SPECIFIC-HEAT CRITICAL BEHAVIOR OF THE STRUCTURAL RANDOM-FIELD SYSTEM DY(ASXV1-X)O-4

摘要

The specific-heat critical behaviors of the pure Ising transition in DyVO4 and the random-field Ising transition in Dy(AsxV1-x)O-4 have been measured. The critical exponent alpha and amplitude ratio A(+)/A(-) for DyVO4, which has T-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(As,V1-x)O-4 depress the transitions to T-c=13.45 K and T-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 alpha appears large and negative for x=0.15. As the random-held 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. [References: 24]