Influence of the coupling in quadrature of two displacement modes and of the phase of the modulation wave on e.s.r. line shapes and relaxation, in the incommensurate phase of ThBr4 : Gd3+

Abstract

By varying the magnetic field orientation we obtain several types of E.S.R. line shapes in the incommensurate phase of ThBr4 : Gd3+. They depend on the relative importance and on the phase of linear and quadratic contributions to the local line shifts due to two displacement modes in quadrature. Moreover, phase fluctuations may have drastic effects by averaging the incommensurate-line or by giving rise to a local phase-dependent relaxation time T1. Amplitude fluctuations may also contribute to a local phase-dependent line width.