Magnetoresistance of Half-Metallic Oxide Nanocontacts

Magnetoresistive effects (R(0)-R(H))/R(H) exceeding $500%$ are found at room temperature in a field of 7 mT in nanocontacts between Fe₃O₄ crystallites. The shape of the $I(V)$ curve depends on field and the magnitude of the magnetoresistance is correlated with the resistance, the largest effects occurring when R>100kΩ. The explanation proposed involves hopping transport of spin-polarized electrons through a narrow domain wall pinned at the nanocontact; spin pressure on the domain wall pushes it out into the electrode, leading to the nonlinearity of the $I(V)$ characteristic. Application of current-induced wall motion in a simple fast-switching magnetic memory element is proposed.