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Extremely well isolated two-dimensional spin-1/2 antiferromagnetic Heisenberg layers with a small exchange coupling in the molecular-based magnet CuPOF

Opherden, D.; Nizar, N.; Richardson, K.; Monroe, J. C.; Turnbull, M. M.; Polson, M.; Vela, S.; Blackmore, W. J. A.; Goddard, P. A.; Singleton, J.; Choi, E. S.; Xiao, F.; Williams, R. C.; Lancaster, T.; Pratt, F. L.; Blundell, S. J.; Scurschii, I.; Uhlarz, M.; Ponomaryov, O.; Zvyagin, S.; Wosnitza, J.; Baenitz, M.; Heinmaa, I.; Stern, R.; Kühne, H.; Landee, C. P.

We report on a comprehensive characterization of the newly synthesized Cu2+-based molecular magnet [Cu(pz)2 (2-HOpy)2](PF6)2 (CuPOF), where pz = C4H4N2 and 2-HOpy = C5H4NHO. From a comparison of theoretical modeling to results of bulk magnetometry, specific heat, μ+SR, ESR, and NMR spectroscopy, this material is determined as an excellent realization of the two dimensional square-lattice S = 1/2 antiferromagnetic Heisenberg model with a moderate intraplane nearest-neighbor exchange coupling of J/kB = 6.80(5) K, and an extremely small interlayer interaction of about 1 mK. At zero field, the bulk magnetometry reveals a temperature-driven crossover of spin correlations from isotropic to XY type, caused by the presence of a weak intrinsic easy-plane anisotropy. A transition to long-range order, driven by the low-temperature XY anisotropy under the influence of the interlayer coupling, occurs at TN = 1.38(2) K, as revealed by μ+SR. In applied magnetic fields, our 1H-NMR data reveal a strong increase of the magnetic anisotropy, manifested by a pronounced enhancement of the transition temperature to commensurate long-range order at TN = 2.8 K and 7 T.

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Permalink: https://www.hzdr.de/publications/Publ-31484
Publ.-Id: 31484