JPS6011449B2 - Garnet magnetic thin film for bubble domain - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a garnet magnetic thin film having tactile magnetic anisotropy useful as a material for bubble domain devices. More specifically, the present invention relates to a garnet magnetic thin film for bubble domains in which minute bubble domains stably exist, bubble domain mobility is high, and temperature characteristics are good. Rare earth orthoferrite was first reported as a magnetic material for bubble domain devices, but this had drawbacks such as the fact that the bit density was not very large due to the large bubble domain law, and poor temperature characteristics. there were. Later, mixed rare-earth iron garnet appeared as a material superior to orthoferrite-based magnetic materials. It has been confirmed that by replacing non-magnetic ions, the saturation magnetization value of the crystal can be adjusted arbitrarily.
As a result, the bubble domain diameter of the garnet-based magnetic material has increased from several microns to several tens of microns, and the bit density has increased considerably, but the domain wall mobility and temperature characteristics are still not sufficient for practical use. Further, in conventional garnet-based magnetic materials, since iron ions were replaced with potassium or aluminum, the Curie temperature decreased significantly, and as a result, the temperature characteristics were not very good. In other words, the temperature characteristics of the magnetic material for bubble domains are the width of the striped domain under zero biased magnetic field, the so-called strip domain width Sw, or the biased magnetic field just before the bubble domain disappears, the so-called extinction. Magnetic field Hcol. It is evaluated by the temperature coefficient of In this respect, the magnetic domain width Sw, extinction magnetic field Hcol. The temperature coefficient was relatively improved, but the Curie temperature was low at around 120 [°C]. Various properties of a magnetic material fluctuate greatly near the Curie temperature, so it is desirable that the Curie temperature be as high as possible relative to the temperature in the device operating state, for example, room temperature. However, it has recently been reported that replacing iron ions with germanium alleviates the drop in Curie temperature and improves temperature characteristics. This can be seen, for example, in the literature Material Research Bulletin, Volume 8, 1973, published by Wang, 1223.
Page 1229. However, the bubble domain diameter of the magnetic material shown in this document is approximately 6
Micron [Buddha? Because they are quite large, ``there is a problem in terms of bit density. Therefore, in order to further increase the bit density, we support micro baffles, so-called submicron bubbles, with a bubble diameter of around 1 micron or less. As a crystal for submicron bubbles, mixed rare garnet ((RR)3(FeGa)50,2) is generally a candidate. This crystal has a t-bubble diameter of submicron. Although it has a large anisotropy constant ku, which is necessary for achieving high bubble mobility, it has poor temperature characteristics and the damping of rare ions has a large effect, so it has drawbacks such that it is difficult to expect a very large value for bubble mobility. The purpose of the present invention is to obtain a crystal that does not have the above-mentioned drawbacks, that is, to obtain a crystal in which submicron bubbles stably exist, a crystal with large bubble domain mobility, and which also has good temperature characteristics and a high Curie point. An object of the present invention is to obtain a garnet magnetic thin film for bubble domains grown on a gadolinium-gallium-garnet substrate by a liquid phase epitaxial growth method, and to obtain a garnet magnetic thin film for bubble domains grown on a gadolinium-gallium-garnet substrate by a liquid phase epitaxial growth method. A garnet magnetic thin film for bubble domains, which has the kaiy012 magnetochemical formula and has the above x and y values in the range of 0.23 x mi 0.5 and 0.5 mm y mi 0.85, respectively. The garnet magnetic thin film according to the present invention will be described in detail below. Garnet Y3Fe50,2 (YIG) is a fibrillar magnetic material with a saturation magnetization of 4 mms and 1750 Gauss.
ss]. The necessary conditions for a crystal for bubbles are ``a crystal with one-tree anisotropy, an anisotropic magnetic field Hk due to uniaxial anisotropy, and a saturation magnetization of 4
Ms=q(qualityfac
