Electric field effect in EPR and local fields in KTaO3

The splitting ΔHsub(E) of Fe3+ EPR lines in KTaO3 located in an electric field is observed at a temperature of 77 K and in the three-centimeter and eight-millimeter ranges. The angular and electric field dependences of the splitting are studied. A correlation between the angular dependences of ΔHsub(E) and the rate of variation of the resonance field on rotation of the sample in a magnetic field is observed experimentally and derived theoretically. The correlation can be explained by a model in which ion displacements induced by the electric field are taken into account. This permits an estimation of the local field at the oxygen site on basis of the electric field effect in the EPR. The anharmonism constant in the phenomenological Landau theory is derived from the deviation of the electric field dependence of ΔHsub(E) from a linear dependence