Magnetic Behavior of Cobalt in Garnets. II. Magnetocrystalline Anisotropy and Ferrimagnetic Resonance of Cobalt-Doped Yttrium Iron Garnet

Measurements on single crystals of yttrium iron garnet (YIG) doped with cobalt, some counterdoped with silicon or calcium, show that the magnetocrystalline anisotropy is dominated by octahedral ${\mathrm{Co}}^{2+}$ and tetrahedral ${\mathrm{Co}}^{3+}$. Both are present in uncompensated material. We calculate the single-ion anisotropy of ions of the ${\mathrm{}\left(3d\right)\mathrm{}}^n$ series ($n=4-9\mathrm{}$), incorporated into the various sites of YIG. We find qualitative agreement with experiment in the case of cobalt. A preliminary study of ferrimagnetic resonance in uncompensated cobalt-doped crystals shows that octahedral ${\mathrm{Co}}^{2+}$ does not make the large contribution to the linewidth at 0°K predicted by Haas and Callen, and indicates that either octahedral ${\mathrm{Co}}^{2+}$ or tetrahedral ${\mathrm{Co}}^{3+}$ relaxes through an excited state 130 ${\mathrm{cm}}^{-1\mathrm{}}$ above the ground state.