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-onlyGd3+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 withTN=1.6K, which has been attributed to enhanced superexchange pathways facilitated by empty5degPt orbitals. In this study, we use various neutron scattering techniques on an isotopically enriched polycrystalline160Gd₂Pt₂O₇sample to examine the magnetic structure and spin-wave excitation spectrum belowTNin order to extract the dominant exchange interactions. We find that the ground-state magnetic structure is the Palmer-Chalker state previously seen in Gd₂Pt₂O₇ with an associated gapped excitation spectrum consistent with enhanced exchange interactions between further near-neighborGd3+ions. We confirm this exchange model with analysis of the magnetic diffuse scattering in the paramagnetic regime using polarized neutrons.