Large phase fluctuations near T1 and phase pinning in incommensurate ThBr4: Gd3+ through E.S.R. measurements

Recently, the coexistence of ''normal-like'' and incommensurate 87Rb, N.M.R. lines have been observed in Rb2ZnBr4 below T1, and has been interpreted in terms of a standing wave regime of phase fluctuations between pinning defects. We analyse a similar effect in the E.P.R. spectra of ThBr4:Gd3+. We rule out the possibility of an extrinsic pinning effect due to the E.P.R. probe and we show that inhomogeneous phase fluctuations can account for the observation. A crude application of the model developed by Blinc indicates that the average distance between pinning centres is compatible with their being dislocations. (authors)