The value of r) is 1 or more. In order to increase uniaxial anisotropy, yttrium Y30 is generally replaced with rare ions, and in order to reduce 4Ms from the relationship between bubble mobility and the above-mentioned quality factor q, iron It is known to replace a part of the ion Fe30 with a pair of nonmagnetic ions such as gallium Ga30, aluminum mountain 30, or calcium Ca20 and germanium C40. However, each rare ion has its own damping constant, and even those with large or small constants are replaced with yttrium Y30 in large quantities.
The damping constant becomes larger and as a result acts to suppress the bubble as it moves. In other words, the mobility of the bubble becomes smaller. In addition, in order to lower the saturation magnetization 4Ms, a part of the iron ion Fe30 is replaced with gallium Ga30,
Garnet substituted with aluminum mountain 30 has poor temperature characteristics. A possible garnet with good temperature characteristics is one in which part of the iron ion Fe30 is replaced by a pair of calcium Ca20-H40, and this was used. This is reflected in the patent application filed in 1972-12 by the present applicant.
6131 and Japanese Patent Application No. 126134/1984. Please refer to these for details. First of all, the conditions for a crystal for submicron bubbles are that the characteristic length of the crystal is 1.
It is necessary to make it approximately 0.1 micron [mountain surface] or less, and for this purpose, considering stability and assuming that the saturation magnetization is 4 mMs to 500 Gauss [Ga vessel s] and the quality factor qmi2, the anisotropic The sexual constant ku is approximately 2.0×
It must take a value of 1 pi [erg/] or more. Anisotropy constant ku', calcium Ca-germanium Q
Garnet (e.g. YCaEuYbGeI) using a pair of
For G (YCaEuTm, IG, etc.), it is less than 2.0 The following three points need to be taken into consideration when selecting: 1. A combination of rare ions and rare earth ions with large anisotropy. 2. A combination with a small damping constant. 3. Match the lattice constant with the 0GG (Gd30a20,2) substrate. Considering these three points, we used Sm30, which is thought to produce the greatest anisotropy among rare ions, and furthermore, Sm30 has a lattice that is smaller than that of gadolinium-gallium-garnet (Q°C), which is used as a substrate crystal. Since the constant is large and the damping constant is not small, Tm30, which has a small damping constant and is nonmagnetic and has a lattice constant smaller than that of the fitted substrate, is used as the rare earth ion used in combination with this.The composition ratio of these is GGG. We decided that Sm:Tm = 2:5 from the matching with the lattice constant of the substrate.A small damping constant means that the spin reversal speed in the crystal is small, and the domain wall mobility is large. A fast-speed bubble device can be obtained.Garnet magnetic thin film Y3 according to the present invention
-yraxCaySmXTmcloudXFe5-yQy. The range of the composition of X that becomes 2 is from 0.2 to 0.5, and y
The composition range is from 0.5 to 0.85. The lower limit value of x is 0.2, which is limited from the viewpoint of bubble stability.
Below this, bubbles cannot exist stably, and when applied to devices, the credit level decreases, which is undesirable. On the other hand, the upper limit value of x of 0.5 is determined from the viewpoint of wall mobility, and if it exceeds this value, the bubble device cannot be put to practical use in terms of speed.
Further, if the lower limit value of y is less than 0.5, the spontaneous magnetization 4mMs increases and the bubble diameter becomes further smaller, but the quality factor q becomes around 1, which is undesirable in terms of stability. On the other hand, if the upper limit value of y is 0.85 or more, the spontaneous magnetization of 4mMs becomes small, and the bubble diameter becomes about 3 microns (r), which does not meet the current target in terms of bit density. Next, examples developed in accordance with the present invention will be presented and explained while evaluating the characteristics of the magnetic thin film according to the present invention based on experimental data. Example Y Public Fake - Wife XC ~ - Technique Sm XTm Heat x Fe4.25Geo. For the composition of method ○, 2, the value of x is 0.
Five types, 1, 0.2, 0.30, and 40.5, were selected and each was grown on the {111} plane of the substrate crystal Gb3Ga50,2 by liquid phase growth. Table 1 shows the melt compositions used to grow these samples, and Table 2 shows the characteristics of each sample when the values of the composition x of rare ions were set to these five types. Table 1 2 Each oxide shown in Figure 1 was mixed and placed in a platinum crucible, and the temperature of the crucible was set to 1100.

