JPS6216268B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an amorphous soft magnetic thin film, and in particular, the present invention relates to a method for manufacturing an amorphous soft magnetic thin film, and in particular, the present invention relates to a method for manufacturing an amorphous soft magnetic thin film. The present invention relates to a method of manufacturing a magnetic thin film.

The amorphous magnetic material is formed by an ultra-quenching method, a sputtering method, a vapor deposition method, a plating method, or the like. The ultra-quenching method generally forms a relatively thick ribbon of about 20 to 100 μm, but the sputtering method, vapor deposition method, and plating method are methods suitable for obtaining thin film materials of several μm or less.

An amorphous soft magnetic material (hereinafter simply referred to as an amorphous magnetic material) does not have a plurality of constituent elements arranged in a regular arrangement, so it essentially does not have magnetocrystalline anisotropy. However, in reality, magnetic anisotropy exists due to the arrangement of magnetic atoms and magnetostriction in the microscopic region.
In the as-manufactured state, the magnetic properties are often insufficient for practical use. Furthermore, the amorphous state itself is just one metastable state, and it changes to another metastable state by heating, etc., and the magnetic properties change accordingly. The stability is also poor. Therefore, in many cases, amorphous magnetic materials are used after being annealed. Various methods are known as annealing methods for this purpose.

The most commonly used annealing method for ultra-quenched ribbons is a method of annealing in a non-magnetic field, and such a method is disclosed in JP-A-52-114421 and other publications. In this case, in order to prevent magnetic anisotropy from being induced by annealing, the annealing temperature must be higher than the Curie temperature, while of course the annealing must be performed at a temperature lower than the crystallization temperature. It is. Therefore, unless the material is an amorphous magnetic material whose crystallization temperature is higher than the Curie temperature, carrying out such an annealing method is not only meaningless but also harmful in some cases.

For amorphous materials whose crystallization temperature is lower than the Curie temperature, a magnetic field annealing method has been developed, and this annealing method is disclosed, for example, in Japanese Patent Application Laid-open Nos. 51-73925 and 1982-114421. There is. In the case of these annealing in a magnetic field, since the magnetic field is a unidirectional magnetic field, uniaxial induced magnetic anisotropy is induced, and excellent magnetic properties are obtained in the ultra-quenched ribbon. However, for amorphous thin films such as cobalt-zirconium or iron-cobalt-silicon-boron formed by the sputtering method, the anisotropic magnetic field does not become much smaller and the magnetic permeability does not increase when this annealing method is applied. It is disclosed in Japanese Patent Publication No. 1983-66611. In addition, methods for annealing amorphous magnetic materials in a rotating magnetic field are disclosed in Japanese Patent Laid-Open Nos. 55-152164, 5959-5962, 44746, 98465, and so on. has been disclosed. All of these methods aim to obtain isotropic properties without producing magnetic anisotropy in a particular direction of the material, and these methods have provided excellent magnetic properties. Such an annealing method in a rotating magnetic field is also effective as an annealing method for amorphous soft magnetic films formed by the sputtering method, as reported in Japanese Patent Application Laid-Open No. 57-66611 and in the literature (6th Academic Conference of the Japan Society of Applied Magnetics). Abstracts 15pB-7 (1982)). Annealing an amorphous magnetic thin film in a rotating magnetic field does not necessarily result in isotropic magnetic properties, but the magnetic anisotropy formed during film formation has high magnetic permeability in the direction of the difficult axis of magnetization, resulting in anisotropy. Characteristics with small magnetic field can be obtained.

Institute of Electronics and Communication Engineers Electronic Materials Components and Materials Study Group
CPM81-11 (1981) discloses the following annealing method. In other words, this annealing method applies a relatively strong magnetic field in one direction to a cobalt-zirconium thin film formed by the sputtering method, anneales it to generate uniaxial magnetic anisotropy, and then applies a weak magnetic field in a direction perpendicular to the annealing. This is a method of distributing magnetic anisotropy and obtaining highly isotropic properties by annealing.

JP-A-56-112450 discloses a method of generating multiaxial magnetic anisotropy by annealing in a magnetic field. In this method, the sample is rotated by a predetermined angle at predetermined time intervals to perform annealing.

