Ferromagnetic Resonance in Single Crystals of Cobalt-Substituted Nickel Ferrite

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Abstract
The ferromagnetic resonance linewidth Δ H , the magnetic anisotropy constants K 1 , K 2 and the g -factor are observed at 9.27 GC and in the temperature range from 80°K to 300°K for small spherical single crystal specimens of the composition Co x Ni 1- x Fe 2 O 4 , where, x =0, 0.006, 0.03, 0.06, 0.12. The K 1 , (- K 2 ) and Δ H increase linearly with the increase of the cobalt concentration at a fixed temperature. The ferromagnetic g -factor increases with cobalt content. The contribution of cobalt ion to the anisotropy is found to have nearly the same temperature dependence as that of cobalt ferrite, and the increase of K 1 caused by cobalt ions is well described by Tachiki's theory after putting |αλ|=97 cm -1 and r =0.7. The linewidth at room temperature increases by about 8 Oe for one percent of cobalt ions. The linewidth becomes anisotropic at low temperatures. It is concluded that the contribution of cobalt ions is most pronounced in Fe 3 O 4 , next in MnFe 2 O 4 , and smallest in NiFe 2 O 4 , in agreement with the degree of uniformity of the electric charge distribution on 16d sites.