Cooperative Two-Sublattice Model for Frustrated Pyrochlore Gd₂FeSbO₇

DC and AC magnetization and heat capacity data of frustrated pyrochlore Gd₂FeSbO₇ are studied within the framework of cooperative two-sublattice model [1] in presence of easy-plane single-ion anisotropy at Gd-site. There are three types of interactions: intra-sublattice Gd-Gd antiferromagnetic interaction, intra-sublattice Fe-Fe ferromagnetic interaction, and inter-sublattice Gd-Fe antiferromagnetic interaction. The interaction between Fe³⁺ 3d moments, which is stronger than 4f⁷ interaction, generates a molecular field at Gd-site through a weaker cooperative Gd-Fe ramification. Fe³⁺ sublattice orders at T_C ~ 5 K possibly in ‘two-in, two-out’ spin-configuration due to FM exchange interaction. Gd moments are fixed perpendicular to local <111> axes of tetrahedron due to crystal-field anisotropy and antiferromagnetic Gd-Gd exchange interactions. Such magnetic structure for Gd tetrahedra may resemble the Palmer-Chalker ground state, which is subdued due to stronger B-site Fe-Fe interactions. Saturation magnetization of 13.04μ_B is expressed as the vector coupling of directional magnetic moments of Gd and Fe. Finally magnetocaloric properties of Gd₂FeSbO₇ are estimated from magnetization and heat capacity results.

[1] S. Nandi et al. , Journal of Alloys and Compounds 714, 318 (2017).