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

Journal article

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.

Authors: Xiao, F; Blackmore, WJA; Huddart, BM; Gomilsek, M; Hicken, TJ

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Physical Society
• Journal: Physical Review B
• Volume: 102
• Issue: 17
• Article number: 174429
• Publication date: 2020-11-17
• Acceptance date: 2020-10-26
• DOI: 10.1103/PhysRevB.102.174429
• EISSN: 2469-9969
• ISSN: 2469-9950
• Language: English
• Keywords: FFR