JPH04332106A - Magnetostatic wave element - Google Patents

Abstract

PURPOSE:To obtain a magnetostatic wave element with a stable operation frequency even for a rapid temperature change by constituting a magnetic circuit using a permanent magnet with a specific temperature coefficient of residual magnetic flux density. CONSTITUTION:A title item consists of a magnetic garnet film 1 which is formed on a non-magnetic substrate, a coil 5, a yoke 3, and a permanent magnet 4 where a temperature coefficient of a residual magnetic flux density is -0.03--0.05(%/ deg.C) and then a magnetic circuit 2 which applies a DC magnetic field to the magnetic garnet film 1 vertically. Also, it is formed by a magnetic garnet where a temperature coefficient of an absolute value of the magnetic garnet film 1 is -1--1.5(Gauss/ deg.C). It is a liquid-phase epitaxial magnetic garnet film 1 which is suited for forming the magnetic garnet film 1 and is expressed by an expression I. The temperature coefficient of a gap magnetic field is determined only by that of a permanent magnet and a rate of temperature compensation is determined by the permanent magnet, thus enabling stable magnetic field to be generated for rapid temperature change by using the permanent magnet with a small temperature coefficient of residual magnetic flux density.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetostatic wave device used in the microwave band. More specifically, the present invention relates to a magnetostatic wave element whose operating frequency is stable even in the face of rapid temperature changes.

0002

[Prior art] Magnetostatic wave elements are made by growing a YIG (yttrium iron garnet) film on a GGG (gadolinium gallium garnet) single crystal substrate by liquid phase epitaxial growth, and processing the film into a desired shape using lithography and etching techniques. However, a micro strip line is formed. Such a magnetostatic wave element excites magnetostatic waves using microwaves while applying a DC magnetic field to YIG, and is considered to be used in resonators, filters, and the like. A magnetostatic wave element is characterized in that its operating frequency can be variably controlled by applying a DC magnetic field.

FIG. 7 shows, for example, Japanese Patent Application Laid-Open No. 1-191502.
1 is a diagram showing the configuration of a conventional magnetostatic wave element published in a publication. In FIG. 7, 1 is a YIG film, 2 is a magnetic circuit, 3 is a yoke, 4 is a permanent magnet, 5 is a coil, and 8 is a magnetic pole made of a soft magnetic material.

Next, the operation of the magnetostatic wave element having such a configuration will be explained. When a DC magnetic field H is applied in a direction perpendicular to the plane of the YIG film, the operating frequency f of the magnetostatic wave element is expressed by equation (1).

f=γ(H−N・4πMs) (1
) Here, 4πMs is the saturation magnetization (Gauss) of YIG,
γ is the gyromagnetic ratio (2.8 MHz/Oe), and N is the demagnetizing field coefficient. However, since the saturation magnetization of YIG is temperature dependent, there is a drawback that the operating frequency f changes depending on the temperature even if the DC magnetic field H is constant. Formula (1
), the condition where the operating frequency f does not depend on the temperature T is expressed by equation (2) with the demagnetizing field coefficient being 1.

[0006] δH/δT=δ4πMs/δT (2) That is, by making the temperature coefficient of the absolute value of the magnetic field equal to the temperature coefficient of the absolute value of the demagnetizing field due to YIG, changes in the operating frequency due to temperature can be compensated for. In this specification, the demagnetizing field due to YIG is defined as the saturation magnetization (Gau
ss). Also, temperature coefficient (%/℃
) and absolute temperature coefficient (Gauss/℃ or Oe/℃
) are listed separately. In Figure 7, permanent magnet 4
By causing temperature-related changes in the magnetic field of the gap to perform temperature compensation, and by passing current through the coil 5, the operating frequency can be variably controlled.

[0007]

[Problem to be Solved by the Invention] Since the conventional magnetostatic wave element is constructed as described above, the magnetic circuit and the magnetic thin film such as the YIG film are kept at the same temperature and temperature compensation is not performed against sudden temperature changes. The problem is that the operating frequency becomes unstable until the

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a magnetostatic wave element whose operating frequency is stable even under sudden temperature changes.

