Relaxation Effects in the Ferromagnetic Resonance

The spin-lattice relaxation time, $T_1$, has been determined in single crystals of nickel ferrite, by using the ferromagnetic resonance effect at a frequency of 9000 Mc/sec. At high levels of microwave power, the saturation effect is observed both in the resonance absorption and in the component of magnetization along the static field. $T_1$ is computed from these data.

The experimental method is described, and the results presented. Some of the results have not been encountered before in magnetic resonance, and are not predicted by available theories. Because of this, the relaxation time cannot be calculated from the classical theory of the magnetic resonance. By equating the energy absorbed to the energy transferred to the lattice, we obtain a value $T_1\sim 3\times {10}^{-5\mathrm{}}$ sec. This is longer than the decay time observed directly, which is less than a few tenths of a microsecond. The results are compared with available theories of the magnetic resonance and spin-lattice interaction.