Extremely Well Isolated Two-Dimensional Spin-1/2 Antiferromagnetic Heisenberg Layers With A Small Exchange Coupling In The Molecular-Based Magnet Cupof

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, mu+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/k(B) = 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 T-N = 1.38(2) K, as revealed by mu+SR. In applied magnetic fields, our H-1-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 T-N = 2.8 K and 7 T.