Regensburg 2022 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 12: Correlated Electrons: Materials
TT 12.6: Vortrag
Dienstag, 6. September 2022, 10:45–11:00, H22
NMR investigations of a quasi-two-dimensional Heisenberg antiferromagnet under pressure — •F. Bärtl1,2, D. Opherden1,2, C. P. Landee3, S. Molatta1,2, J. Wosnitza1,2, M. Baenitz4, 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 — 4MPI for Chemical Physics of Solids, Dresden, Germany
The molecular-based material [Cu(pz)2(2-HOpy)2](PF6)2 (CuPOF) is an excellent realization of a two-dimensional square-lattice quantum S=1/2 Heisenberg antiferromagnet, with an intralayer exchange coupling J/kB = 6.8 K and an interlayer coupling J′ ≈ 10−4J. Previously reported nuclear magnetic resonance (NMR) data revealed a low-temperature transition to a commensurate antiferromagnetic (AF) quasistatic long-range order (LRO), with a preceding crossover from isotropic Heisenberg to anisotropic XY behavior. We present further NMR studies of the low-temperature correlations in magnetic fields up to 7 T and temperatures down to 0.3 K. The application of hydrostatic pressure up to 10 kbar leads to a change of the interlayer coupling and, therefore, the magnetic correlations in the critical regime. The transition regime is probed by 1H and 31P spectroscopy and relaxometry, revealing a monotonic change of TN with increasing pressure. The commensurate AF LRO below TN persists at high pressures, as revealed by a splitting of the 1H NMR lines, stemming from the broken symmetry of the local spin polarizations in the LRO regime.