Regensburg 2019 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 47: Quantum Magnets, Molecular Magnets and Skyrmions
TT 47.2: Vortrag
Mittwoch, 3. April 2019, 15:15–15:30, H23
NMR of the two-dimensional S = 1/2 Heisenberg antiferromagnet CuPOF — •D. Dmytriieva1,2, Z. T. Zhang1, M. Uhlarz1, C. P. Landee3, J. Wosnitza1,2, and H. Kühne1 — 1Hochfeld-Magnetlabor Dresden (HLD-EMFL), HZDR, Dresden, Germany — 2Institut für Festkörper- und Materialphysik, TU Dresden, Germany — 3Department of Physics, Clark University, Worcester, Massachusetts, USA
The metal-organic compound [Cu(pz)2(2-OHpy)2](PF6)2 (CuPOF) is a molecular-based analog of the two-dimensional square-lattice quantum S = 1/2 Heisenberg antiferromagnet with well-isolated Cu(pz) layers and a very low kBTN/J = 0.21 ratio (J/kB = 6.8 K, TN = 1.38 K). We present a focus study of the low-T phase transition to long-range order, performed via 1H and 31P nuclear magnetic resonance (NMR) and high-field magnetometry. The very good agreement between the measured high-field magnetization and QMC simulations indicates an exceptional two-dimensionality of CuPOF, with an estimated ratio of the intra- to inter-plane exchange energies of J′/J ∝ 10−4. Within the ordered state, a splitting of the 1H NMR spectra reveals commensurate AF order, presumably of checkerboard type. A strong increase of TN in applied magnetic fields furthermore manifests the low dimensionality of CuPOF. A detailed analysis of the uniform magnetization and the 31P nuclear spin-lattice relaxation rate 1/T1 reveals an easy-plane anisotropy and a crossover from isotropic to XY behavior. Moreover, approaching the phase transition, the 31P relaxation rate indicates an exponential growth of the average inter-spin correlation length.