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Magnetic order and disorder in a quasi-two-dimensional quantum Heisenberg antiferromagnet with randomized exchange

Xiao, F. and Blackmore, W. J. A. and Huddart, B. M. and Gomilšek, M. and Hicken, T. J. and Baines, C. and Baker, P. J. and Pratt, F. L. and Blundell, S. J. and Lu, H. and Singleton, J. and Gawryluk, D. and Turnbull, M. M. and Krämer, K. W. and Goddard, P. A. and Lancaster, T. (2020) 'Magnetic order and disorder in a quasi-two-dimensional quantum Heisenberg antiferromagnet with randomized exchange.', Physical review B., 102 (17). p. 144429.


We present an investigation of the effect of randomizing exchange coupling strengths in the S = 1/2 square lattice quasi-two-dimensional quantum Heisenberg antiferromagnet (QHAF) (QuinH)2Cu(ClxBr1−x )4 · 2H2O (QuinH = Quinolinium, C9H8N+), with 0 x 1. Pulsed-field magnetization measurements allow us to estimate an effective in-plane exchange strength J in a regime where exchange fosters short-range order, while the temperature TN at which long-range order (LRO) occurs is found using muon-spin relaxation, allowing us to construct a phase diagram for the series. We evaluate the effectiveness of disorder in suppressing TN and the ordered moment size, and we find an extended disordered phase in the region 0.4 x 0.8 where no magnetic order occurs. The observed critical substitution levels are accounted for by an energetics-based competition between different local magnetic orders. Furthermore, we demonstrate experimentally that the ground-state disorder is driven by quantum effects of the exchange randomness, which is a feature that has been predicted theoretically and has implications for other disordered quasi-two-dimensional QHAFs.

Item Type:Article
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Publisher statement:© 2020 American Physical Society
Date accepted:26 October 2020
Date deposited:26 October 2021
Date of first online publication:17 November 2020
Date first made open access:26 October 2021

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