Some critical phenomena near ferroelectric phase transition in Li2Ge7O15 crystals

The anomalous ESR line width broadening has been investigated near ferroele ctric phase transition point of lithium heptagermanate Li2Ge7O15 (LGO) dope d with Mn2+ ions. Temperature and orientational dependencies of ESR spectra show that line width broadening is contributed by low frequency (omega < 1 0(7) Hz) order parameter fluctuations associated with central peak in the e xcitation spectrum of LGO. The critical exponent of correlation length nu a pproximate to 0.63 derived from the ESR line width measurements is consiste nt with Izing model. It is assumed that long range dipole-dipole interactio ns become noticeable in the narrow vicinity near transition point.