As described above, the conventionally known annealing method is an annealing method that suppresses the formation of clear uniaxial magnetic anisotropy. As mentioned above, in the case of amorphous soft magnetic thin films, the uniaxial magnetic anisotropy formed during film formation does not completely disappear, but the purpose is the same. However, in some applications, it may be advantageous to form clear uniaxial magnetic anisotropy in any desired direction. For example, when a magnetic thin film is applied to a magnetic head, it is generally used by imparting uniaxial magnetic anisotropy to form a magnetic path in the direction of the difficult axis of magnetization. The reasons for this are that the speed of magnetization reversal is faster and it operates better at high frequencies when magnetization is rotated than by domain wall movement, the permeability is higher in the direction of the difficult axis than in the direction of the easy axis, and For example, there is less noise at the time. When a magnetic thin film is used in a magnetic head, it is necessary to have a small anisotropic magnetic field in order to increase the recording sensitivity, and it is desirable that the magnetic permeability in the hard axis direction be high in order to increase the reproduction efficiency. In particular, in a perpendicular head used for perpendicular magnetic recording, the higher the magnetic permeability, the higher the reproduction output, so it is effective to increase the magnetic permeability.

As will be described later, the axis of easy magnetization of the magnetic anisotropy formed during film formation by the sputtering method differs depending on the location within the film plane. This shows that it is difficult to form uniform uniaxial magnetic anisotropy over a wide area in any desired direction. Therefore, even if such an amorphous magnetic thin film is annealed in a rotating magnetic field, uniaxial magnetic anisotropy cannot be formed in any direction. The advantage of forming uniaxial magnetic anisotropy in any direction is particularly large as a mass production effect, and it is possible to perform annealing to form magnetic anisotropy after finely processing the magnetic thin film.

Now, JP-A-54-122000 describes that an amorphous magnetic thin film is annealed in an external magnetic field in order to stabilize the axis of easy magnetization and obtain low coercive force and high magnetic permeability. A stable easy axis is obtained by annealing in an external unidirectional magnetic field for a long time (eg, 16 hours at about 250°C, 1 hour at about 350°C). As a measure of the stability of the easy axis, annealing is performed by applying a magnetic field in the direction of the hard axis at a temperature lower than the above annealing temperature, and the length of annealing time until formation of a new easy axis occurs. However, according to this method, as described in JP-A-57-66611, etc., it is difficult to obtain magnetic permeability as high as that obtained by annealing in a rotating magnetic field.

The present invention has been made in view of the above-mentioned current situation, and it is possible to generate a clear uniaxial magnetic different direction in any direction of an amorphous soft magnetic thin film, and to create a material with high magnetic permeability in the difficult axis direction. It is an object of the present invention to provide a method for manufacturing an amorphous soft magnetic thin film (hereinafter referred to as an amorphous magnetic thin film) with a small directional magnetic field.

