Ferromagnetic Resonance in Garnet Y₃Fe_5−xCo_x⁄2Ge_x⁄2O₁₂

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The substitution of a small amount of Co²⁺ and Ge⁴⁺ for Fe³⁺ in yttrium iron garnet causes remarkable changes of the magnetic anisotropy constants and ΔH. The magnetic anisotropy constants K₁ and K₂ of Y₃Fe_5−xCo_x⁄2Ge_x⁄2O₁₂ depend strongly on temperature, and K₁ is linear to the concentration of cobalt at a given temperature, where x=0, 0.0042, 0.017, 0.048. The effect of cobalt substitution is similar to the case of magnetite containing cobalt, and can be accounted for by Slonczewski’s theory with the value of the parameter |αλ|=100 cm⁻¹. The line width ΔH increases with the increase in cobalt concentration.