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, $\mathrm{S}\mathrm{B}\mathrm{N}:\mathrm{C}\mathrm{e}$, close to its phase transition temperature $T_c\approx 317\mathrm{K}$. A gradual increase of the critical exponent from $\beta \approx 0.13$ to $\beta \approx 0.30$ 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.