We recently reported the observation of room temperature ferromagnetism in mixtures of ZnO and Co3O4 despite the diamagnetic and antiferromagnetic character of these oxides respectively. Here we present a detailed study on the electronic structure of this material in order to account for this unexpected ferromagnetism. Electrostatic interactions between both oxides lead to a dispersion of Co3O4 particles over the surface of ZnO larger ones. As a consequence, the reduction of Co+3 to Co2+ at the particle surface takes place as evidenced by XAS measurements and optical spectrocopy. This reduction allows to xplain the observed ferromagnetic signal within the well established theories of magnetism.
@article{arxiv.0912.3458,
title = {Surface magnetism in ZnO/Co3O4 mixtures},
author = {M. A. Garcia and F. Jimenez-Villacorta and A. Quesada and J. de la Venta and N. Carmona and I. Lorite and J. Llopis and J. F. Fernandez},
journal= {arXiv preprint arXiv:0912.3458},
year = {2015}
}