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

抄録

Nonmagnetic impurity effects of the spin disordered state in the triangular antiferromagnet NiGa₂S₄ were studied through magnetic and thermal measurements for Ni_1−xZn_xGa₂S₄ (0.0≤x≤0.3). Only 1% substitution is enough to strongly suppress the coherence observed in the spin disordered state. However, the suppression is not complete and the robust feature of the T²-dependent specific heat and its scaling behavior with the Weiss temperature indicate the existence of a coherent Nambu–Goldstone mode. The absence of either conventional magnetic order or bulk spin freezing suggests a novel symmetry breaking of the ground state.