Ferromagnetic Resonance in Ruthenium-Doped Gadolinium Iron Garnet

Ferromagnetic-resonance measurements on single crystals of gadolinium iron garnet doped with ruthenium were carried out at 9.25 GHz in the temperature range 4.2-500 ^∘{}K. The single-ion model is used to calculate the anisotropy contributions ΔK₁ and ΔK₂ and the field for ferromagnetic resonance. By fitting the theory to the experimental anisotropy data one finds gHₑ=1.2×10⁷ Oe and vξ=-0.4, where g, Hₑ, v, and ξ are the g factor, the exchange field, the one-electron trigonal-field parameter, and the one-electron spin-orbit-coupling parameter, respectively. The linewidth could be interpreted in terms of the longitudinal-relaxation model assigning a short relaxation time of τ=3.3×10^-12 sec to the Ru³⁺ ions.