  A recently discovered material, 6H-B-Ba3NiSb2O9 was found to display unusual
low-temperature phenomenology, interpreted as a quantum spin liquid with spin S
= 1 on a triangular lattice. We study a spin S = 1 quantum exchange model on an
AB stacked triangular lattice near its quantum paramagnet-to-spiral magnet
transition, driven by easy-plane single-ion anisotropy. We demonstrate that the
frustrated inter- and intra-layer exchange interactions induce contour lines of
low energy excitations that lead to a broad crossover regime of
linear-temperature dependence of the specific heat. Based on this and a variety
of other predictions, we argue that the observed phenomenology can be
understood in terms of a conventional picture of a proximity to this frustrated
critical point.
