Field-induced quantum ordered phases in an anisotropic Haldane system

Abstract

Field-induced quantum ordered phases in the anisotropic S = 1 Haldane system are studied, using an effective Lagrangian formalism. We predict that, when the applied field is inclined from the principal axes of the spin anisotropy, successive phase transitions occur from the Haldane phase to a field-induced ordered phase followed by another spin-reorientation transition from the one to other field-induced ordered phase at high fields. Depending on the anisotropy constants, the spin-reorientation transition is of the first order or of the second order via another type of the ordered phase. Relevant implications of these transitions are further discussed in connection with the novel ordered phase recently observed in the Haldane system, NDMAP, at high fields.