Effect of dilution on the critical behaviour of a dipolar uniaxial ferromagnet: Magnetic susceptibility of LiTb0.5Y0.5F4

Abstract

The parallel and perpendicular susceptibility of a single crystal of LiTb_0.5Y_0.5F₄ has been measured in the temperature range 0.32-4.2K. A ferromagnetic transition occurs at T_c=1.119K instead of 2.890K for pure LiTbF₄. The critical behaviour of the parallel susceptibility has been accurately studied in the range 5*10^-4-1, where t=(T-T_c)/T_c. A marked effect of dilution by yttrium has been observed. In contrast with pure LiTbF₄ where chi /sub /// is well fitted by the theoretically predicted law for uniaxial dipolar ferromagnets (i.e. the classical law with small logarithmic corrections), the usual power law t^{- gamma} with gamma =1.215 seems to hold in LiTb_0.5Y_0.5F₄. This could be related to a reduction of effective dimensionality with dilution.