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TT: Fachverband Tiefe Temperaturen
TT 63: Quantum Magnets and Molecular Magnets (joint session TT/MA)
TT 63.6: Vortrag
Donnerstag, 19. März 2020, 16:45–17:00, HSZ 304
Field tunability of BKT correlations in the square-lattice Heisenberg antiferromagnet CuPOF — •D. Opherden1,2, C. P. Landee3, F. Bärtl1,2, M. Uhlarz1, Y. Skourski1, A. N. Ponomaryov1, S. A. Zvyagin1, 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 realization of the 2D square-lattice S = 1/2 Heisenberg antiferromagnet with well-separated Cu(pz) layers and a moderate intraplane coupling J/kB=6.8 K. We present a focus study of the low-T phase transition to long-range order, performed via 1H and 31P nuclear magnetic resonance and bulk magnetometry. A weak intrinsic easy-plane anisotropy, revealed by magnetization data, yields a temperature-driven crossover of the spin-exchange anisotropy from isotropic Heisenberg to anisotropic XY-type behavior. The application of a magnetic field normal to the easy-plane yields a field-driven increase of the magnetic anisotropy with the occurrence of Berezinskii-Kosterlitz-Thouless correlations, revealed by results of the 31P spin-lattice relaxation rate close to the transition temperature to long-range order. A detailed analysis of the temperature-dependent order parameter demonstrates the possibility for a continuous tuning of the spin-exchange anisotropy in CuPOF, from almost ideal isotropic Heisenberg to nearly XY-type exchange at elevated fields.