Structural and Magnetoresistance Properties of Co/Cu Multilayers Doped with Fe
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STRUCTURAL AND MAGNETORESISTANCE PROPERTIES OF Co/Cu MULTILAYERS DOPED WITH Fe J.M. GEORGE*, A. BARTHELEMY*, 0. DURAND**, J. L. DUVAIL*, A. FERT*, P. GALTIER**, 0. HECKMANN***, L.G. PEREIRA*, F. PETROFF*, T. VALET** *Laboratoire de Physique des Solides, Universit6 Paris-Sud, 91405 Orsay, France "**Laboratoire Central de Recherches, Thomson CSF, 91404 Orsay, France ***Lboratoire pour l'Utilisation du Rayonnement Electromagn6tique, Universitl Paris-Sud, 91405 Orsay, France ABSTRACT We have studied the influence of ultra-thin interfacial Fe layers on the structural and magnetoresistance properties of Co/Cu multilayers. Our results show that the giant magnetoresistance arises from spin dependent scattering at the Co/Cu interfaces and in the bulk of Co, the interfacial contribution being predominant. We also demonstrate that the closepacked crystallographic structure of Co and Cu is very sensitive to the insertion of interfacial bcc Fe layers : for small thicknesses, Co as well as Cu adopt a metastable bcc structure. INTRODUCTION The giant magnetoresistance (MR), first discovered in epitaxial Fe/Cr(001) superlattices [1,2] has now been observed in a large variety of ferromagnetic/non-magnetic multilayered structures and very large MR have been recently reported for sputtered Co/Cu multilayers [3,4]. Planar doping, i.e. introducing thin interfacial layers of additional elements, is a powerful method to experimentally investigate the microscopic mechanisms of spin dependent scattering and the respective roles of interfacial versus bulk scattering. In this paper, we report on the MR of Co/Cu multilayers in which thin Fe layers are introduced at the interfaces. A structural study, based on X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and X-ray Absorption Spectroscopy (XAS), has also been performed. EXPERIMENTAL DETAILS The multilayers were prepared by ff diode sputtering in a Nordiko NS 2000 high-vacuum automated sputter deposition system with a base pressure in the 10-8 Torr range. Chemically etched Si(100) wafers were used as substrates and either Fe or Cr buffer layers (40A thick) were fast grown on the Si substrates. The films were then deposited at room temperature in an Ar pressure of 5 mTorr at typical deposition rates of 0.2-1 A/s. XRD measurements were performed in the 0-20 geometry on a two-axis spectrometer using CuKa radiation monochromated after the sample with the (002) reflection of pyrolitic graphite. TEM observations were made using a Topcon ABT 002B microscope operated at 200 kV. Plane views and cross sections were prepared by polishing and dimpling followed by argon milling. The XAS experiments were performed at the Laboratoire pour l'Utilisation du Rayonnement Electromagn6tique (LURE) on the DW21 synchrotron line using a Si(31 1) double crystal monochromator installed on the DCI storage ring. The variations of the X-ray absorption coefficient of some selected samples were measured above the K edges of Fe (7112 eV), Co (7709 eV) and Cu (8980 eV), in the total yield mode. MR measurements
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