Structural and magnetic properties of pseudo-two-dimensional triangular antiferromagnets Ba3MSb2O9 (M = Mn, Co, and Ni)

Abstract

The crystal structure and magnetic properties of 6H-perovskites Ba3MSb2O9 (M = Mn, Co, and Ni) were investigated. The M = Co and Ni compounds have a hexagonal structure with space group P63/mmc, while the Mn compound has a monoclinically distorted structure with space group C2/c. From the results of magnetic susceptibility and specific heat measurements, it was found that they show an antiferromagnetic transition at 10.0 K (for M = Mn), 3.8 K (Co) and 13.5 K (Ni), and the onset of the magnetic transition was observed much above TN. The powder neutron diffraction measurements for Mn and Co compounds were carried out, and their magnetic structures were determined. Both compounds adopt the non-collinear 120° structure in the ab-plane. These magnetic properties show the existence of a geometric magnetic frustration derived from the triangular array of magnetic M ions in the ab-plane.