Short-range magnetic ordering process for the triangular lattice compound NiGa2S4: a positive muon spin rotation and relaxation study

TL;DR

This study investigates the magnetic ordering in NiGa2S4 using muon spin rotation, revealing three temperature regimes with distinct magnetic behaviors, including a continuous transition near 9.2 K and signs of topological defects.

Contribution

It provides new insights into the magnetic phase transitions and topological phenomena in the triangular lattice NiGa2S4 compound using muon spin techniques.

Findings

Observation of static magnetic fields below 9.2 K

Detection of multichannel relaxation between 9.2 K and 12.6 K

Evidence of topological defects above the transition temperature

Abstract

We report a study of the triangular lattice Heisenberg magnet NiGa2S4 by the positive muon spin rotation and relaxation technique. We unravel three temperature regimes: (i) below T_c = 9.2(2) K a spontaneous static magnetic field at the muon site is observed and the spin dynamics is appreciable: the time scale of the modes we probe is ~ 7 ns; (ii) an unconventional stretched exponential relaxation function is found for T_c < T < T_{cross} where T_{cross} = 12.6 K, which is a signature of a multichannel relaxation for this temperature range; (iii) above T_{cross}, the relaxation is exponential as expected for a conventional compound. The transition at T_c is of the continuous type. It occurs at a temperature slightly smaller than the temperature at which the specific heat displays a maximum at low temperature. This is reminiscent of the behavior expected for the Berezinskii-Kosterlitz-Thouless transition. We argue that these results reflect the presence of topological defects above T_c.