Observation of isotropic dipolar to uniaxial dipolar crossover in gadolinium

Abstract

Extensive high-resolution magnetic-susceptibility (χ ) measurements have been performed along the c axis (easy direction of magnetization) of a high-purity gadolinium single crystal in the reduced temperature range 5.1×10^-5<~ε =(T-T^C)/TC≤1.2×10^-1. The results of an elaborate data analysis permit the first accurate determination of asymptotic critical exponent for χ and unambiguously demonstrate that the asymptotic critical behavior of gadolinium is that of a uniaxial dipolar (UD) ferromagnet. In addition, present results using existing data on critical spin dynamics provide conclusive evidence for the occurrence of UD→isotropic dipolar (ID)→ Gaussian crossovers. While the UD→ID crossover is sharply defined and occurs at ε _COUD→ID=2.05(10)×10^-3, the ID?Gaussian crossover proceeds without the (theoretically predicted) intervening isotropic short-range Heisenberg regime and takes place over a wide temperature range.