Effects of dislocations in triangular antiferromagnet NiGa2S4*

NiGa2S4 is a frustrated magnet on a triangular lattice with a strong antiferromagnetic third-neighbor exchange J3 and a weak ferromagnet first-neighbor exchange J1. Although the system has been studied for more than a decade [1], its behavior, particularly the lack of long-range order, remains poorly understood. Exotic scenarios have been proposed for its explanation, including the formation of a quadrupolar spin order that cannot be seen by the usual probes like neutrons [2]. We propose a different scenario based on a simple observation: the geometrical frustration of NiGa2S4 can be relieved by a lattice distortion similar to the case of the pyrochlore antiferromagnet [3]. Based on a generalized Imry-Ma argument, the spin-Peierls phase transition may be preempted by long-range-correlated strains of random edge dislocations. Using Monte Carlo simulation, we show that the ground state domain pattern matches the pattern of strain field from dislocations.

[1] S. Nakatsuji, Science 309, 1697 (2005).

[2] A. Läuchli, F. Mila, and K. Penc, Phys. Rev. Lett. 97, 467 (2006).

[3] O. Tchernyshyov, R. Moessner, and S. L. Sondhi, "Spin-Peierls phases in pyrochlore antiferromagnets," Phys. Rev. B 66, 357 (2002).