Ferromagnetic relaxation in yttrium-iron garnet and the relation to applications

Ferromagnetic relaxation measurements in single-crystal yttrium-iron garnet (YIG) are given over the range of 4.2° to 300°K. This is a report on the present status of YIG in which care has been taken to remove the extraneous rare-earth impurity ions and ferrous impurity ions. The measurements are reported in terms of the linewidth, ¿Hk¿0, of long-wavelength spin waves, which has been found to be approximately equal to the intrinsic linewidth of the uniform precession. ¿Hk¿0 is related to the spin lattice relaxation time by the following: ¿Hk¿0 ¿ 1/¿T10. The values of ¿Hk¿0 were obtained using the parallel pumping technique, in which spin waves of known wavelength are generated at one-half the microwave frequency. A discussion is given of the usefulness of YIG in low-frequency microwave devices, low-temperature microwave power limiters and the Denton ferromagnetic amplifier.