Ferromagnetic Resonance of Single-Domain Particles

The ferromagnetic-resonance spectra of powders containing single-domain particles have been studied experimentally and theoretically. The theory is based on the Stoner-Wohlfarth model. The line shapes were calculated with the aid of a high-speed digital computer. Measurements were made on $\gamma$-${\mathrm{Fe}}_2$ ${\mathrm{O}}_3$ powders, both with and without an applied steady magnetic field. For zero applied steady field, the theoretical line shapes agree well with the experimental ones provided the particle shape distribution, the crystalline anisotropy, and the particle interactions are taken into account. With an applied field, the theoretical curves with only the shape distribution considered do not agree with the theoretical ones. It is found that the anisotropy constant $K_1$ and the relaxation time $\tau$ of $\gamma$-${\mathrm{Fe}}_2$ ${\mathrm{O}}_3$ are approximately -2.5×${10}^5$ ergs/${\mathrm{cm}}^3$ and 2.0×${10}^{-10\mathrm{}}$ sec, respectively.