Electron Spin Resonance ofRu3+in Yttrium Gallium Garnet and Yttrium Aluminum Garnet

Abstract

Electron-spin-resonance data at 4.2\ifmmode^\circ\else\textdegree\fi{}K have been obtained for ${\mathrm{Ru}}^{3+}$ in the octahedral sites of yttrium gallium garnet (YGaG) and yttrium aluminum garnet (YAlG). The experimental values are ${g}_{\ensuremath{\parallel}}=3.113\ifmmode\pm\else\textpm\fi{}0.003$, ${g}_{\ensuremath{\perp}}=1.148\ifmmode\pm\else\textpm\fi{}0.002$, ${A}_{\ensuremath{\parallel}}=63.3\ifmmode\pm\else\textpm\fi{}0.8$, and ${A}_{\ensuremath{\perp}}=38\ifmmode\pm\else\textpm\fi{}5$ for YGaG, and ${g}_{\ensuremath{\parallel}}=2.88\ifmmode\pm\else\textpm\fi{}0.02$, ${g}_{\ensuremath{\perp}}=1.300\ifmmode\pm\else\textpm\fi{}0.004$, ${A}_{\ensuremath{\parallel}}=56.4\ifmmode\pm\else\textpm\fi{}0.7$, and ${A}_{\ensuremath{\perp}}=41\ifmmode\pm\else\textpm\fi{}2$ for YAlG, where the hyperfine constants are in units of ${10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{\ensuremath{-}1}$. From an analysis of the $g$ values of the low-spin $4{d}^{5}$ system, one obtains $\frac{v}{\ensuremath{\zeta}}=\ensuremath{-}1.06$ in YGaG and -0.78 in YAlG, where $v$ is the trigonal field parameter and $\ensuremath{\zeta}$ is the spin-orbit coupling constant. Thus the trigonal field in the garnets is negative and opposite in sign to the trigonal field of the octahedral site in corundum. The core polarization field obtained from the hyperfine constants is -220 kG/(unpaired spin) in YGaG and -250 kG/(unpaired spin) in YAlG, which is about twice the approximately constant value of -125 kG/spin found in the $3d$ series.