Electron paramagnetic resonance and magnetic circular dichroism double resonance of the V− center in MgO

Abstract

This work presents the results of an experimental and semi-theoretical investigation of the V − paramagnetic colour center in MgO. The magneto-optical properties of this center were investigated by using a combined electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) double resonance technique, at temperatures down to 1·6°K. This allows one to correlate positively the 2·3 eV optical absorption band and the axially symmetric spin resonance spectrum. The MCD spectrum is asymmetric, and appears to be a combination of absorptive and derivative like components. The spectrum follows a spin-1/2 Brillouin function, in H/T, and is quenched by high microwave power at both the parallel and perpendicular g-values. To account for the asymmetric shape of the MCD, an analysis is made of previous arguments which were based on a model in which the hole is localized on a single O 2− ion, next to the vacancy. It is found that this description is inconsistent with the experimental evidence presented, and consequently a delocalized model is proposed, through the use of molecular orbital (MO) theory. Considering a MO scheme which has an A 1 ground state and a set of E-like excited states, it is possible to explain qualitatively many of the magneto-optical characteristics which were experimentally observed.