Exchange stiffness coefficients of YIG:CaGe and YIG:LuSc from 30 to 300 K

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Abstract
The exchange stiffness coefficients A of tetrahedrally substituted YIG:CaGe and octahedrally substituted YIG:LuSc have been determined over the temperature range of 30 to 300 K. The magnetization M of each sample was measured range of 30 to 300 K. The magnetization M of each sample was measured with a vibrating sample magnetometer. The spin wave dispersion coefficient 2A/M was measured using microwave resonance techniques. Values of A were determined as a function of substitution level, the microscopic site of the substitution, and temperature. The results of this study indicate that the Kirkpatrick and Harris percolation model provides a close agreement with the experimental data obtained in this work. The most significant result of this work is represented by a plot of the room temperature values A versus the Curie temperature of each sample. Data for both systems studied here fall on the same curve. It appears that this general curve will yield values of A for a wide range of substituted garnets. Available data on magnetic garnet bubble device materials has verified the predictability of this general curve.