Abstract
Ag 2 MnO 2 is studied as a possible candidate compound for an antiferromagnetic X Y spin model on a triangular lattice. In spite of the large Curie–Weiss temperature of -430 K found in magnetic susceptibility, Mn 3+ 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 X Y 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.
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