Spin Resonance of Transition Metal Ions in Corundum

Abstract

The results of electron spin resonance experiments on a series of transition metal ions in single crystals of corundum are reviewed and interpreted in terms of crystal field theory emphasizing three topics: (1) The strength of the cubic crystal field, (2) the axial field as an indicator of position of the impurity ion, and (3) Jahn‐Teller effects in the ground state. The 4d and 5d ions which were examined, i.e., Ru³⁺, Rh³⁺, and Ir³⁺ are found to be strong crystal field cases. In addition, the increased charge of Ni³⁺(3d⁷) is shown to be sufficient to drive it to a strong crystal field case (t₂⁶e) with S = ½ compared to Co²⁺ (3d⁷) which is t₂⁵e³ with S = $\frac{3}{2}$ . The parameter v which measures the trigonal field potential, was found to be +850 cm⁻¹ in Ru³⁺ in good agreement with other ions such as Co²⁺ and V³⁺ whose cubic field ground states are also orbitally degenerate. In contrast, the determination of v from ESR data on ions with singlet ground states such as Cu³⁺ and Ni²⁺ is regarded as less reliable. The Jahn‐Teller effect was observed for Pt⁺ (or Pt³⁺), Ni³⁺, and Cu²⁺.