Large Random-Field Behavior above the Vacancy Percolation Concentration Threshold: Fe_0.84Zn_0.16F₂

Abstract

High-field magnetization measurements, with H ≤ 20 T, yield the random-field Ising model (RFIM) specific heat behavior near the H-T phase boundary in Fe_0.84Zn_0.16F₂. This sample, with x greater than the magnetic vacancy percolation threshold, x_v=0.754, is in the concentration range that shows equilibrium neutron scattering line shapes at low temperature and |q|>0, unlike samples for which x<x_v. The temperature derivative of the uniform magnetization shows the expected low-field random-field Ising scaling behavior for H ≤ 18 T. At H=20 T, however, the peak temperature and amplitude are significantly suppressed, indicating a high-field RFIM region of the H-T phase diagram.