Random-Field Effects on Critical Behavior of Diluted Ising Antiferromagnets

Abstract

Random-field effects have been studied, using linear birefringence, in the random Ising antiferromagnets ${\mathrm{Fe}}_{x}{\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{F}}_{2}$ and ${\mathrm{Mn}}_{x}{\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{F}}_{2}$. with $0<{H}_{0}<~20$ kOe parallel to $c$, large shifts in ${T}_{c}$ and dramatic changes in the shapes of the transition peaks were observed. These results confirm some, but not all, theoretical predictions and suggest an effective dimensionality $d\ensuremath{\simeq}2$. No ${H}_{0}$-induced rounding was observed. This is shown to be consistent with the rounding seen in other experiments at larger values of $\frac{g{\ensuremath{\mu}}_{\mathrm{B}}{H}_{0}}{k{T}_{c}}$.