Spin dependent impurity effects in the 2D frustrated magnetism of NiGa$_2$S$_4$

TL;DR

This study investigates how different magnetic impurities affect the spin states in NiGa$_2$S$_4$, revealing that integer Heisenberg spins help maintain a 2D frozen spin-disordered state, while others induce spin glass phases.

Contribution

It demonstrates the role of impurity spin size and anisotropy in stabilizing or disrupting the 2D spin-disordered state in NiGa$_2$S$_4$, providing new insights into impurity effects in frustrated magnets.

Findings

Zn$^{2+}$ and Fe$^{2+}$ substitutions preserve the 2D disordered state.

Co$^{2+}$ and Mn$^{2+}$ induce conventional spin glass phases.

Integer Heisenberg spins are crucial for stabilizing the 2D state.

Abstract

Impurity effects on the triangular antiferromagnets Ni$_{1-x}M_x$Ga$_2$S$_4$ ($M=$ Mn, Fe, Co and Zn) are studied. The 2D frozen spin-disordered state of NiGa$_2$S$_4$ is stable against the substitution of Zn$^{2+}$ ($S=0$) and Heisenberg Fe$^{2+}$ ($S=2$) spins, and exhibits a $T^2$-dependent magnetic specific heat, scaled by the Weiss temperature. In contrast, the substitutions with Co$^{2+}$ ($S=3/2$) spin with Ising-like anisotropy and Heisenberg Mn$^{2+}$ ($S=5/2$) spin induce a conventional spin glass phase. From these comparisons, it is suggested that integer size of Heisenberg spins is important to stabilize the 2D coherent behavior observed in the frozen spin-disordered state.