Concentration dependence of the random field crossover scaling in FexZn1−xF2

Abstract

The proportionality between the field-induced shift ΔTc(H) of the transition temperature Tc(H) and the root-mean-square (rms) random-field hRF was studied over a wide range of concentration (0.31≤x≤0.84) in the nearly ideal random-field Ising model (RFIM) system FexZn1−xF2. Tc(H) was determined experimentally from the optical birefringence Δn, for which d(Δn)/dT exhibits a peak proportional to the magnetic specific heat. For all x studied, Tc(H) was found to shift from the H=0 transition at TN as ΔTc(H)ΔTc(H)= cTN h2/φRF as predicted, with φ=1.42±0.03 the universal random exchange to RFIM crossover exponent, after a mean-field correction bH2. The nonuniversal quantity c was found to be of order unity as expected, but slightly x dependent.