Estimation of single-ion anisotropies, crystal-field and exchange interactions in Gd-based frustrated pyrochlore anti-ferromagnets Gd_2M_2O_7 (M=Ti, Sn, Hf, Zr)

摘要

The temperature dependence of the experimental results of dc (macroscopic) magnetic susceptibility and nuclear hyperfine properties of frustrated magnetic Gd-based pyrochlore compounds, Gd_2Ti_2O_7, Gd_2Sn_2O_7, Gd_2Hf_2O_7 and Gd_2Zr_2O_7, are analyzed within the frame work of appropriate crystal-field theory and a mean field approximation by introducing effective anisotropic molecular field tensors, and formulating an exact relation between single-ion susceptibility tensors and site susceptibility tensors. Components of the calculated susceptibility along and perpendicular to the local < 1 1 1 > axis of the tetrahedral sublattice of pyrochlore structure show that these pyrochlores are easy-planar anisotropic magnetic systems. The crystal-field parameters and anisotropic exchange coupling have been determined and their systematic variations over the Gd-based pyrochlores studied here are discussed.