Dipolar spin ice regime proximate to an all-in-all-out N\'{e}el ground state in the dipolar-octupolar pyrochlore Ce$_2$Sn$_2$O$_7$

TL;DR

This study reveals that hydrothermally grown Ce$_2$Sn$_2$O$_7$ exhibits a dipolar spin ice phase near an all-in-all-out Neel order, contrasting with previous samples and highlighting the influence of synthesis methods on magnetic ground states.

Contribution

The paper provides the first characterization of Ce$_2$Sn$_2$O$_7$ using hydrothermal synthesis, demonstrating a proximate dipolar spin ice phase and contrasting it with prior findings of octupolar states in differently synthesized samples.

Findings

Hydrothermal Ce$_2$Sn$_2$O$_7$ shows broad low-wavevector neutron scattering signals.

The ground state is within the dipolar all-in-all-out Neel phase.

Previous samples indicated an octupolar quantum spin ice state.

Abstract

The dipolar-octupolar (DO) pyrochlores, R$_2$M$_2$O$_7$ (R = Ce, Sm, Nd), are key players in the search for realizable novel quantum spin liquid (QSL) states as a large parameter space within the DO pyrochlore phase diagram is theorized to host QSL states of both dipolar and octupolar nature. New single crystals and powders of Ce$_2$Sn$_2$O$_7$, synthesized by hydrothermal techniques, present an opportunity for a new characterization of the exchange parameters in Ce$_2$Sn$_2$O$_7$ using the near-neighbor $XYZ$ model Hamiltonian associated with DO pyrochlores. Utilizing quantum numerical linked cluster expansion fits to heat capacity and magnetic susceptibility measurements, and classical Monte Carlo calculations to the diffuse neutron diffraction of the new hydrothermally grown Ce$_2$Sn$_2$O$_7$ samples, we place Ce$_2$Sn$_2$O$_7$'s ground state within the ordered dipolar all-in-all-out (AIAO) N\'{e}el phase, with quantum Monte Carlo calculations showing a transition to long-range order at temperatures below those accessed experimentally. Indeed, our new neutron diffraction measurements on the hydrothermally grown Ce$_2$Sn$_2$O$_7$ powders show a broad signal at low scattering wave vectors, reminiscent of a \textit{dipolar} spin ice, in striking contrast from previous powder neutron diffraction on samples grown from solid-state synthesis, which found diffuse scattering at high scattering wave vectors associated with magnetic {\it octupoles} and suggested an octupolar quantum spin ice state. We conclude that new hydrothermally grown Ce$_2$Sn$_2$O$_7$ samples host a finite-temperature proximate dipolar spin ice phase, above the expected transition to AIAO N\'{e}el order.