Unconventional spin freezing and fluctuations in the frustrated antiferromagnet NiGa2S4

TL;DR

This study uses muon spin rotation experiments to reveal unconventional spin freezing and critical fluctuations in the 2D triangular antiferromagnet NiGa2S4, showing complex magnetic behavior below 8.5 K.

Contribution

It provides new insights into the spin dynamics and phase transition behavior of NiGa2S4, highlighting unconventional magnetic phenomena not seen in typical magnets or spin liquids.

Findings

Disordered Ni-spin freezing occurs below 8.5 K with long correlation times.

Exponential temperature dependence of muon spin relaxation indicates 2D critical fluctuations.

Slow spin fluctuations coexist with quasistatic magnetism and are field-dependent.

Abstract

Muon spin rotation (muSR) experiments reveal unconventional spin freezing and dynamics in the two-dimensional (2D) triangular lattice antiferromagnet NiGa2S4. Long-lived disordered Ni-spin freezing (correlation time > 10-6 s at 2 K) sets in below T_f = 8.5 +- 0.5 K with a mean-field-like temperature dependence. The observed exponential temperature dependence of the muon spin relaxation above T_f is strong evidence for 2D critical spin fluctuations. Slow Ni spin fluctuations coexist with quasistatic magnetism at low temperatures but are rapidly suppressed for fields > 10 mT, in marked contrast with the field-independent specific heat. The muSR and bulk susceptibility data indicate a well-defined 2D phase transition at T_f, below which NiGa2S4 is neither a conventional magnet nor a singlet spin liquid.