Coherent Behavior and Nonmagnetic Impurity Effects of Spin Disordered State in NiGa₂S₄

Abstract

Nonmagnetic impurity effects of the spin disordered state in the triangular\nantiferromagnet NiGa$_2$S$_4$ was studied through magnetic and thermal\nmeasurements for Ni$_{1-x}$Zn$_x$Ga$_2$S$_4$ (0.0\\le x\\le 0.3). Only 1 %\nsubstitution is enough to strongly suppress the coherence observed in the spin\ndisordered state. However, the suppression is not complete and the robust\nfeature of the T^2 dependent specific heat and its scaling behavior with the\nWeiss temperature indicate the existence of a coherent Nambu-Goldstone mode.\nAbsence of either conventional magnetic order or bulk spin freezing suggests a\nnovel symmetry breaking of the ground state.\n