Extremely well isolated two-dimensional spin-12 antiferromagnetic Heisenberg layers with a small exchange coupling in the molecular-based magnet CuPOF

D. Opherden, HZDR - Helmholtz-Zentrum Dresden-Rossendorf
N. Nizar, Clark University
K. Richardson, Clark University
J. C. Monroe, Clark University
M. M. Turnbull, Clark University
M. Polson, University of Canterbury
S. Vela, Université de Strasbourg
W. J.A. Blackmore, University of Warwick
P. A. Goddard, University of Warwick
J. Singleton, National High Magnetic Field Laboratory Los Almos
E. S. Choi, Florida State University
F. Xiao, Durham University
R. C. Williams, Durham University
T. Lancaster, Durham University
F. L. Pratt, ISIS Neutron and Muon Source
S. J. Blundell, University of Oxford
Y. Skourski, HZDR - Helmholtz-Zentrum Dresden-Rossendorf
M. Uhlarz, HZDR - Helmholtz-Zentrum Dresden-Rossendorf
A. N. Ponomaryov, HZDR - Helmholtz-Zentrum Dresden-Rossendorf
S. A. Zvyagin, HZDR - Helmholtz-Zentrum Dresden-Rossendorf
J. Wosnitza, HZDR - Helmholtz-Zentrum Dresden-Rossendorf
M. Baenitz, Max Planck Institute for Chemical Physics of Solids
I. Heinmaa, National Institute of Chemical Physics and Biophysics, Tallinn
R. Stern, National Institute of Chemical Physics and Biophysics, Tallinn
H. Kühne, HZDR - Helmholtz-Zentrum Dresden-Rossendorf
C. P. Landee, Clark University

Abstract

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=12 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 H1-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.