The method of annealing an amorphous magnetic thin film according to the present invention is carried out as follows. That is, an amorphous magnetic thin film formed by a sputtering method is placed in a vacuum or an inert gas, and a DC magnetic field is applied in a certain direction within the film surface, and then the first annealing is performed. Of course, the annealing temperature at this time must be lower than the crystallization temperature, but it is also necessary to ensure that the first annealing does not form a new axis of easy magnetization in the direction of the applied magnetic field. It is desirable to keep the annealing temperature and annealing time within limits. However, this is not an absolute condition.
Specifically, a temperature of 200°C or higher and around 360°C is desirable. 200
At temperatures lower than ℃, there is almost no effect of annealing,
Furthermore, when annealing at temperatures above 360°C, the formation of an axis of easy magnetization in a new direction occurs in a short period of time, which is difficult to control. 1st
The effect of the second annealing is to eliminate the magnetic anisotropy of the component perpendicular to the magnetic film plane, which is perpendicular to the film plane, and at the same time, it is probably necessary to carry out the second annealing to improve the magnetic permeability. This is thought to be effective in stabilizing the axis of easy magnetization of seeds. This will be explained later in Examples, but if the first annealing is performed at such a low temperature that a new axis of easy magnetization can be formed in the direction of the applied magnetic field in an extremely short time during the second annealing, the magnetic permeability will increase. This is because it doesn't get too expensive.
Therefore, the first annealing is preferably at 300°C or higher,
It is desirable that the annealing temperature be slightly lower than the second annealing temperature. Next, the amorphous thin film is rotated 90 degrees within the plane, and a second annealing is performed by applying a magnetic field in a direction perpendicular to the direction of the first applied magnetic field. The annealing temperature at this time is higher than the first annealing temperature. On the other hand, the annealing time is appropriately selected and the annealing is stopped as soon as possible when a new axis of easy magnetization occurs in the direction of the applied magnetic field. In some cases, the direction of the direct current magnetic field may be further changed by 90 degrees within the film plane, and the third annealing may be performed at the same temperature as the second annealing, or at a slightly higher temperature. The reason why annealing is stopped immediately when a new easy axis is formed in the direction of the applied magnetic field in the second and subsequent annealing is that if annealing is continued further, the anisotropic magnetic field increases and the permeability decreases. This is because it will be put away. The second and subsequent annealing temperatures are for the examples described below.
The temperature is about 360-380℃. These optimum annealing temperatures vary depending on the composition of the amorphous thin film material.

By the way, JP-A-57-66611 describes that when magnetic anisotropy is induced by annealing in a DC magnetic field, the magnetic permeability increases and the anisotropic magnetic field becomes considerably large. However, this method is clearly different from the method of the present invention in that annealing is performed only once. Also, according to the literature (6th Japanese Society of Applied Magnetics Academic Conference Abstracts, 15pB-7 (1982)), a cobalt-zirconium film is annealed in a direct current magnetic field, and then a magnetic field is applied in the perpendicular direction to the same temperature. It is stated that when annealed at , the magnetic permeability shows a maximum value with respect to the annealing time. It is also stated that this maximum value of magnetic permeability is smaller than that in the case of annealing in a rotating magnetic field. This case differs from the method of the present invention in that the two annealings are performed at the same temperature and that the second annealing does not form an axis of easy magnetization in the direction of the applied magnetic field.

Next, the present invention will be explained in detail with reference to the drawings.

Although the present invention does not specify the composition of the amorphous magnetic thin film, an amorphous magnetic thin film made of cobalt-niobium-zirconium having a high saturation magnetic flux density and a zero magnetostriction composition will be selected and explained below.
The sample was formed on a glass substrate by a known high frequency sputtering method. 5 mm square niobium and zirconium pellets were uniformly arranged on a 5 inch diameter cobalt target, and a high frequency power density of 0.8 to 1.6 W/cm ² was applied.
A magnetic thin film with a thickness of 0.2 to 0.4 μm was formed under an argon pressure of 2.5 to 10 mmTorr. Although the substrate holder is water-cooled, the surface temperature of the substrate during sputtering is 100 to 150°C. The composition of the formed film is approximately
Co _{85 Nb 10.0} Zr _4.5 , the saturation magnetic flux density is 10000 Gauss, and the magnetostriction constant is _a small negative value. As a result of examination by X-ray diffraction, only a halo pattern was observed, and it was confirmed that the obtained film was substantially amorphous. The crystallization temperature determined by the temperature change of magnetization is
Although the temperature was 460°C, it was confirmed by microscopic observation that local crystallization occurred when annealing at 390°C for 1 hour.

