifically, a cross-sectional sample sliced by focused ion beam (FIB) processing was subjected to high-resolution TEM observation from the STO[001] direction. The scan range was set to 17 nm, and the TEM image obtained in the scan range was subjected to Fourier transform (FFT) analysis, confirming the L1 ₀ -FeNi(001) diffraction spot, i.e., a spot indicating that FeNi is oriented along the c-axis.

Figures 9A to 9C show the results of TEM electron beam diffraction in regions A to C in Figure 8, respectively. Regions A to C are each in the range of 17 x 17 nm.

In each figure, the bright dots arranged in a lattice pattern represent the basic reflection pattern, and the white dot at the tip of the white arrow located at the center of one of the basic reflection diffraction spot patterns arranged in a square shape of the lattice represents the superlattice reflection diffraction spot pattern. When this superlattice reflection diffraction spot pattern appears, it indicates that the c-axis of L1 ₀ -FeNi is perpendicular to the paper surface.

In addition, in FIG. 9A, the white dots located between adjacent basic reflection diffraction spot patterns indicated by black arrows represent a state in which the c-axis lies in the plane, that is, the stacking structure of FeNi crystals is arranged with the left-right direction in the figure as the stacking direction, and the c-axis is located in that direction. For region A in FIG. 8, not only the superlattice reflection diffraction spot pattern in which the c-axis of L1 ₀ -FeNi is perpendicular to the paper surface, but also the c-axis is shown in the left-right direction in the figure. This means that it is oriented in two directions, and it can be seen that region A is multi-variant. On the other hand, for regions B and C in FIG. 8, only the superlattice reflection diffraction spot pattern in which the c-axis of L1 ₀ -FeNi is perpendicular to the paper surface appears. This means that it is oriented in one direction, and it can be seen that regions B and C are single variant.

In this way, the diffraction spot pattern of the superlattice reflection appears over an area of 17 x 17 nm or more, and single variants with dimensions of at least 17 nm or more that create this diffraction spot pattern have been obtained. Specifically, measurements showed that the dimensions of the single variants were 30 nm or more. The fact that single variants were obtained with such large dimensions is also thought to be the reason why the large coercive force Hc value described above was obtained.

As explained above, even if some of the FeNi constituting the FeNi ordered alloy thin film 20 is multi-variant, a single variant is obtained over a wider range. Therefore, it can be said that by using an off-substrate whose main surface has an off-angle with respect to the (100) plane as the support substrate 10 and depositing the FeNi ordered alloy thin film 20 on the support substrate 10, the crystals of the FeNi ordered alloy thin film 20 can be made to be single variant.

Other Embodiments
Although the present disclosure has been described based on the above-mentioned embodiment, it is not limited to the embodiment, and includes various modifications and modifications within the equivalent range. In addition, it is not limited to the magnetic material, and various combinations and forms, and further, other combinations and forms including only one element, more than one element, or less than one element, are also included in the scope and concept of the present disclosure.

For example, in the above embodiment, an off-substrate having a predetermined off-angle with respect to STO(100) is given as an example of a crystal structure belonging to a cubic crystal system constituting the support substrate 10, but the support substrate 10 may be made of other materials. For example, an off-substrate having a predetermined off-angle with respect to a metal oxide such as LAO(100) or MgO(100) may be used as the support substrate 10. The off-angle direction is not limited to the [010] direction, and may be any direction that reduces symmetry, such as a direction rotated 30° in-plane from the [010] direction.

10 Support substrate 20 FeNi ordered alloy thin film

Claims (9)

A support substrate (10) having a main surface on which monolayer steps (11) are formed and which has a predetermined off angle with respect to a (100) plane and a crystal structure belonging to a cubic crystal system;
a thin film (20) of an _L10 type FeNi ordered alloy formed on the main surface of the support substrate, in which a slit (21) is formed and which has a width corresponding to the monoatomic layer step ;
A tetragonal thin film structure, wherein the number of monolayer steps per 1 μm in the off-direction of the supporting substrate is 6 or more . A support substrate (10) having a main surface on which monolayer steps (11) are formed and which has a predetermined off angle with respect to a (100) plane and a crystal structure belonging to a cubic crystal system;
A slit (21) is formed on the main surface of the support substrate, and the slit (21) has a width L1 corresponding to the monoatomic layer step. ₀ and an FeNi ordered alloy thin film (20) composed of an FeNi ordered alloy of type
A tetragonal thin film structure, wherein the off angle in the supporting substrate is 0.1° or more and less than 45°. A support substrate (10) having a main surface that is at a predetermined off angle with respect to the (100) plane and a crystal structure belonging to a cubic crystal system;
A slit (21) is formed on the main surface of the support substrate, L1 ₀ and an FeNi ordered alloy thin film (20) composed of an FeNi ordered alloy of type
A tetragonal thin film structure, wherein the off angle in the supporting substrate is 0.1° or more and less than 45°. 2. The tetragonal thin film structure according to claim 1 , wherein the off-angle in the supporting substrate is 0.1° or more and less than 45°. 2. The tetragonal thin film structure according to claim 1 , wherein the off-angle in the supporting substrate is 0.1° or more and 12.5° or less. 2. The tetragonal thin film structure according to claim 1 , wherein the off-angle in the supporting substrate is 0.1° or more and 0.5° or less. 7. A tetragonal thin film structure according to claim 1, wherein said supporting substrate is made of _SrTiO3 . The tetragonal thin film structure according to any one of claims 1 to 7, wherein the slits are formed in the FeNi ordered alloy thin film with a depth of at least 1/2 the thickness of the FeNi ordered alloy thin film. The tetragonal thin film structure according to any one of claims 1 to 8, wherein the FeNi ordered alloy thin film has a single variant with a dimension of 17 nm or more.

Images