Exchange coupling in sputtered giant magnetoresistance NiFe/Cu/CoFe/Cu multilayers

We will report on the exchange coupling, magnetoresistance (MR) and film structure in the system NiFe/Cu/CoFe/Cu as a function of multilayer number (bilayers=6 to 20) and Cu spacing (5 to 31 A). The multilayers were prepared by sputter deposition and investigated by x‐ray diffraction (XRD), atomic force microscopy (AFM), vibrating sample magnetometry (VSM), ferromagnetic resonance (FMR), and standard MR methods. The exchange coupling, Hex, and MR are shown to vary with Cu spacing. The XRD data indicates the multilayer structure is evolving through at least the first 20 bilayers. AFM measurements suggest subtle variations in interface quality and a rms roughness near 0.4 nm. These variations in structure are manifested in the FMR and MR. Multilayers with Cu spacers ≳11 A generally show the expected two FMR peaks. Some multilayers show three peaks indicating defects within the multilayer. These defects can be viewed as the elusive ‘‘pinholes’’ which act to ferromagnetically short the magnetic layers togethe...