Structure, spin correlations and magnetism of the $S = 1/2$ square-lattice antiferromagnet Sr$_2$CuTe$_{1-x}$W$_x$O$_6$ ($0 \leq x \leq 1$)

TL;DR

This study investigates the magnetic properties and spin correlations in the Sr$_2$CuTe$_{1-x}$W$_x$O$_6$ series, revealing complex magnetism, different ground states at specific compositions, and suggesting a potential quantum critical point.

Contribution

It provides new insights into the local spin correlations and the role of interlayer coupling in the Sr$_2$CuTe$_{1-x}$W$_x$O$_6$ system, highlighting its complex magnetic behavior.

Findings

Long-range magnetic order is suppressed for $x=0.05-0.6$.

Different local spin correlations observed at $x=0.2$ and $x=0.5$.

Interlayer coupling influences magnetic order suppression.

Abstract

Quantum spin liquids are highly entangled magnetic states with exotic properties. The $S = 1/2$ square-lattice Heisenberg model is one of the foundational models in frustrated magnetism with a predicted, but never observed, quantum spin liquid state. Isostructural double perovskites Sr$_2$CuTeO$_6$ and Sr$_2$CuWO$_6$ are physical realizations of this model, but have distinctly different types magnetic order and interactions due to a $d^{10}/d^0$ effect. Long-range magnetic order is suppressed in the solid solution Sr$_2$CuTe$_{1-x}$W$_x$O$_6$ in a wide region of $x = 0.05-0.6$, where the ground state has been proposed to be a disorder-induced spin liquid. Here we show that the spin-liquid-like $x = 0.2$ and $x = 0.5$ samples have distinctly different local spin correlations, which suggests they have different ground states. Furthermore, the previously ignored interlayer coupling between the square-planes is likely to play a role in the suppression of magnetic order on the W-rich side at $x \approx 0.6$. These results highlight the complex magnetism of Sr$_2$CuTe$_{1-x}$W$_x$O$_6$ and hint at a new quantum critical point at $x \approx 0.3$.