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 (Formula presented) 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 U(Formula presented)isotropic dipolar (ID)→Gaussian crossovers. While the U(Formula presented)ID crossover is sharply defined and occurs at (Formula presented) the I(Formula presented)Gaussian crossover proceeds without the (theoretically predicted) intervening isotropic short-range Heisenberg regime and takes place over a wide temperature range. © 1999 The American Physical Society.