Modelling the Berezinskii-Kosterlitz-Thouless Transition in the NiGa_2S_4

TL;DR

This paper proposes a phenomenological model demonstrating that the spin-freezing transition in NiGa_2S_4 is a Berezinskii-Kosterlitz-Thouless (BKT) transition, characterized by power-law decayed spin correlations, linking 2D superfluidity concepts to magnetic systems.

Contribution

It introduces a new phenomenological model showing the BKT transition in a real magnetic system, NiGa_2S_4, connecting experimental observations to theoretical phase transition frameworks.

Findings

The spin-freezing transition in NiGa_2S_4 is of BKT type.

The spin correlations in NiGa_2S_4 decay as a power law.

The model explains the experimental NMR results.

Abstract

In the two-dimensional superfluidity, the proliferation of the vortices and the anti-vortices results in a new class of phase transition, Berezinskii-Kosterlitz-Thouless (BKT) transition. This class of the phase transitions is also anticipated in the two-dimensional magnetic systems. However, its existence in the real magnetic systems still remains mysterious. Here we propose a phenomenological model to illustrate that the novel spin-freezing transition recently uncovered in the NMR experiment on the NiGa_2S_4 compound is the BKT-type. The novel spin-freezing state observed in the NiGa_2S_4 possesses the power-law decayed spin correlation.