Quantum Disordered State In The J(1)-J(2) Square-Lattice Antiferromagnet Sr2cu(Te0.95w0.05)O-6

The B-site ordered double perovskites Sr2Cu(Te1-xWx)O-6 provide an excellent arena for investigating exotic phases expected for the J(1)-J(2) square-lattice Heisenberg antiferromagnet. Here, combining magnetic susceptibility and specific-heat measurements with electron spin resonance (ESR) and muon spin rotation/relaxation (p.SR) techniques, we explore a spin-liquid-like state in the vicinity of the Neel critical end point (x = 0.05-0.1). The specific heat and the ESR and muon relaxation rates give evidence for an energy hierarchy of low-energy excitations, reminiscent of randomness-induced singlet states. In addition, the weak transverse mu SR data show a fraction of frozen magnetic moments in the random-singlet background. The origin of a random-singlet-like state near the phase boundary is discussed in terms of concomitant exchange randomness and local strain generated by the W6+-for-Te6+ substitution.