Investigation by spherical neutron polarimetry of magnetic properties in BaCo2(ASO4)2

The cobaltite BaCo2(ASO(4))(2) (BCAO) is a good realization of the quasi-2D system in which the Co2+ ions form a magnetically frustrated honeycomb lattice with magnetic moments mainly confined in the basal planes. Below T-N = 5.35 +/- 0.5 K, the ground state structure is described by an incommensurate propagation vector k approximate to (0.265, 0, -1.33) and the magnetic excitation spectrum displays a resolution-limited energy gap do P Delta(0) approximate to 1.45meV at q = 0. No magnetic excitations emerging from q = k could be detected, contrary to what would be expected for a simple helimagnetic ground state. In order to understand these puzzling results, we have recently re-investigated the magnetic structure and excitations in BCAO using spherical neutronpolarization analysis. (c) 2006 Elsevier B.V. All rights reserved.