Magnetic structure and exchange interactions in the Heisenberg pyrochlore antiferromagnet Gd2Pt2O7

Abstract

The Heisenberg pyrochlore antiferromagnet ${\mathrm{Gd}}_{2}{\mathrm{Pt}}_{2}{\mathrm{O}}_{7}$ is one of a series of gadolinium pyrochlore compounds with a variety of B-site cations. Despite the expected simplicity of a spin-only ${\mathrm{Gd}}^{3+}$ Heisenberg interaction model, the gadolinium pyrochlore series exhibits various complex magnetic ground states at low temperature. ${\mathrm{Gd}}_{2}{\mathrm{Pt}}_{2}{\mathrm{O}}_{7}$ 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 $5d\phantom{\rule{0.16em}{0ex}}{e}_{g}$ Pt orbitals. In this study, we use various neutron scattering techniques on an isotopically enriched polycrystalline $^{160}\mathrm{Gd}{}_{2}{\mathrm{Pt}}_{2}{\mathrm{O}}_{7}$ 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 ${\mathrm{Gd}}_{2}{\mathrm{Sn}}_{2}{\mathrm{O}}_{7}$ with an associated gapped excitation spectrum consistent with enhanced exchange interactions between further near-neighbor ${\mathrm{Gd}}^{3+}$ ions. We confirm this exchange model with analysis of the magnetic diffuse scattering in the paramagnetic regime using polarized neutrons.