NaCaNi2F7 is an insulating, frustrated A2B2F7 pyrochlore with magnetic S = 1 Ni2+ on the pyrochlore B site. Non-magnetic Na and Ca are disordered on the A-site. Magnetic susceptibility measurements made on an oriented single crystal, grown in a floating zone furnace, show isotropic behavior at temperatures between 5 and 300 K, with an effective moment of 3.7 μB/Ni. Despite displaying a large Curie-Weiss theta (-129 K), spin-ordering-related features are not seen in the susceptibility or specific heat until a spin glass transition at 3.6 K. This yields an empirical frustration index of f = -θCW/Tf≈ 36. The spin glass behavior is substantiated by a shift of the freezing temperature with frequency in the AC susceptibility, bifurcation in the DC susceptibility, and by a broad maximum in the magnetic specific heat. The observations as made on large single crystals suggest that NaCaNi2F7 is likely a realization of a frustrated spin 1 pyrochlore antiferromagnet with weak bond disorder.
@article{arxiv.1504.07708,
title = {NaCaNi2F7: A frustrated high temperature pyrochlore antiferromagnet with S=1 Ni2+},
author = {J. W. Krizan and R. J. Cava},
journal= {arXiv preprint arXiv:1504.07708},
year = {2015}
}