NaCaNi2F7: A frustrated high temperature pyrochlore antiferromagnet with S=1 Ni2+

Abstract

NaCaNi${}_2$F${}_7$ is an insulating, frustrated A${}_2$B${}_2$F${}_7$ pyrochlore with magnetic S = 1 Ni${}^{2+}$ 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 ${\mu }_B$/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 = -${\theta }_{CW}$/T${}_f$ $\approx$ 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 NaCaNi${}_2$F${}_7$ is likely a realization of a frustrated spin 1 pyrochlore antiferromagnet with weak bond disorder.

15 Pages, 5 Figures, 2 Tables

Cited by in corpus (1)

• Static and dynamic XY-like short-range order in a frustrated magnet with exchange disorder