Magnetic structure and exchange interactions in the Heisenberg pyrochlore antiferromagnet Gd2Pt2O7

Abstract

The Heisenberg pyrochlore antiferromagnet Gd 2 Pt 2 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 Gd 3+ Heisenberg interaction model, the gadolinium pyrochlore series exhibits various complex magnetic ground states at low temperature. Gd 2 Pt 2 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 e g Pt orbitals. In this study, we use various neutron scattering techniques on an isotopically enriched polycrystalline 160 Gd 2 Pt 2 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 Gd 2 Sn 2 O 7 with an associated gapped excitation spectrum consistent with enhanced exchange interactions between further near-neighbor Gd 3+ ions. We confirm this exchange model with analysis of the magnetic diffuse scattering in the paramagnetic regime using polarized neutrons.

Spinteract: a program to refine magnetic interactions to diffuse scattering data

“…The Spinteract code has already been successfully used in several published studies [23,24,69,70], allowing it to be tested on a variety of problems. The systems considered include the intermetallic Gd 2 PdSi 3 , in which determination of the magnetic interactions helped to explain the origin of the skyrmion crystal observed under small applied magnetic fields [23]; the honeycomb-lattice magnet NaNi2BiO 6−δ , in which evidence of a large Kitaev interaction was obtained [24]; and the breathing pyrochlore LiGaCr 4 S 8 , in which trends in interaction values identified using Spinteract were shown to agree qualitatively with density-functional-theory predictions [69].…”

“…If these checks suggest that the results are not well constrained by the data, the user has two options-either fix some parameters, or include more experimental data. A particularly useful approach is to fit to bulk magnetic susceptibility data as well as magnetic diffuse scattering, as in references [18,23,70]. The magnetic susceptibility expressed as χ T effectively measures the Q → 0 limit of the magnetic diffuse scattering, and provides a strong constraint on the net value of the magnetic interactions (i.e.…”