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 ${\mathrm{Y}}_{3-x}{A}_x{\mathrm{Fe}}_{5-y-z}{\mathrm{Ir}}_y{B}_z{\mathrm{O}}_{12-\delta }{\mathrm{F}}_{\delta }$ ($A={\mathrm{Ca}}^{+2\mathrm{}},{\mathrm{Pb}}^{2+} \mathrm{and} B={\mathrm{Fe}}^{2+},{\mathrm{Si}}^{4+},{\mathrm{Zn}}^{2+}$) 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 $\Delta K_1$ and $\Delta K_2$ caused by the low-spin $5d^5$ ${\mathrm{lr}}^{4+}$ ions are positive with $\Delta K_2>>\Delta K_1$ and the magnetostriction contributions $\Delta {\lambda }_{100}$ and $\Delta {\lambda }_{111}$ are negative with $\left|\Delta {\lambda }_{100}\right|\gg \Delta {\lambda }_{111}$. 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 $T=370\mathrm{}$ K could be qualitatively interpreted by the longitudinal relaxation model assigning a relaxation time of ${10}^{-11\mathrm{}}$ sec to the ${\mathrm{lr}}^{4+}$ ions.