Abstract
We present powder and single-crystal neutron diffraction and bulk measurements of the Kagomé-staircase compound (NVO) in fields up to applied along the direction. (The Kagomé plane is the plane.) This system contains two types of Ni ions, which we call “spine” and “cross-tie.” Our neutron measurements can be described with the paramagnetic space group for and each observed magnetically ordered phase is characterized by the appropriate irreducible representation(s). Our zero-field measurements show that at NVO undergoes a transition to a predominantly longitudinal incommensurate structure in which the spine spins are nearly along the -axis. At , there is a transition to an elliptically polarized incommensurate structure with both spine and cross-tie moments in the plane. At the system undergoes a first-order phase transition to a commensurate antiferromagnetic structure with the staggered magnetization primarily along the -axis and a weak ferromagnetic moment along the -axis. A specific heat anomaly at indicates an additional transition, which remarkably does not affect Bragg peaks of the commensurate C structure. Neutron, specific heat, and magnetization measurements produce a comprehensive temperature-field phase diagram. The symmetries of the incommensurate magnetic phases are consistent with the observation that only one phase is electrically polarized. The magnetic structures are explained theoretically using a simplified model Hamiltonian, that involves competing nearest- and next-nearest-neighbor exchange interactions, single-ion anisotropy, pseudodipolar interactions, and Dzyaloshinskii-Moriya interactions.
14 More- Received 13 October 2005
DOI:https://doi.org/10.1103/PhysRevB.74.014429
©2006 American Physical Society