Uniaxial magnetic anisotropy occurs in the amorphous magnetic thin film formed by the above method due to the influence of earth's magnetism, and the magnetic permeability is almost in the direction of the hard magnetization axis.
200, which was too small to be measured in the easy magnetization axis direction. Note that magnetic permeability was measured using a Q meter at 500kHz. It has been found that the direction of magnetic anisotropy induced during film formation differs depending on the position of the substrate placed during sputtering. This shows that it is not only the geomagnetism that contributes to the formation of magnetic anisotropy. FIG. 1 is a diagram showing the results of forming a sputtered film on a slide glass used as a substrate, cutting it into 6 mm square pieces, and measuring the magnetic permeability of each cut piece in two orthogonal directions. This sample was obtained from a portion of the substrate 2 placed at the position shown in the figure with respect to the target 1 in FIG. 2 during sputtering. In FIG. 1, the arrows indicate the magnitude of magnetic permeability measured in each direction, with the largest arrow indicating a magnetic permeability of about 200, and the other arrows indicating proportionally smaller values. As is well known, when uniaxial magnetic anisotropy occurs, magnetic permeability is smallest in the easy magnetization direction and largest in the hard axis direction. Therefore, the results shown in FIG. 1 show that the direction of the axis of easy magnetization differs depending on the location, indicating that the magnetic anisotropy formed during film formation is not solely due to the influence of earth's magnetism.
This also indicates that when forming an amorphous magnetic film by the sputtering method, it is difficult to form uniaxial magnetic anisotropy in a uniform direction over a wide area.

Examples of the present invention will be described below along with comparative examples.

Comparative Example 1 A DC magnetic field of 3 kOe was applied in a direction close to the easy magnetization direction formed during film formation by the sputtering method, and the first annealing was performed at 360°C in vacuum for 1 hour.
The sample was rotated 90° in the film plane and heated at 360°C in a 3kOe magnetic field.
A second annealing was performed. The magnetic permeability μ at this time was measured in the magnetic different direction during the second annealing, that is, in a direction close to the direction of the hard magnetization axis formed during film formation, and is shown against the second annealing time t. FIG. The magnetic permeability tends to increase and become saturated with respect to the second annealing time. Further, the axis of easy magnetization formed during film formation did not change its direction even after the second annealing. As expected from other examples, increasing the second annealing time should result in new formation of an easy axis of magnetization in the direction of the magnetic field. The magnetic permeability in Figure 3 is not very high.

Example 1 The first annealing was performed at 300°C for 30 minutes by applying a DC magnetic field of 3 kOe in a direction close to the direction of easy magnetization during film formation, and then the sample was rotated 90° within the film plane.
A second annealing was performed at 360° C. for t minutes by applying a DC magnetic field of 3 kOe. FIG. 4 shows the magnetic permeability measured in two directions with respect to the annealing time t. The solid line indicates the magnetic field direction during the second annealing, and the dotted line indicates the magnetic permeability in a direction perpendicular to the magnetic field direction. The magnetic permeability shown by the solid line increases with the annealing time t, reaching about 2600 at t=120 minutes, and rapidly decreases when t>120 minutes, reaching a small value of about 100 at t=160 minutes. On the other hand, the magnetic permeability shown by the dotted line increases rapidly when t>120 minutes, reaches about 2750 at t=150 minutes, and gradually decreases thereafter. Such changes in magnetic permeability in two orthogonal directions indicate that a new uniaxial easy axis of magnetization was formed in the direction of the last applied magnetic field during the annealing time of 130 to 150 minutes.

Although the second annealing conditions of this example are the same as those of Comparative Example 1, a much higher magnetic permeability than that of Comparative Example 1 is obtained. In this example, this is the effect of making the first annealing temperature lower than the second annealing temperature.

Example 2 After performing two times of annealing in exactly the same manner as in Example 1,
A magnetic field of 3 kOe was applied in the same direction as the applied magnetic field during the second annealing, and the temperature was raised to 370°C during the third annealing.
The second annealing was performed. FIG. 5 shows how the magnetic permeability μ changes with respect to the annealing time t. The solid line and the dotted line indicate the magnetic permeability in the direction of the third applied magnetic field and in the direction perpendicular thereto, respectively. The maximum value of magnetic permeability shown by the solid line is about 3000, but the maximum value in the case of the dotted line increases to nearly 4500. In this example, a new axis of easy magnetization is formed in the direction of the applied magnetic field by the third annealing between t = 50 and 60 minutes, and the magnetic permeability in the direction of the axis of hard magnetization at this time is The value is extremely high.

