Half-metallic oxide point contacts

A classification of half-metals is illustrated with examples of ferromagnetic and ferrimagnetic oxides. I : V characteristics and magnetoresistance of contacts between oxides with localized electrons (Fe3O4) and delocalized electrons ((La0.7Sr0.3)MnO3) are discussed. The magnetoresistance is large when the conductance of the contact is less than the quantum of conductance G0 = 2e 2 /h . Broad distributions of point contacts are investigated in pressed powder compacts, illustrated by powder magnetoresistance measurements of CrO2, (La0.7Sr0.3)MnO3 and Fe3O4. When exchange coupling exists across an atomic scale contact, a narrow domain wall of width comparable to the contact size may be pinned there. Some consequences are thermal magnetic mode fluctuations, nonlinear I : V characteristics due to electron pressure on the wall and current-induced switching in a bistable ‘peanut’ device with two closely spaced nanoconstrictions.