Spin alignment in, and electronic and magnetic properties of small Co-O molecules

Magnetoelectronic properties of small atomic clusters composed of Co and O atoms have been calculated from the first principles in the Hartree-Fock (HF) approximation. It has been found that the smallest Co-O molecules are "antiferromagnetic" singlets, with uncompensated electron spins localized on Co atoms, while somewhat larger Co-O molecules are "ferromagnetic," with parallel spins localized on Co atoms. The stretchable O-O bond in such Co-O molecules can accommodate small geometrical changes that may facilitate spin realignment in antiferromagnetic HF singlet Co-O molecules converting such molecules to ferromagnetic HF triplets and pentets. Such spin realignment is energetically favorable and can lead to reconstruction of the antiferromagnet-ferromagnet interface to provide for minimization of the surface energy in exchange-biased core-shell Co/Co-O nanoclusters. In its turn, this interface reconstruction may lead to a loss of exchange bias in small Co-O nanoclusters. (C) 2010 American Institute of Physics. [doi:10.1063/1.3340458]