The magnetoresistance origin of FeCo nanocontacts with current-perpendicular-to-plane spin-valve structure (invited).

We have developed the FeCo nanocontact magnetoresistance (NCMR) with spin-valve structure [H. N. Fuke et al., IEEE Trans. Magn. 43, 2848 (2007)] which exhibits up to a MR ratio of 11%–12% at a resistance area (RA) of 0.3–0.55 Ω μm2. The nanocontact configurations were estimated at about 2 nm in in-plane diameter, 1.2 nm in thickness, and 0.55% in density for a RA∼0.5 Ω μm2 film based on in-plane current distribution by conductive atomic-force microscopy cross sectional transmission electron microscope images of the NCMR. The origin of the NCMR was discussed by comparing magnetic field dependence of resistance, with micromagnetics simulation based on the diffusive MR theory. It is found that our NCMR cannot be explained by diffusive domain wall theory or bulk scattering in free and pinned layers. It is likely that a theory on the basis of a ballistic MR consideration is needed to interpret our MR origin. [ABSTRACT FROM AUTHOR]