Change from 3D-Ising to random field-Ising-model criticality in a uniaxial relaxor ferroelectric

Abstract

Pyroelectric measurements of polarization have been used to determine the temperature dependence of the polarization in strontium barium niobate, SBN:Ce, close to its phase transition temperature T(c)approximate to317 K. A gradual increase of the critical exponent from betaapproximate to0.13 to betaapproximate to0.30 is observed when decreasing the initial polarization from 100% to 0.8% of the saturation value. A change from three-dimensional random-field Ising to pure Ising model behavior is conjectured and explained by a gradual compensation of quenched random electric fields by those emerging from charged fractal nanodomain walls.