Effect of interface roughness on the exchange bias for NiFe/FeMn

The effect of interface roughness on exchange bias for NiFe/FeMn bilayers is investigated for polycrystalline films and epitaxial films. Three different systems were investigated: polycrystalline Ta (10 nm)/Ni80Fe20 (10nm)/Fe50Mn50 (20 nm) films on oxygen plasma-etched Si(100) or Cu/H–Si(100) and epitaxial Ni80Fe20 (10nm)/Fe60Mn40 (20 nm) films on Cu/H–Si(110). For films grown on plasma-etched substrates, as the etching time is increased, film roughness increases up to 12 nm. For the polycrystalline films grown on ultrathin Cu underlayers, x-ray diffraction shows the fcc (111) texture is greatly reduced as the thickness is increased. The epitaxial Cu/Si(110) buffer layer induces fcc (111) epitaxial growth and modifies the interface morphology. The dependence of exchange bias on roughness for each set of samples is explained in terms of a competition between the interfacial exchange coupling and the af uniaxial anisotropy.