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arXiv · 1810.06399

Magnetic interactions and spin dynamics in the bond-disordered pyrochlore fluoride NaCaCo$_2$F$_7$

J. Zeisner·S. A. Bräuninger·L. Opherden·R. Sarkar·D. I. Gorbunov·J. W. Krizan·T. Herrmannsdörfer·R. J. Cava·J. Wosnitza·B. Büchner·H. -H. Klauss·V. Kataev
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Abstract

We report high-frequency/high-field electron spin resonance (ESR) and high-field magnetization studies on single crystals of the bond-disordered pyrochlore NaCaCo$_2$F$_7$. Frequency- and temperature-dependent ESR investigations above the freezing temperature $T_f \sim 2.4$ K reveal the coexistence of two distinct magnetic phases. A cooperative paramagnetic phase, evidenced by a gapless excitation mode, is found as well as a spin-glass phase developing below 20 K which is associated with a gapped low-energy excitation. Effective $g$-factors close to 2 are obtained for both modes in line with pulsed high-field magnetization measurements which show an unsaturated isotropic behavior up to 58 T at 2 K. In order to describe the field-dependent magnetization in high magnetic fields, we propose an empirical model accounting for highly anisotropic ionic $g$-tensors expected for this material and taking into account the strongly competing interactions between the spins which lead to a frustrated ground state. As a detailed quantitative relation between effective $g$-factors as determined from ESR and the local $g$-tensors obtained by neutron scattering [Ross et al., Phys. Rev. B 93, 014433 (2016)] is still sought after, our work motivates further theoretical investigations of the low-energy excitations in bond-disordered pyrochlores.

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J. Zeisner, S. A. Bräuninger, L. Opherden, R. Sarkar, D. I. Gorbunov, J. W. Krizan, T. Herrmannsdörfer, R. J. Cava, J. Wosnitza, B. Büchner, H. -H. Klauss, V. Kataev. 2019-04-01. Magnetic interactions and spin dynamics in the bond-disordered pyrochlore fluoride NaCaCo$_2$F$_7$. https://doi.org/10.1103/physrevb.99.155104

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