[0009]

[Means for Solving the Problems] The magnetostatic wave element of the present invention includes:
The temperature coefficient of the magnetic garnet film formed on the non-magnetic substrate, the coil, the yoke, and the residual magnetic flux density is -0.03.
-0.05 (%/℃), and a magnetic circuit that applies a direct current magnetic field perpendicularly to the magnetic garnet film, and the magnetic garnet film has a temperature coefficient of the absolute value of saturation magnetization of -1. It is characterized by being made of magnetic garnet with a temperature of -1.5 (Gauss/°C).

The magnetostatic wave element of the present invention uses a permanent magnet with a temperature coefficient of -0.03 to -0.05 (%/°C) in the magnetic circuit, and the temperature coefficient of the absolute value of saturation magnetization is -1 to -1. -1.
5 (Gauss/° C.), the operating frequency of a magnetic garnet film formed of magnetic garnet is temperature-compensated. Furthermore, the liquid phase epitaxial magnetic garnet film of the present invention is suitable for forming the above magnetic garnet film.

[0011]

[Operation] In order to stabilize the operating frequency against rapid temperature changes, it is necessary to stabilize the gap magnetic field generated by the permanent magnet, and to minimize the temperature coefficient of the absolute value of the gap magnetic field and the saturation magnetization of the YIG film. It is necessary to match the values.

FIG. 1 shows an embodiment of the magnetostatic wave element of the present invention, in which the cross-sectional area of the permanent magnet 4 is represented by S.
m, the thickness is 1 m/2, the cross-sectional area of the gap 7 is Sg, and the length is 1 g. In addition, the magnetic field generated by the permanent magnet 4 in the gap is Hg, the magnetic flux density is Bg, and the magnetic field inside the permanent magnet is Hm.
Let Bm be the magnetic flux density and σ be the leakage coefficient. Equation (3) holds for magnetic flux. However, the coil current is 0.

BgSgσ=BmSm
(3) According to Ampere's circuit theorem, Hg1g=Hm1m
(4) From formulas (3) and (4), Bm/Hm=μ0(Sgσ/Sm
) (1m/1g) (5) Considering the magnetostatic energy, BgHgSgσ1g=BmHmS
m1m (6) Here, if the coercive force of the magnet is large enough, the recoil permeability is set to 1.
It can be considered as The retained magnetic flux density of the permanent magnet is Br
Then, Bm=Br-μ0Hm

(7) From formulas (5), (6), and (7), Hg=1/(μ0(Sgσ/Sm
+1g/1m))・Br (8) Therefore, the temperature coefficient of the absolute value of the magnetic field in the gap is expressed by equation (9).

δHg/δT=1/(μ0(Sgσ/Sm
+1g/1m))・δBr/δT (9) Next, from formulas (8) and (9), (δHg/δT)/Hg=(δBr/δT
)/Br (10) From equation (10), it can be seen that the temperature coefficient of the magnetic field in the gap generated by the permanent magnet is determined only by the temperature coefficient of the residual magnetic flux density, regardless of the shape of the permanent magnet. Moreover, the magnetic garnet film 1 placed between the gaps is sufficiently small compared to the volume of the permanent magnet 4, and its heat capacity can be ignored. Therefore, with respect to temperature changes, the permanent magnet is rate-limiting until the magnetic circuit and the magnetic garnet film reach the same temperature and the operating frequency is temperature compensated.

The temperature coefficient of the gap magnetic field is determined only by the temperature coefficient of the permanent magnet, and the temperature compensation is rate-determined by the permanent magnet. For the above reasons, it can be seen that by using a permanent magnet with a small temperature coefficient of residual magnetic flux density, it is possible to generate a stable magnetic field in the gap against rapid temperature changes. Table 1 shows the characteristics of various commercially available permanent magnets. Sm-Co magnets and alnico magnets have a small temperature coefficient of residual magnetic flux density, and a stable magnetic field can be obtained by using either of them. However, in order to obtain a gap magnetic field of the required magnitude, it is desirable to configure the magnetic circuit with a permanent magnet having a large coercive force, and therefore it is preferable to employ an Sm--Co magnet. Note that the temperature coefficient range of these permanent magnets is -0.03 to -0.05 (%/°C).

