MEASUREMENT OF STATIC CRITICAL EXPONENTS FOR A STRUCTURAL ISING-MODEL PHASE-TRANSITION WITH RANDOM STRAINS - DY(ASXV1-X)O4

The critical exponents beta, delta, and gamma have been measured for the tetragonal-orthorhombic phase transition in Dy(AsxV1-x)O4. For pure DYVO4 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 beta, delta, and gamma for the two mixed samples agree well with each other: gamma increases to 1.55 compared to 1.15 for pure DYVO4, and delta increases to 5.8 compared to 4.1 for DYVO4. However, beta remains unchanged near 0.33 within experimental error. Although the increase in gamma is consistent with exponents expected for the random-field Ising model, the result for beta is not. The measured exponents satisfy the scaling relation gamma = beta(delta - 1) within the experimental uncertainties, and together with another scaling relation, alpha + 2beta + gamma = 2, allow us to infer that the critical specific-heat behavior changes from divergent (alpha > 0) in pure sample to cusplike (alpha < 0) in the mixed samples.