Magnetic ground-state of strongly frustrated pyrochlore anti-ferromagnet Er_2Sn_2O_7

摘要

The experimental results of bulk magnetic susceptibility, isothermal magnetization and magnetic specific heat of the frustrated anti-ferromagnetic pyrochlore Er_2Sn_2O_7 are simulated and analyzed using appropriate crystal-field (CF) and molecular field tensors at Er-sites in the mean-field approach, which are found to be anisotropic along and normal to the local <111> axis of the frustrated tetrahedral spin-structure. Er-spins are constrained to lie in the local [111] easy-plane in the anti-ferromagnetic phase. Isothermal magnetization can be described by angle-averaged magnetization of the polycrystalline sample, expressed in terms of anisotropic g-tensors and exchange tensors. Temperature-dependent characteristic exchange splitting of the single-ion ground doublet describes the magnetic specific heat satisfactorily. The smaller exchange-splitting may cause rapid fluctuations of Er-spin moments in Er_2Sn_2O_7 and hence long-range ordering of Er-spins is not exhibited by Er_2Sn_2O_7 down to 100 mK, unlike in Er_2Ti_2O_7.