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 NMR — Rajib Sarkar¹, •Felix Brückner¹, Jason W. Krizan², Robert J. Cava², and Hans-Henning Klauss¹ — ¹Institut 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)