Frequency-Dependent Anisotropy in Si- and Ca-Doped YIG and LuIG

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Abstract
The magnetic anisotropy of small spherical samples of Si‐ and Ca‐doped single‐crystal yttrium and lutetium iron garnets has been studied at 10 and 25 kMc/sec over the temperature range from 4.2° to 300°K. The experimental results have been compared with similar data from static torque measurements. There is a considerable difference between the microwave and static magnetic anisotropy in doped garnets, while for pure garnets the agreement between the microwave and static data is very good. In particular, the microwave first‐order anisotropy constant in Si‐ and Ca‐doped garnets is less negative than the static anisotropy constant, which is independent of doping, and the difference between the two types of measurements is linearly proportional to the doping density. In Ca‐doped garnets the microwave anisotropy constant becomes zero at about 5.5% doping density, and for larger Ca concentrations changes sign and becomes positive. The same effect, although of lesser magnitude, is observed in Si‐doped garnets. The frequency dependence of the microwave anisotropy is confirmed by measurements at two different wavelengths. As expected, the deviation of the microwave anisotropy constant from the static one is larger at 25 than at 10 kMc/sec.