Structural and magnetic properties of the new low-dimensional spin magnet InCu2/3V1/3O3

We report structural and magnetic data of a new transition metal oxide InCu2/3V1/3O3 containing hexagonal planes of magnetic Cu2+ (S = 1/2) ions in a 5-fold trigonal-bipyramidal coordination of oxygen ions. Static magnetic susceptibility and electron spin resonance (ESR) data as well as numerical quantum Monte-Carlo calculations suggest that Cu spins in the layers are strongly antiferromagnetically coupled with J similar to 140 K and form a two-dimensional S = 1/2-Heisenberg honeycomb lattice. Owing to the appreciable interlayer coupling the compound orders magnetically at 38K. Remarkably, ESR gives evidence that the orbital ground state of Cu2+ is not the x(2) - y(2) orbital as in copper oxides with the usual octahedral, square-pyramidal or square-planar coordination, but it is the 3z(2) - r(2) orbital, which is unique for the cuprates. (c) 2004 Elsevier B.V. All rights reserved.