Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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Magnetic interactions and spin dynamics in the bond-disordered pyrochlore fluoride NaCaCo2F7
Zeisner, J.; Bräuninger, S. A.; Opherden, L.; Sarkar, R.; Gorbunov, D. I.; Krizan, J. W.; Herrmannsdörfer, T.; Cava, R. J.; Wosnitza, J.; Büchner, B.; Klauss, H. H.; Kataev, V.;
We report high-frequency/high-field electron spin resonance (ESR) and high-field magnetization studies on single crystals of the bond-disordered pyrochlore NaCaCo2F7. Frequency- and temperature-dependent ESR investigations above the freezing temperature Tf ∼ 2.4 K reveal the coexistence of two distinct magnetic phases. A cooperative paramagnetic phase, evidenced by a gapless excitation mode, is found along with 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.

Publ.-Id: 29085 - Permalink