Order by disorder and spiral spin liquid in frustrated diamond lattice antiferromagnets

TL;DR

This paper investigates how frustration in diamond lattice antiferromagnets leads to a highly degenerate ground state and a spiral spin-liquid regime, with order-by-disorder mechanisms influencing the transition to magnetic order.

Contribution

It introduces a model for frustrated diamond lattice antiferromagnets, revealing a spiral surface and spin-liquid behavior, and connects these findings to experimental observations in MnSc2S4.

Findings

Identification of a spiral surface in momentum space.

Observation of a broad spiral spin-liquid regime.

Agreement with experimental data on MnSc2S4.

Abstract

Frustration refers to competition between different interactions that cannot be simultaneously satisfied, a familiar feature in many magnetic solids. Strong frustration results in highly degenerate ground states, and a large suppression of ordering by fluctuations. Key challenges in frustrated magnetism are characterizing the fluctuating spin-liquid regime and determining the mechanism of eventual order at lower temperature. Here, we study a model of a diamond lattice antiferromagnet appropriate for numerous spinel materials. With sufficiently strong frustration a massive ground state degeneracy develops amongst spirals whose propagation wavevectors reside on a continuous two-dimensional ``spiral surface'' in momentum space. We argue that an important ordering mechanism is entropic splitting of the degenerate ground states, an elusive phenomena called order-by-disorder. A broad ``spiral spin-liquid'' regime emerges at higher temperatures, where the underlying spiral surface can be directly revealed via spin correlations. We discuss the agreement between these predictions and the well characterized spinel MnSc2S4.