Evidence for an exotic magnetic transition in the triangular spin system FeGa 2S 4

Abstract

We report positive muon spin relaxation measurements on the triangular lattice magnetic system FeGa 2S 4. A magnetic transition that, to the best of our knowledge, has not been previously detected by specific-heat and magnetic susceptibility measurements is found in zero field at T *30 K. It is observed through the temperature dependencies of the signal amplitude and the spin-lattice relaxation rate. This transition is therefore not a conventional magnetic phase transition. Since persistent spin dynamics is observed down to 0.1 K, the ground state cannot be of the canonical spin-glass type, which could be suggested from hysteresis effects in the bulk susceptibility below T f16 K. These results are compared to those found for the isomorph NiGa 2S 4. It is argued that the fate of the transition, which has been interpreted in terms of the Z 2 topological transition in this latter system, is probably different in FeGa 2S 4. © 2012 American Physical Society.