Electron-Spin-Resonance Absorption Spectrum of Platinum in Yttrium Aluminum Garnet

An electron-spin-resonance absorption spectrum taken at 3-cm wavelength and attributed to trivalent platinum ($5d^7,t^{6}e$) at octahedral sites in yttrium aluminum garnet has been observed at temperatures below 120°K. The spectrum is described by $S=\frac{1}{2}$ and $\mathrm{I}=\frac{1}{2}$ (due to the 34% abundant ${}_{}{}^{195}{}_{}{}^{}\mathrm{Pt}$). There are 24 magnetically inequivalent orientations of the platinum ion per unit cell arising from what is believed to be static Jahn-Teller distortions at each of the eight inequivalent octahedral sites. The $g$ and $A$ tensors are orthorhombic with principal components $g_i=1.962\mathrm{}$, $g_j=2.361\mathrm{}$, $g_k=2.424\mathrm{}$ and $A_l=99\mathrm{} \mathrm{Oe}$, $A_m=88\mathrm{} \mathrm{Oe}$, and $A_n=30\mathrm{} \mathrm{Oe}$. The two tensors are not diagonal in the same coordinate system and their orientations with respect to the garnet cubic directions is discussed.