Transmission Electron Microscopy Study of CoPt(001) and FePt(001) Films Formed from Epitaxial Co/Pt and Fe/Pt Multilayer
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TRANSMISSION ELECTRON MICROSCOPY STUDY OF CoPt(001) AND FePt(001) FILMS FORMED FROM EPITAXIAL Co/Pt AND Fe/Pt MULTILAYERS M.R. VISOKAY, B.M. LAIRSON, B.M. CLEMENS and R. SINCLAIR Department of Materials Science and Engineering Stanford University, Stanford CA 94305
ABSTRACT Transmission electron microscopy was performed on epitaxial Fe/Pt and Co/Pt [001] oriented multilayers that were sputter deposited onto single crystal [001] MgO. Films were examined as-deposited and after annealing in vacuum. Before annealing, the films had a magnetic easy axis in the plane while after annealing the easy axis was out of the plane. Perpendicular anisotropies of 8x 106 erg/cm 3 and 1.9x 10' erg/cm3 were measured for the Fe/Pt and Co/Pt post-annealed films. Large magneto-optic Kerr rotations were also measured, 0.60 and 0.40 for the Fe/Pt and Co/Pt annealed films, respectively. Changes in the magnetic properties were a direct result of the transformation of the multilayer into c axis oriented FePt and CoPt intermetallic compounds upon annealing.
INTRODUCTION Thin film multilayer structures, particularly those involving Pt as the nonmagnetic and Fe or Co as the magnetic layers, have received a great deal of attention recently owing to their potential application for magneto-optic recording media. Typically these films are produced by stacking along the Pt [111] direction, and it has been shown that a [111] texture in these as-deposited multilayers often results in superior properties compared to other growth orientations[ I]. Other classes of materials that may also have promise for magneto-optic applications are ordered intermetallic compounds, of which FePt and CoPt are examples. These materials adopt the tetragonal Li 0 crystal structure, and in the case of FePt and CoPt the c axis is magnetically easy, with a large uniaxial magnetocrystalline anisotropy[2]. A thin film oriented with the magnetically easy c-axis normal to the film plane would be likely to possess remanent perpendicular magnetization, as required for magneto-optic recording media. Additionally, FePt and CoPt alloys are known to have substantial magneto-optic Kerr rotations, another requirement for this type of recording[3,4]. Therefore thin films with [001] oriented Lio structures are attractive for possible magneto-optic application. Recently we have shown that one route to producing the [001] oriented natural superlattices FePt and CoPt is to anneal epitaxial artificially synthesized multilayers stacked along the Pt [001] direction[5,6]. As the films transform from the multilayer to the ordered Lio structure the magnetic and magneto-optic properties improve dramatically. This paper will describe the magnetic properties of the Fe/Pt and Co/Pt films and, using cross-section transmission electron microscopy (TEM), correlate these properties with the microstructure and orientation relationships observed before and after annealing.
EXPERIMENTAL Epitaxial Fe/Pt and Co/Pt multilayer thin films were produced by DC planar magnetron sputtering in argon onto 1001] orien
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