Study of Crystal-field Interaction in Magnetic Frustrated Lead Pyrochlore Gd_2Pb_2O_7

摘要

A fine tuning between the crystal field and the molecular field to adopt unique ground state in frustrated magnetic R_2M_2O_7 pyrochlores structures is made by the variation of chemical pressure at R-site caused by substitution of nonmagnetic cation of M-site. Existence of larger cation at M -site increases the lattice parameter or nearest-neighbor bond distance between magnetic R-spins, and causes subtle changes to the local oxygen environment surrounding each R-ion, thereby reduces the chemical pressure at R-site which leads to a dramatic change in the crystal-field and molecular field. To investigate the effect of chemical pressure, the experimental results of powder magnetic susceptibility and isothermal magnetization of the frustrated compound Gd2Pb2O_7 containing largest cation, e.g. lead (Pb), at M~(4+)-sites were simulated and analyzed employing a D_(3d) crystal-field (CF) and anisotropic molecular field at R-sites in the self-consistent mean-field approach. The second-ordered axial parameter B20 and total CF splitting of the ground multiplet Gd-ion in Gd2Pb2O_7 are 477 cm~(-1) and 4.8 cm~(-1) respectively which are the lowest among their isomorphous counterparts, implying reduced effect of the crystal-field at Gd site in Gd_2Pb_2O_7.