Figure 6 shows the hysteresis loop measured with a 1kHz AC hysteresis loop tracer.
b corresponds to the annealing time t=40 minutes in FIG. 5, and b corresponds to the annealing time t=60 minutes. In these figures, the solid line indicates the hysteresis loop in the direction of the applied magnetic field during the final annealing, and the dotted line indicates the hysteresis loop in the direction perpendicular to it. As mentioned above, it is clear that at an annealing time of t=60 minutes, an easy axis is formed in the direction of the magnetic field applied during the final annealing. When the anisotropic magnetic field is determined from the hysteresis loop in the direction of the hard magnetization axis in each figure, it is 3.5 Oe in Figure 6a and 2.5 Oe in Figure 6b, which is smaller in case b.

Comparative Example 2 The first annealing was performed at 300° C. for 1 hour by applying a magnetic field of 3 kOe in a direction close to the direction of easy magnetization during film formation. After that, the sample was rotated 90 degrees within the film plane, and a magnetic field of 3 kOe was applied in the direction perpendicular to the first time, and 370
A second annealing was performed at °C. FIG. 7 shows the relationship between the second annealing time t and the magnetic permeability μ. The solid lines and dotted lines are the same as in Example 1 and Example 2. In this case, the magnetic permeability in either direction is quite small.
It can be seen that an axis of easy magnetization is formed in the direction of the applied magnetic field at an annealing time of t=5 to 8 minutes. In this example, the reason for the low magnetic permeability is that there is a large difference between the first and second annealing temperatures, and the second annealing temperature was too high, causing the formation of a new axis of easy magnetization within an extremely short period of time. This is probably due to what happens.

In each of the above examples, during the second annealing, the sample was rotated by 90 degrees with respect to the direction of the DC magnetic field within the film plane, but the DC magnetic field was rotated without rotating the sample. You may let them.

Comparative Example 3 A conventionally known rotating magnetic field annealing method was carried out and compared with the annealing method according to the present invention. In this example, instead of rotating the direction of the magnetic field, the sample was rotated in a DC magnetic field. The rotation speed of the sample was 120 rpm, and the magnetic field strength was 3 kOe. FIG. 8 is a diagram showing the relationship between annealing time t and magnetic permeability μ performed at 360°C. At annealing time t=120 minutes, the magnetic permeability reaches its maximum and shows a value of about 3600. This value is comparable to or lower than the maximum permeability value shown by the dotted line in FIG.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the magnitude of magnetic permeability in two directions in each part of a magnetic film formed on a slide glass substrate, Figure 2 is a diagram showing the positional relationship between the sputter target and the slide glass substrate, and Figure 3 is a diagram showing the positional relationship between the sputter target and the slide glass substrate. The figure shows the relationship between annealing time t and magnetic permeability μ, and Figures 4 and 5 show the annealing time t and two directions orthogonal to each other within the film surface when annealing was performed three times corresponding to Example 2. Figure 6 is a diagram showing the hysteresis loop, Figure 7 is a diagram showing the relationship between the annealing time t and magnetic permeability μ measured in two directions within the film surface, and Figure 8 is a diagram showing the relationship between the magnetic permeability μ measured in two directions within the film surface. The figure shows the relationship between annealing time t and magnetic permeability μ in rotating magnetic field annealing.

Claims (1)

[Claims] 1. In a method for producing an amorphous soft magnetic thin film that exhibits excellent soft magnetic properties by annealing an amorphous magnetic thin film formed by a sputtering method once or twice in a magnetic field, firstly, , annealing is performed in a vacuum or inert gas by applying a DC magnetic field in the in-plane direction of the thin film in a direction close to the direction of the axis of relatively easy magnetization of the thin film, and then in the direction of the previously applied magnetic field in the same film plane. When annealing is performed by applying a DC magnetic field one or two more times in the orthogonal direction, the first annealing temperature is _T1 , the second and subsequent annealing temperatures are _T2 , _T0 , and the crystallization temperature is 1. A method for producing an amorphous soft magnetic thin film having uniaxial magnetic anisotropy, characterized in that the process is carried out under the conditions of T ₁ <T ₂ ≦T _o <T _X , where T _X . 2. In the above annealing, the initial annealing temperature _T1 and the annealing time are set under a direct current magnetic field so that new formation of an axis of easy magnetization does not occur in the direction of the applied magnetic field. The manufacturing method described in section.