Microstructural modification in Co/Cu giant-magnetoresistance multilayers

Three different classes of [Co/1.1 nm/Cu/2.1 nm]30 multilayers were grown by magnetron sputtering deposition. The effect of magnetostatic interactions on the giant-magnetoresistance (GMR) and magnetic properties are examined in relation to the induced changes in the film microstructure as it is varied by: (i) the substrate surface roughness and (ii) the effect of thermal isolation of the Si(100) substrate from the cooling plate during deposition. A remarkable variation in shape and magnitude of GMR, and in the magnetic (M-H) loops, is observed for the three classes of films. It is found that there are three characteristic features in every sample that vary systematically: (i) The (ΔR/R)max ratio. (ii) The magnetic field range where a GMR loop reaches its minimum value. (iii) The (M-H) loops that vary from the characteristic antiferromagnetic to a typical ferromagnetic loop shape. Two well-separated grain size distributions below and above 12 nm were found from transmission electron microscopy. The smaller grains are associated with the appearance of a considerable fraction of ferromagnetically coupled regions in the multilayer.