Sign of the superexchange coupling between next-nearest neighbors in EuO

The sign of the superexchange coupling J sub(2) between next-nearest neighboring Eu super(2+) magnetic moments in EuO is a matter subject to debate. We have obtained evidence that this coupling is of antiferromagnetic nature (J sub(2) < 0). EuO thin films grown at different temperatures suggest that lattice expansion results in enhancement of T sub(C) as clearly observed in stoichiometric EuO films grown on CaF sub(2) substrates. Resonant photoemission spectroscopy provides compelling evidence of strong hybridization between O 2p and Eu 5d6s6p weighted bands, suggesting that strong superexchange may be mediated by oxygen, thus consistent with the observed antiferromagnetic behavior between the next-nearest neighboring Eu atoms via nearest neighbor oxygen in EuO.