Specific-heat critical behavior of the structural random-field system Dy(AsxV1-x)O4.

Abstract

The specific-heat critical behaviors of the pure Ising transition in ${\mathrm{DyVO}}_{4}$ and the random-field Ising transition in Dy(${\mathrm{As}}_{\mathit{x}}$${\mathrm{V}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$)${\mathrm{O}}_{4}$ have been measured. The critical exponent \ensuremath{\alpha} and amplitude ratio ${\mathit{A}}^{+}$/${\mathit{A}}^{\mathrm{\ensuremath{-}}}$ for ${\mathrm{DyVO}}_{4}$, which has ${\mathit{T}}_{\mathit{c}}$=14.82 K, are in excellent agreement with the known pure d=3 Ising exponents. The random fields generated by the local strain fields in Dy(${\mathrm{As}}_{\mathit{x}}$${\mathrm{V}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$)${\mathrm{O}}_{4}$ depress the transitions to ${\mathit{T}}_{\mathit{c}}$=13.45 K and ${\mathit{T}}_{\mathit{c}}$=7.7 K for x=0.05 and x=0.15, respectively. With increasing x, the transition becomes rounded and severely depressed in size. The value of \ensuremath{\alpha} appears large and negative for x=0.15. As the random-field strength increases, i.e., the value of x gets larger, the amount of entropy change associated with the transition rapidly decreases. Where the missing entropy reappears is not adequately understood. \textcopyright{} 1996 The American Physical Society.