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Berlin 2018 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 100: Frustrated Magnets - Pyrochlore Oxides

TT 100.6: Talk

Thursday, March 15, 2018, 17:00–17:15, H 3005

Spin freezing in disordered pyrochlore magnets probed by NMRRajib Sarkar1, •Felix Brückner1, Jason W. Krizan2, Robert J. Cava2, and Hans-Henning Klauss11Institut für Festkörper- und Materialphysik, Technische Universität Dresden, Germany — 2Department of Chemistry, Princeton University, USA

The frustrated pyrochlore magnets NaACo2F7 (A = Ca2+, Sr2+) exhibit a mixed A-site with a random distribution of Na+ and Ca2+/Sr2+. To investigate the effect of the resulting bond-disorder, we performed 23Na and 19F NMR experiments. While the Curie-Weiss temperature is ∼140 K (A = Ca) respective ∼ 130 K (Sr), the spin freezes at around 3 K, which gives high frustration indices of around 45. In fact, the 23Na and 19F broaden substantially below 3.6 K accompanied by a considerable reduction of the NMR signal intensity. A progressive slow-down of spin fluctuations is observed as per a BPP-like curvature of the 19F spin-lattice relaxation rate. Eventually this ends up in a spin frozen state below 3.6 K in NaCaCo2F7. The hyperfine coupling to the magnetic moments increases significantly in this region. In addition to that, we present a simulation of 23Na NMR spectra and compare it to results of a DFT calculation.
Phys. Rev. B 89, 214401 (2014)
Phys. Rev. B 95, 144414 (2017)
R. Sarkar et al. (accepted in PRB)

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