High magnetoresistance ratio and high coercivity observed from epitaxial Co/Cu/Co/NiO spin valve sandwiches on MgO grown by molecular beam epitaxy

Abstract

Bottom and symmetrical Co/Cu/Co/NiO sandwiches are fabricated on single crystal substrates including MgO(100), MgO(110), and MgO(111) by molecular beam epitaxy without introducing a bias field. Although most of samples only show very weak exchange anisotropy, high magnetoresistance (MR) ratios (5%–8%) accompanied by high coercivities (200–2500 Oe) are observed. Strong angular dependence on Hc and MR has been also observed, which represents a uniaxial symmetry. The minor loops on the MR measurements have shown clear local MR maxima (minima) indicating that some intermediate antiparallel (parallel) spin states may exist.