Paramagnetic-resonance studies of local fluctuations in SrTiO3 above Tc

Abstract

Detailed studies on electron paramagnetic resonance (EPR) of the Fe3+-V0 center in a monodomain single crystal of SrTiO3, have been made for Tc<T<295 K. By adjusting the direction of the applied magnetic field, the sensitivity of the EPR frequency to the local rotation angles of the oxygen octahedra can be varied. A comprehensive theoretical analysis of this technique was carried out, making it possible to separate the secular, nonsecular, and background effects. We then showed from the angular dependence of the observed secular linewidth, that the slow-motion regime is obtained throughout the critical region Tc<T<Tc+11 K, i.e., the local fluctuations are static on the time scale of the EPR relaxation itself. The EPR line shapes in this region then provide a direct measure of the distribution of local rotation angles. An upper limit of 6 MHz is placed upon the characteristic frequency of the local-rotation fluctuations in this region. The characteristic collective-mode relaxation rate, i.e., the "central-peak" width, should be about an order of magnitude narrower. © 1980 The American Physical Society.