Measurement of static critical exponents for a structural Ising-model phase transition with random strains: Dy(AsxV1-x)O4.

Abstract

The critical exponents \ensuremath{\beta}, \ensuremath{\delta}, and \ensuremath{\gamma} have been measured for the tetragonal-orthorhombic phase transition in Dy(${\mathrm{As}}_{\mathit{x}}$${\mathrm{V}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$)${\mathrm{O}}_{4}$. For pure ${\mathrm{DyVO}}_{4}$ the exponents are close to Ising d=3 values. For x=0.05 and x=0.154 the random strain fields arising from As-V substitutions depress the transition temperature and alter the critical behavior. The exponents \ensuremath{\beta}, \ensuremath{\delta}, and \ensuremath{\gamma} for the two mixed samples agree well with each other: \ensuremath{\gamma} increases to 1.55 compared to 1.15 for pure ${\mathrm{DyVO}}_{4}$, and \ensuremath{\delta} increases to 5.8 compared to 4.1 for ${\mathrm{DyVO}}_{4}$. However, \ensuremath{\beta} remains unchanged near 0.33 within experimental error. Although the increase in \ensuremath{\gamma} is consistent with exponents expected for the random-field Ising model, the result for \ensuremath{\beta} is not. The measured exponents satisfy the scaling relation \ensuremath{\gamma}=\ensuremath{\beta}(\ensuremath{\delta}-1) within the experimental uncertainties, and together with another scaling relation, \ensuremath{\alpha}+2\ensuremath{\beta}+\ensuremath{\gamma}=2, allow us to infer that the critical specific-heat behavior changes from divergent (\ensuremath{\alpha}g0) in pure sample to cusplike (\ensuremath{\alpha}0) in the mixed samples.