Spin dynamics and spin freezing in the triangular lattice antiferromagnets FeGa2S4 and NiGa2S4

Article

关键词: QUANTUM ANTIFERROMAGNETS;    PHASE-TRANSITIONS;    HEISENBERG-ANTIFERROMAGNET;    MAGNETIC-PROPERTIES;    NEEL ORDER;    STATES;   

DOI  :  10.1103/PhysRevB.86.064435

来源: SCIE

【 摘 要 】

Magnetic susceptibility and muon spin relaxation (mu SR) experiments have been carried out on the quasi-2D triangular-lattice spin S = 2 antiferromagnet FeGa2S4. The mu SR data indicate a sharp onset of a frozen or nearly frozen spin state at T* = 31(2) K, twice the spin-glass-like freezing temperature T-f = 16(1) K. The susceptibility becomes field dependent below T*, but no sharp anomaly is observed in any bulk property. A similar transition is observed in mu SR data from the spin-1 isomorph NiGa2S4. In both compounds the dynamic muon spin relaxation rate lambda(d)(T) above T* agrees well with a calculation of spin-lattice relaxation by Chubukov, Sachdev, and Senthil in the renormalized classical regime of a 2D frustrated quantum antiferromagnet. There is no firm evidence for other mechanisms. At low temperatures, lambda(d)(T) becomes temperature independent in both compounds, indicating persistence of spin dynamics. Scaling of lambda(d)(T) between the two compounds is observed from similar to T-f to similar to 1.5T*. Although the mu SR data by themselves cannot exclude a truly static spin component below T*, together with the susceptibility data they are consistent with a slowly fluctuating spin gel regime between T-f and T *. Such a regime and the absence of a divergence in lambda(d)(T) at T* are features of two unconventional mechanisms: (1) binding/unbinding of Z(2) vortex excitations, and (2) impurity spins in a nonmagnetic spin-nematic ground state. The absence of a sharp anomaly or history dependence at T* in the susceptibility of FeGa2S4, and the weakness of such phenomena in NiGa2S4, strongly suggest transitions to low-temperature phases with unconventional dynamics.

【 授权许可】

Free