High sensitivity in magnetoresistance of epitaxial NiFe/Cu/Co (/Cu) (100) superlattices

Noncoupled-type [NiFe/Cu/Co(/Cu)] single-crystal-like superlattices were prepared on Si/Cu(100) substrates using ultrahigh vacuum evaporation. Si/Cu (5 nm)/[Co (3 nm)/Cu (6 nm)/NiFe (3 nm)/Cu (6 nm)]×10 multilayers showed 6.1% magnetoresistance (MR) change with 2 kA/m of applied field, which is much higher sensitivity than those of poly-crystalline films. Furthermore, placing a thin Ag layer (0.2 nm) at the midpoint of a Cu layer improved the MR sensitivity of the epitaxial film. Sandwich-type Si/Cu (5 nm)/NiFe (10 nm)/Cu (2.4 nm)/Ag (0.2 nm)/Cu (2.4 nm)/Co (10 nm) superlattice showed sharp switching characteristics of the MR curve between lower and 4.3% higher resistivity. These epitaxial films showed biaxial anisotropy in the film plane with easy axes of [011] and [01̄1] directions. The higher MR sensitivity in the epitaxial films may originate in the square-shaped magnetization curves along the easy axes [011] and [01̄1] of the Co layers. Flatness of interface was also effective to improve the MR sensitivity of the films.