Magnetic Spectra of Manganese Ferrites

Abstract

The complex initial permeability of a series of polycrystalline manganese-rich manganese ferrites (${\mathrm{Mn}}_{1+x}{\mathrm{Fe}}_{2-x}{\mathrm{O}}_4$) has been measured between 20 Mc/sec and 2000 Mc/sec. Three resonances are detected; the two lower-frequency resonances, which occur below 200 Mc/sec, are associated with domain wall motion. The higher-frequency resonance, which varies between 300 and 600 Mc/sec depending on the composition, allows the calculation of an effective polycrystalline anisotropy constant, $K_e$. Microwave resonance measurements on single crystals of the same composition give the real anisotropy constant $K_1$. Comparison of these two experiments show that $K_e\approx 2K_1$. Measurement of the magnetic moment indicates that in these compounds the ${\mathrm{Mn}}^{3+}$ ion assumes a value of approximately two Bohr magnetons instead of the expected four Bohr magnetons.