Relief of Frustration in the Heisenberg Pyrochlore Antiferromagnet Gd$_2$Pt$_2$O$_7$

TL;DR

This study investigates Gd$_2$Pt$_2$O$_7$, revealing a strongly first-order antiferromagnetic transition at 1.6 K with a gapped excitation spectrum, and shows that platinum's electronic structure helps relieve frustration, promoting magnetic order.

Contribution

It demonstrates that platinum cations facilitate superexchange interactions, increasing the ordering temperature and partially relieving frustration in Gd$_2$Pt$_2$O$_7$ compared to other gadolinium pyrochlores.

Findings

Gd$_2$Pt$_2$O$_7$ orders antiferromagnetically at 1.6 K

The transition is strongly first order with a gapped spectrum

Platinum cations help relieve magnetic frustration

Abstract

The gadolinium pyrochlores, Gd$_2B_2$O$_7$, are amongst the best realizations of antiferromagnetically coupled Heisenberg spins on a pyrochlore lattice. We present a magnetic characterization of Gd$_2$Pt$_2$O$_7$, a unique member of this family. Magnetic susceptibility, heat capacity, and muon spin relaxation measurements show that Gd$_2$Pt$_2$O$_7$ undergoes an antiferromagnetic ordering transition at $T_N = 1.6$ K. This transition is strongly first order, as indicated by the sharpness of the heat capacity anomaly, thermal hysteresis in the magnetic susceptibility, and a non-divergent relaxation rate in $\mu$SR. The form of the heat capacity below $T_N$ suggests that the ground state is an anisotropic collinear antiferromagnet with an excitation spectrum that is gapped by 0.245(1) meV. The ordering temperature in Gd$_2$Pt$_2$O$_7$, $T_N = 1.6$ K, is a substantial 160% increase from other gadolinium pyrochlores, which have been found to order at 1 K or lower. We attribute this enhancement in $T_N$ to the $B$-site cation, platinum, which, despite being non-magnetic, has a filled $5d$ $t_{2g}$ orbital and an empty $5d$ $e_g$ orbital that can facilitate superexchange. Thus, the magnetic frustration in Gd$_2$Pt$_2$O$_7$ is partially "relieved", thereby promoting magnetic order.