Paramagnetic Resonance Spectra of Chromium and Manganese in the Spinel Structure

The paramagnetic resonance spectrum of Cr³⁺ was measured on the single crystal of ruby spinel MgAl₂{O}₄$ at the wavelengths of 3 cm, 1.2 cm, and 8.6 mm. The spectrum confirms that ${Cr}³⁺$ is at a $B$ site and can be described with an axial spin Hamiltonian $S=3/2$, $2D=0.990±{}0.005$ ${cm}^{{-}1}$, ${g}II=1.986±{}0.001$, ${g}_{{⊥}}=1.989±{}0.002$.The paramagnetic resonance spectrum of ${Mn}²⁺$ was measured on the single crystal of Zn${Al}₂O₄ at 3 cm. The spectrum consists of six nearly isotropic lines with A=74.9±0.5×10^-4 cm^-1, g=2.000₂±0.001. The cubic or axial splitting was less than 8×{}10^-4 cm^-1. The spectrum is indicative that Mn²⁺ is located at an A site.