[0016]

[Table 1] Regarding temperature compensation, it is desirable to match the temperature coefficient of the absolute value of the magnetic field of the gap and the saturation magnetization of YIG to a value as small as possible. As can be seen from equation (9), the temperature coefficient of the absolute value of the magnetic field in the gap can be adjusted by changing the cross-sectional area and length of the gap and the permanent magnet. However, in reality, its dimensions are limited by the size of the magnetic garnet film. For example, 10 to 1
In order to install a crystal with a 00 μm YIG film, the gap length must be 1 mm or more. Assuming that the ratio of the cross-sectional area of the gap to the permanent magnet is Sg/Sm = 0.5, the length of the gap is 2 mm, and the experimentally determined leakage coefficient σ = 4.5, the thickness of the permanent magnet is 1 m (Figure 1 Figures 2 and 3 show the results of calculating the temperature coefficient of the gap magnetic field (the sum of the lengths of the two permanent magnets), the gap magnetic field, and its absolute value. From Figure 3, when using Sm-Co magnets, the temperature coefficient of the absolute value of the magnetic field in the gap is -1.5 to 0 Oe/℃.
It can be seen that it can be set. However, it is possible to increase the temperature coefficient of the absolute value of the magnetic field in the gap by further reducing the value of Sg/Sm, but it is not desirable to reduce the cross-sectional area of the gap in order to obtain a uniform magnetic field. .

On the other hand, the temperature coefficient of the absolute value of the saturation magnetization of YIG is adjusted by replacing the magnetic element iron of the garnet component with the nonmagnetic element gallium. However, since the ionic radius of gallium is smaller than that of iron, it is necessary to replace a portion of yttrium with lanthanum, which has a larger ionic radius than yttrium, in order to match the lattice constant with the GGG substrate. Specifically, for example, high purity lead oxide, boron oxide, iron oxide, yttrium oxide, gallium oxide,
Lanthanum oxide powder is weighed, mixed, charged into a platinum crucible, heated to 1150°C to sufficiently melt, and then slowly cooled to a predetermined temperature and held. Next, a magnetic garnet film can be epitaxially grown by dipping the (111)-plane GGG single crystal substrate into a melt while rotating it horizontally. Table 2 shows the saturation magnetization, the temperature coefficient of its absolute value, and the composition of the YIG film produced as described above, and FIG. 4 shows the relationship between the saturation magnetization and the temperature coefficient of its absolute value.

[0018]

[Table 2] The temperature coefficient of the absolute value of saturation magnetization can be reduced by reducing the value of saturation magnetization. At the same time, since the demagnetizing field becomes smaller, the applied DC magnetic field can also be smaller, which has the advantage that magnetic circuits such as coils and permanent magnets can be made smaller. However, if the saturation magnetization becomes too small, the magnetostatic waves excited by the microwaves will become weak and the device will not function well. For example, the saturation magnetization is 4
If an oscillator is manufactured using a garnet film of 0.00 Gauss or less, the external Q will be large and it will be difficult to obtain good oscillation characteristics. Further, as can be seen from FIG. 4, the temperature coefficient of the absolute value of saturation magnetization does not change much, and the advantage of reducing saturation magnetization is lost. Therefore, the lower limit of the temperature coefficient of the absolute value of saturation magnetization is -1.0 Gauss/°C, and the value of saturation magnetization at this time is 400 Gauss.

Based on the above study of the magnetic circuit and the liquid phase epitaxial magnetic garnet film, the temperature coefficient of the absolute value of the saturation magnetization that can be matched is -1.0 to -1.5 Gauss/°C.
It turned out to be between. The composition of the magnetic garnet film represented in Table 2 is summarized as shown in formula (I).

