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PUBLISHED, High temperature ferromagnetism in thin films of dilute magnetic oxides is a widespread phenomenon, of which there appear to be two sources. One is the contribution of the 3d dopant ions themselves, the other is related to crystal defects in the interface region. The latter contributes a magnetic moment of 100?400??B per square nanometer of substrate area, which is largely independent of film thickness or dopant concentration. It is suggested that the defects are two-electron or two-hole centers which have a spin triplet as ground state or low-lying excited state. HfO2, an example of the former, is ferromagnetic even when undoped. In ZnO or SnO2, examples of the latter, the magnetic dopant may stabilize the spin triplet by exchange., This work was supported by Science Foundation Ireland, as part of the CINSE Project. The author is grateful to many coworkers, including L. S. Dorneles, C. B. Fitzgerald, R. Gunning, J. G. Lunney, M. Moliner, P. Stamenov, M. Venkatesan, and Y. Zhou. M. Konno of Hitachi Science Systems Ltd. kindly took the STEM image.

PUBLISHED, We report on field annealing effects in spin valves with an IrMn pinning layer and spin valves with a synthetic antiferromagnet. The exchange bias field and magnetoresistance of spin valves with an IrMn/CoFe bilayer at the bottom improve drastically upon annealing in large magnetic fields. The evolution of the exchange bias field with annealing field strength shows a rapid increase up to an applied field of 0.5 T, which is followed by a more gradual improvement up to an annealing field of 5.5 T. The increase of the exchange bias field in large magnetic fields indicates that the interfacial spin structure of the IrMn layer is directly influenced by the annealing field strength., The authors wish to acknowledge M. Venkatesan for SQUID measurements. This work was supported by Science Foundation Ireland as part of the CINSE program.

PUBLISHED, The conductivity of a nanocontact between two crystallites of magnetite (Fe3O4) was studied. It was found that the conductivity can increase sixfold at room temperature in an applied field of 7 mT (70 Oe). This large low-field effect was attributed to spin-polarized electrons hopping across a very narrow domain wall at the contact. Spin pressure on the domain wall at the nanocontact led to nonlinearity of the I(V) characteristic, and the possibility of fast switching in a bistable two- or three-terminal device via current-induced wall motion., This work was supported by the EU as part of the AMORE project in the growth program, and by Enterprise Ireland under Contract No. SC/99/225.