After holding at [00] for 2 to 3 hours, the temperature was lowered to about 890 to 0], and epitaxial growth was performed on the substrate crystal in a supersaturated state. As can be seen from Table 2, the width of the magnetic domain (strip domain) Sw' of each sample was around 1 micron, which fully achieved the initial goal.Therefore, the bubble diameter was also 1 micron. When applied to devices, it is desirable that the relationship between the diameter d of the pulley and the characteristic length 1 be d = 8 to 10, but all of these samples satisfy this condition. As mentioned above, the larger the ratio q of the anisotropic magnetic field Hk to the saturation magnetization 4mMs, the more stable bubbles exist, but conversely the domain wall mobility decreases. From this point of view, x = 0. It can be seen that the sample with x = 0.1 is inferior to other samples in terms of bubble stability. Therefore, it is not suitable for devices that require high reliability. Conversely, the sample with x = 0.5 has the highest q. Although it is large and has sufficient stability, the domain wall mobility is low, so it is not suitable for devices that require high speed. Figure 1 shows the change in the domain wall mobility rd when the value of x is changed. The horizontal axis is the magnetic field gradient △day (∊), and the vertical axis is the bubble velocity ○ (inhibition/sec
) are shown respectively. Note that the figure shows plots of experimental data when using samples with x=0.2, 0.3, and 0.4. As is clear from this figure, as the value of x increases, the domain wall mobility peak d decreases. Second
The figure is a graph showing the relationship between the composition x of rare ions and the anisotropy constant ku. In addition, Fig. 3 is a diagram for explaining the temperature characteristics when the value of x is changed, and Fig. 3 a shows the extinction magnetic field Hcol of the bubble.
．． In addition, figure b shows the temperature characteristics when the vertical axis is the magnetic domain width Sw.The horizontal axes of figure a and b are temperature, and the value of x is 0.2,
It is a graph created based on experimental data investigated on samples set to 0.3 and 0.4. From these graphs, it can be seen that the grown samples have good temperature characteristics. In particular, it can be seen that the temperature dependence of the magnetic domain width Sw shown in FIG. Table 3 is the third
This is a table summarizing the temperature coefficient and Curie temperature of each graph shown in the figure. Table 3 As is clear from this table, the temperature coefficient of the bubble extinguishing magnetic field in Figure 3a is -0.24%/℃ for the sample with x=0.2.
], -0.19 [%/qC] for the sample with x=0.3, x=
The temperature coefficient of the magnetic domain width shown in Figure 3b is as small as -0.15 [%/qC] for the 0-4 sample.
．． The sample with x=0.4 has a value of 100.01 [%/°C], and the sample with x=0.4 has a value of -0.01 [%/°C], which is very small. These values are very small compared to conventional materials. However, these temperature coefficients are in the temperature range from room temperature to 100 [OC]. Furthermore, the Curie points of each of the grown samples were all 210[00] or higher, which is considerably higher than that of conventional crystals. Therefore, when a bubble device is operated at room temperature, for example, variations in various properties of the magnetic material are extremely small, and very stable operation can be achieved. Although the samples with x = 0.5 are not shown in Figures 1 and 3, the temperature characteristics and Curie point are also the characteristics of the samples with x = 0.2, 0.3, 0.4. A system that estimates based on the trends of the results is sufficient for practical use. As explained above, the garnet magnetic thin film according to the present invention can greatly reduce the bubble diameter by 4 mm and improve the bit density. In addition, since it has good temperature characteristics and a high Curie point, thermal malfunctions can be minimized. Furthermore, the wall mobility is relatively high compared to conventional ones, making it fully suitable for increasing the speed of bubble devices. In the above embodiment, only the case where y=0.75 was explained, but a stable and even smaller bubble crystal can be realized by decreasing the value of y and increasing the rare ± neck ion ratio x. .

[Brief explanation of drawings]

Figures 1 to 3 are diagrams for explaining the characteristics of the magnetic thin film according to the present invention, and Figure 1 is a diagram showing the domain wall mobility of each sample when the value of the rare earth ion composition ratio x is changed. , Figure 2 shows the relationship between the formation of rare ions and the anisotropy constant, Figure 3
The figure shows the temperature characteristics of each test. O diagram B Otsu diagram O 3 diagram

Claims (1)

[Claims] 1 In a garnet magnetic thin film for bubble domains grown on a gadolinium-gallium-garnet substrate by liquid phase epitaxial growth method, Y_3-y-7/
2x CaySmxTm5/2x Fe_5-y Ge
It is expressed by the chemical formula yO_1_2, and the values of x and y are 0.2≦x≦0.5 and 0.5≦y≦0.85, respectively.
A garnet magnetic thin film for bubble domains, characterized in that it is in the range of .