Magnetic structure and exchange interactions in the Heisenberg pyrochlore antiferromagnet Gd2Pt2O7

The Heisenberg pyrochlore antiferromagnet Gd2Pt2O7 is one of a series of gadolinium pyrochlore compounds with a variety of B-site cations. Despite the expected simplicity of a spin-only Gd3+ Heisenberg interaction model, the gadolinium pyrochlore series exhibits various complex magnetic ground states at low temperature. Gd2Pt2O7 displays the highest temperature magnetic order of the series with T-N = 1.6 K, which has been attributed to enhanced superexchange pathways facilitated by empty 5d e(g) Pt orbitals. In this study, we use various neutron scattering techniques on an isotopically enriched polycrystalline (Gd2Pt2O7)-Gd-160 sample to examine the magnetic structure and spin-wave excitation spectrum below T-N in order to extract the dominant exchange interactions. We find that the ground-state magnetic structure is the Palmer-Chalker state previously seen in Gd2Sn2O7 with an associated gapped excitation spectrum consistent with enhanced exchange interactions between further near-neighbor Gd3+ ions. We confirm this exchange model with analysis of the magnetic diffuse scattering in the paramagnetic regime using polarized neutrons.