Characterization of the order-annealing response of nanostructured iron-palladium based ferromagnetic thin-films
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Characterization of the order-annealing response of nanostructured iron-palladium based ferromagnetic thin-films Huiping Xu1), Adam T. Wise1), Timothy J. Klemmer2) and Jörg M. K. Wiezorek 1) 1) Department of Materials Science & Engineering, University of Pittsburgh, 848 Benedum Hall, Pittsburgh, PA 15261, USA; 2) Seagate Technology, 2403 Sidney Street, Pittsburgh, PA 15203, USA; Abstract A combination of XRD and TEM techniques have been used to characterize the response of room temperature magnetron sputtered Fe-Pd thin films on Si-susbtrates to post-deposition order-annealing at temperatures between 400-500˚C. Deposition produced the disordered Fe-Pd phase with (111)-twinned grains approximately 18nm in size. Ordering occurred for annealing at 450˚C and 500˚C after 1.8ks, accompanied by grain growth (40-70nm). The ordered FePd grains contained (111)-twins rather than {101}-twins typical of bulk ordered FePd. The metallic overlayers and underlayers selected here produced detrimental dissolution (Pt into Fe-Pd phases) and precipitation reactions between Pd and the Si substrate. Introduction Tetragonal intermetallic phases, such as FePt, CoPt, MnAl and FePd, are of interest as active ferromagnetic materials in thermally stable high-information density thin film data storage media [1]. Due to their high magnetocrystalline anisotropy (~107-108 erg/cm3) theoretical estimates predict thermally stable grain sizes resistant to spontaneous magnetization reversal in the range of approximately 3-5nm for these intermetallics [2]. Utilization of these intermetallic phases, which derive their attractive magnetic properties from their tetragonal ordered L10-type crystal structures with an easy magnetization axis parallel to the c-direction, promises up to about one order of magnitude increase in data storage densities with respect to current Co-based media. Recent research on ferromagnetic intermetallic thin films for potential storage media applications focused mostly on FePt, CoPt and on property measurements, whereas relatively little published work on the structural evolution of FePd thin films during post-deposition treatments exists. FePd thin films have been grown successfully by molecular beam epitaxy (MBE) [3] and by magnetron sputtering on Pt-underlayers on MgO substrates [4]. The latter method allows more rapid deposition and is currently popularly employed in most industrial operations. Unlike MBE, magnetron sputtering without substrate heating usually produces intermetallic films that consist of the disordered solid solution rather than the ordered phases. In principle, substrate heating can be used to induce ordering during deposition but is usually accompanied by undesirable grain growth, producing less than optimal magnetization behavior [4]. Post-deposition annealing procedures that induce the ordering transformation offer potential control of the ordered phase grain size in room temperature sputtered Fe-Pd thin films. The development of optimized processing strategies for these nanostructured intermetallic materi
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