Spin-liquid-like state in a spin-1/2 square-lattice antiferromagnet perovskite induced by d 10 – d 0 cation mixing

A quantum spin liquid state has long been predicted to arise in spin-1/2 Heisenberg square-lattice antiferromagnets at the boundary region between Néel (nearest-neighbor interaction dominates) and columnar (next-nearest-neighbor interaction dominates) antiferromagnetic order. However, there are no known compounds in this region. Here we use d 10 – d 0 cation mixing to tune the magnetic interactions on the square lattice while simultaneously introducing disorder. We find spin-liquid-like behavior in the double perovskite Sr 2 Cu(Te 0.5 W 0.5 )O 6 , where the isostructural end phases Sr 2 CuTeO 6 and Sr 2 CuWO 6 are Néel and columnar type antiferromagnets, respectively. We show that magnetism in Sr 2 Cu(Te 0.5 W 0.5 )O 6 is entirely dynamic down to 19 mK. Additionally, we observe at low temperatures for Sr 2 Cu(Te 0.5 W 0.5 )O 6 —similar to several spin liquid candidates—a plateau in muon spin relaxation rate and a strong T -linear dependence in specific heat. Our observations for Sr 2 Cu(Te 0.5 W 0.5 )O 6 highlight the role of disorder in addition to magnetic frustration in spin liquid physics.