Magnetic structure of layered Co2B2O5 and the role of the bridging B2O5 anions in three-dimensional magnetic ordering

Abstract

The single crystals of pyroborate Co2B2O5 have been synthesized using a flux method and have been characterized using X-ray diffraction, scanning electron microscopy, and thermogravimetric measurements. The crystal, electronic, and magnetic structures have been studied by density functional theory combined with representation analysis. The calculations predict the ground magnetic state is collinear antiferromagnetic described by the propagation vector k = (0, ½, ½), where the ferromagnetic layers built of the Co2+O6 octahedra separated by [B2O5]4- groups are antiferromagnetically coupled. The Co magnetic moments are aligned along the [101] direction and nearly lie in the plane of [B2O5]4- groups.The multiple collinear and noncollinear magnetic structures with k = (0, 0, 0), (½, 0, 0), and (0, ½, ½) lie in the close vicinity of the ground magnetic state and could be stabilized by the external magnetic field and temperature. The calculations of the exchange interactions revealed the crucial role of the exchange paths via bridging [B2O5]4- anions in the long-range magnetic order.