JPS6117065B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a garnet film for magnetic bubble devices in which hard bubbles are not present. It is well known that a magnetic garnet thin film epitaxially grown on a substrate of non-magnetic gallium garnet, such as Cd ₃ Ga ₅ O ₁₂ , is used as a magnetic film for a magnetic bubble device. Conventional
Substrates such as Gd ₃ Ga ₅ O ₁₂ are processed to have a (111) plane, and because magnetic bubbles stably exist in the epitaxial magnetic garnet film grown on it, the film It must have uniaxial magnetic anisotropy such that the direction perpendicular to the surface, that is, the [111] direction, is the axis of easy magnetization.
However, in a garnet film having such uniaxial magnetic anisotropy, bubbles called abnormal bubbles or hard bubbles are also generated in addition to normal bubbles. It is known that hard bubbles have a higher bubble extinguishing magnetic field than normal bubbles, are transferred in a direction oblique to the magnetic field gradient, and have a lower domain wall movement speed. This is because, unlike normal bubbles, hard bubbles have a complex domain wall structure. Needless to say, if such hard bubbles exist during operation as a magnetic bubble element, their abnormal dynamic characteristics will cause malfunctions, which is undesirable. Several methods are known for suppressing such hard bubbles, for example,
Volume ``Magnetic Bubble'' (edited by Shuichi Iida et al., Maruzen) P123 includes (1) ion implantation method, (2) permalloy coating method, (3)
YGdIG coating method, (4) YIG coating method, (5) double film formation method, (6) high temperature annealing method in inert gas, (7) method of reducing q value, (8) In-plane bubble layer A method of imparting two-fold symmetrical magnetic anisotropy to is described. However, in (1) to (6) above, a 90° or 180° domain wall is formed between the bubble layer and the cap layer, and a cap layer must be additionally formed in addition to the bubble layer that holds the magnetic bubbles. This requires an extra process. (7) is a method in which hard bubbles are suppressed using a single magnetic film, but the fact that the q value is low means that magnetic bubbles are generated naturally without need due to slight fluctuations in the magnetic field. The q value must be high from the viewpoint of reliability as a magnetic bubble element. From this point of view, the q value is required to be 2 or more. In (8), the substrate surface is tilted from (111) so that the axis of easy magnetization is no longer perpendicular to the film surface, but in this method, due to the in-plane magnetic field effect, the bias magnetic field where the magnetic bubbles stably exist is The upper and lower limits should shift depending on the direction of the in-plane magnetic field, and this method is not actually used. The present invention eliminates the need for extra steps such as those in (1) to (6) above, eliminates the drawbacks of (7) and (8), and provides a magnetic bubble element for magnetic bubble elements free of hard bubbles. The purpose is to provide a membrane. The present inventor grew a magnetic garnet film on a gallium garnet substrate with a (110) plane, satisfying q1=Ku/2πMs ² >2, and further set q2=Ki/2πMs ² >5. It has therefore been found that a stable magnetic film for a magnetic bubble element can be obtained in which hard bubbles are not generated and magnetic bubbles are not generated or extinguished unnecessarily.
(110) By imparting large strain-induced anisotropy or special growth-induced anisotropy to the garnet film grown on the substrate, the axis of easy magnetization is perpendicular to the film surface, and It is known that magnetic anisotropy with 2-fold symmetry can also be provided. Examples of such materials can be found in Applied Physics Letters Vol.
Volume 29, No. 12, page 815 (1976) Also page 817, IEEE Trans.
Magneties) Vol. 13, No. 5, page 1087 (1977), etc. This kind of anisotropy is called orthorombic magnetic anisotropy, and the magnetic anisotropy energy of a material with orthorombic magnetic anisotropy is determined by Ku, which represents the energy difference between the easy axis of magnetization and the intermediate axis, and the in-plane magnetization. Using Ki, which represents the energy difference between the difficult axis and the intermediate axis, it can be expressed as E=(Ku+Kisin ² φ) sin ² Θ. The present inventor has proposed (110) plane Gd ₃ Ga ₅ C ₁₂ and Nd ₃ Ga ₅ O ₁₂
Magnetic garnet films with various types of orthorombic magnetic anisotropy were grown on substrates, and the presence or absence of hard bubbles and the value of the ratio of the Ku and Ki values of the film divided by the demagnetizing field energy 2πMs ² , That is,
The relationships between q1=Ku/2πMs ² and q2=|Ki|/2πMs ² were investigated in detail. Since there is no in-plane anisotropy in the film on the (111) substrate, it can be defined that q2 = 0. (111) Hard bubbles occur in the film on the substrate when q1>2, but on the other hand, if the film on the (110) substrate has orthorombic magnetic anisotropy with q2≠0, then q2>5. satisfies q1>2, which is required for the stable existence of bubble magnetic domains, and
We also discovered that it is possible to reliably prevent the existence of hard bubbles. The present invention will be explained below with reference to Examples. Table 1 shows the type of epitaxial magnetic garnet film, substrate crystal and plane orientation, saturation magnetization (4πMs), q1
value, q2 value, and presence or absence of hard bubbles. The figure shows q1 and q2 of samples #1 to #12 in Table 1.
In this plot, × indicates no hard bubble, and ○ indicates presence of hard bubble. As is well known, the presence or absence of hard bubbles was determined by utilizing the fact that when hard bubbles exist, the bubble extinguishing magnetic field spreads. From Table 1 and the figure, setting q2 > 5 is required for the stable existence of bubble magnetic domains.
It can be seen that it is possible to provide a garnet film for magnetic bubble elements that satisfies q1>2 and is free of hard bubbles. Regarding each magnetic garnet film shown in Table 1,
The respective melt compositions and growth conditions are shown in Table 2.

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[Table] As explained above. By using a magnetic garnet film on a (110) substrate with q1 > 2 and q2 > 5, no extra process is required to suppress hard bubbles, and a stable magnetic garnet film can be used as a magnetic bubble element. A membrane is obtained.

[Brief explanation of the drawing]

The figure shows the presence or absence of hard bubbles using q1 and q2 as parameters, and the 〇 and × marks indicate the presence or absence of hard bubbles, respectively.

Claims (1)

[Claims] 1. A garnet substrate, an axis of easy magnetization epitaxially grown on the (110) plane of this substrate, which is perpendicular to the film plane and has magnetic anisotropy within the film plane, and q1=Ku /2πMs ² >2 and q2=Ki/2πMs
A garnet film for a magnetic bubble element, characterized in that it is made of a magnetic garnet film in which ² >5.