A comparative study of the magnetic ordering specific heats of four [formula omitted] dipolar magnets: LiRF 4 (R = Er, Dy, Ho, Tb)

Abstract

Low temperature specific heat data are presented on LiRF 4 with R = Er, Dy, Ho, and compared with published results for LiTbF 4. The compounds LiHoF 4 and LiTbF 4 are dipolar Ising ferromagnets, ordering at T c = 1.530 and 2.885 K, respectively, whereas LiErF 4 and LiDyF 4 are dipolar XY antiferromagnets, with T c = 0.380 and 0.605 K. The shapes of the specific heat anomalies are compared. The different types of dipolar ordering can be understood on the basis of the crystal field anisotropy for the rare earth electronic ground state, which is a doublet (or pseudo-doublet) in all four cases, with g∥ ⪢ g ⊥ for R = Ho, Tb, and g ⊥ ⪢ g∥ for R = Er, Dy. The energies involved in the magnetic ordering as obtained from integration of the specific heat curves are found to be in good agreement with the lowest-energy configurations predicted by Misra and Felsteiner for these dipolar systems.