Unique Phase Transition on Spin-2 Triangular Lattice of Ag2MnO2

TL;DR

This paper investigates Ag2MnO2 as a candidate for an antiferromagnetic XY model on a triangular lattice, revealing a unique phase transition at 80 K linked to chirality and subsequent spin-glass behavior below 22 K.

Contribution

It reports the discovery of a novel phase transition related to chirality in a frustrated spin system, with detailed thermodynamic and magnetic analysis.

Findings

Second-order phase transition at 80 K indicated by specific heat

Smooth magnetic susceptibility across the transition

Spin-glass-like behavior below 22 K

Abstract

Ag2MnO2 is studied as a possible candidate compound for an antiferromagnetic XY spin model on a triangular lattice. In spite of the large Curie-Weiss temperature of -430 K found in magnetic susceptibi-lity, Mn3+ spins with S = 2 do not undergo a conventional long-range order down to 2 K probably owing to the geometrical frustration and two dimensionality in the system. Instead, a unique phase transition is found at 80 K, where specific heat exhibits a clear sign of a second-order phase transition, while magnetic susceptibility changes smoothly without a distinct anomaly. We think that this transition is related to the chirality degree of freedom associated with a short-range order, which has been expected for the classical XY spin model on a triangular lattice. On further cooling, spin-glass-like behavior is observed below 22 K, possibly corresponding to a quasi-long-range order.