Anisotropy and Magnetostriction of Iridium-Substituted Yttrium Iron Garnet

The anisotropy, magnetostriction, and linewidth of iridium-substituted yttrium iron garnet single crystals of the composition Y_3-xAₓFe_5-y-zIryBzO_12-δF_δ (A=Ca⁺²,Pb²⁺ and B=Fe²⁺,Si⁴⁺,Zn²⁺) have been investigated by means of ferromagnetic resonance. Chemical-analysis data of Ir, Zn, Ca and of the impurities Pb, Si, and F are given for all crystals. The anisotropy and magnetostriction measurements were carried out at 9.15 GHz in the temperature range 4.2-500 K. The anisotropy contributions ΔK₁ and ΔK₂ caused by the low-spin 5d⁵ lr⁴⁺ ions are positive with ΔK₂>>ΔK₁ and the magnetostriction contributions Δλ₁₀₀ and Δλ₁₁₁ are negative with |Δλ₁₀₀|Δλ₁₁₁. The temperature dependence of both the anisotropy and magnetostriction is compared with calculations performed in the framework of the single-ion theory. The resonance linewidth showing a maximum at $T=370$ K could be qualitatively interpreted by the longitudinal relaxation model assigning a relaxation time of 10^-11 sec to the lr⁴⁺ ions.