Y3-zLazFe5-
tGatO12 t=10
z-0.54 (0.12≦z≦0.14)
(I)

[0021]

Embodiments Next, embodiments of the present invention will be described with reference to the accompanying drawings. In FIG. 1, 1 is a magnetic garnet film, 2 is a magnetic circuit, 3 is a yoke, 4 is a permanent magnet, 5 is a coil, and 6
is a magnetic pole, and 7 is a gap. In this example, the diameter of the permanent magnet is 8 m so that a uniform magnetic field is generated with a diameter of 3 mm.
The diameter of the gap was 6 mm. In this case, the cross-sectional area ratio Sg/Sm is 0.5625. Although the diameter of the permanent magnet and the diameter of the gap are not particularly limited in the present invention, they are usually both 4 to 20 mm, and the diameter of the gap is smaller than the diameter of the permanent magnet to concentrate the magnetic field. Further, the cross-sectional shape of the permanent magnet is not limited to a circle, but may be other shapes such as a rectangle.

[0022] As the yoke material, general structural rolled steel material, permalloy, etc. can be used, but in this embodiment, general structural rolled steel material SS41 was used as the yoke material. Although the permanent magnets shown in Table 1 can be used, magnet A was used in this example. To adjust the magnetic field in the gap, the magnetic field was measured by changing the length of the gap. FIG. 5 shows the relationship between the gap length 1 g and the magnetic field Hg, and FIG. 6 shows the relationship between the gap length 1 g and the temperature coefficient of the absolute value of the magnetic field Hg. The leakage coefficient of the produced magnetic circuit was found to be 4.5.

In Table 2, the temperature coefficient of the absolute value of saturation magnetization of YIG numbered 5 is -1.10 Gauss/°C. From FIG. 6, since the temperature coefficient of the absolute value of the magnetic field when the gap length is 2 mm is -1.10 Oe/°C, temperature compensation can be performed. When the operating frequency of the obtained magnetostatic wave element was measured, it was 4.73 GHz when the coil current was 0.

[0024]

[Effects of the Invention] As explained above, according to the present invention,
Temperature coefficient of residual magnetic flux density is -0.03 to -0.05%
Since the magnetic circuit is constructed using permanent magnets with a temperature of /°C, a stable magnetic field can be generated. Furthermore, the liquid phase epitaxial magnetic garnet film represented by formula (I) has a temperature coefficient of the absolute value of saturation magnetization of -1 to -1.5 Gauss/°C, and is suitable for temperature compensation with the magnetic circuit. Ori,
Since the temperature coefficient of the absolute value for matching is also small, it is possible to obtain an element that is stable even against rapid temperature changes.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of a magnetostatic wave element of the present invention.

FIG. 2 is a graph showing the relationship between magnet thickness and gap magnetic field in the present invention.

FIG. 3 is a graph showing the relationship between the thickness of the magnet and the temperature coefficient of the absolute value of the gap magnetic field in the present invention.

FIG. 4 is a graph showing the saturation magnetization of the YIG film in the present invention and the temperature coefficient of its absolute value.

FIG. 5 is a graph showing the relationship between the gap length and the gap magnetic field in the embodiment shown in FIG. 1;

FIG. 6 is a graph showing the relationship between the gap length and the temperature coefficient of the absolute value of the gap magnetic field in the embodiment shown in FIG.

FIG. 7 is a sectional view showing a conventional magnetostatic wave element.

[Explanation of symbols]

1 Magnetic garnet film 2 Magnetic circuit 3 York 4 Permanent magnet 5 Coil

Claims (3)

[Claims] 1. Consisting of a magnetic garnet film formed on a non-magnetic substrate, a coil, a yoke, and a permanent magnet with a temperature coefficient of residual magnetic flux density of -0.03 to -0.05 (%/°C), It consists of a magnetic circuit that applies a direct current magnetic field perpendicularly to the magnetic garnet film, and the magnetic garnet film has a temperature coefficient of the absolute value of saturation magnetization of -1 to -1.5 (Gauss).
A magnetostatic wave element characterized in that it is formed of magnetic garnet (s/°C). 2. Formula (I): Y3-zLazFe5-, suitable for forming the magnetic garnet film of claim 1.
tGatO12 t=10
z-0.54 (0.12≦z≦0.14)
A liquid phase epitaxial magnetic garnet film represented by (I). 3. The magnetic garnet film has the formula (I):
Y3-zLazFe5-
tGatO12 t=10
z-0.54 (0.12≦z≦0.14)
2. The magnetostatic wave device according to claim 1, which is a liquid phase epitaxial magnetic garnet film represented by (I).