Muon spin rotation (μSR) 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 Tf 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 μSR and bulk susceptibility data indicate a well-defined 2D phase transition at Tf, below which NiGa2S4 is neither a conventional magnet nor a singlet spin liquid.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 2008 Dec 1|