Physical properties of spin-valve films grown on naturally oxidized metal nano-oxide surfaces

The physical properties of spin-valve films NiFe 25 A/CoFe 10 A/Cu(tCu)/CoFe 30 A/IrMn 70 A/Ta 20 A with graded Cu layer thickness (tCu=18–45 A) grown on the surface of metal nano-oxide layers (NOLs) were studied. The NOLs were formed from ultrathin Al, Cr, Cu, Nb, Ta, CoFe, NiFe, and NiFeCr layers by natural oxidation. The growth of the spin-valve films on NOLs has led to an enhancement in giant magnetoresistance value by up to 48%. A corresponding reduction in minimum film resistance by over 10% confirms that this enhancement originates from an increase in the mean free path of spin-polarized electrons due to the resultant specular reflection at the nano-oxide surfaces. A wide spectrum of oscillatory interlayer exchange coupling dependence on tCu for these NOL-bearing films suggests that a specular nano-oxide surface does not necessarily result in a smoother multilayer structure. The observation of an enhanced exchange biasing among these spin-valve films appears in contradiction to the observed deterio...