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 = 32. 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+.