The properties of (3d)4ions in corundum. I. APR spectra and their interpretation

Abstract

Measurements have been made of the acoustic paramagnetic resonance spectra of both Cr²⁺ and Mn³⁺ in Al₂O₃ at frequencies between 8.4 and 9.5 GHz. Results have been obtained as the direction of the magnetic field H is verified in the ac plane, the bc plane and in a cone around the c axis. Two types of lines are in evidence: type 1 lines have an edge and type 2 lines a peak. The shapes are explained by assuming that random internal strains and electric fields of E type symmetry exist in the crystal. The variations of the positions of the peak or edge as H is varied are readily explained. This analysis shows that (3d)⁴ ions in Al₂O₃ are at a site which has predominantly trigonal symmetry and that the superimposed random tetragonal components are small.