Extreme Suppression of Antiferromagnetic Order and Critical Scaling in a Two-Dimensional Random Quantum Magnet

Sr2CuTeO6 is a square-lattice N ' eel antiferromagnet with superexchange between first-neighbor S = 1/2 Cu spins mediated by plaquette centered Te ions. Substituting Te by W, the affected impurity plaquettes have predominantly second-neighbor interactions, thus causing local magnetic frustration. Here we report a study of Sr2CuTe1-xWxO6 using neutron diffraction and mu SR techniques, showing that the N ' eel order vanishes already at x = 0.025 +/- 0.005. We explain this extreme order suppression using a two-dimensional Heisenberg spin model, demonstrating that a W-type impurity induces a deformation of the order parameter that decays with distance as 1/r(2) at temperature T = 0. The associated logarithmic singularity leads to loss of order for any x > 0. Order for small x > 0 and T > 0 is induced by weak interplane couplings. In the nonmagnetic phase of Sr2CuTe1-xWxO6, the mu SR relaxation rate exhibits quantum critical scaling with a large dynamic exponent, z approximate to 3, consistent with a random-singlet state.

Automated summary

In the study of Sr2CuTe1-xWxO6 using neutron diffraction and mu SR techniques, it was found that the Néel order vanishes at x = 0.025 +/- 0.005. A two-dimensional Heisenberg spin model was used to explain the extreme order suppression, where a W-type impurity induces a deformation of the order parameter with a logarithmic singularity leading to loss of order for any x > 0. In the nonmagnetic phase of Sr2CuTe1-xWxO6, the mu SR relaxation rate exhibits quantum critical scaling with a large dynamic exponent, z approximate to 3, consistent with a random-singlet state.