Interface and Volume Anisotropy of Mbe-Grown Co/Pt (111), (110) and (001) and Sputtered Co/Pt Multilayers
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INTERFACE AND VOLUME ANISOTROPY OF MBE-GROWN Co/Pt (111), (110) and (001) and SPUTTERED Co/Pt MULTILAYERS D. Weller, R.F.C. Farrow, R.F. Marks, G.R. Harp, H. Notarys, G. Gorman IBM Research Division, Almaden Research Center, San Jose CA 95120 * This work was supported in part by ONR. ABSTRACT A quantitative determination of interface (Ks) and volume anisotropy (Ko) constants of MBE and sputtered Co/Pt multilayers is reported. Torque and VSM magnetometry were used to determine the total average anisotropy and the room temperature magnetization of four different series of films with varying Co thickness and nearly constant Pt thickness. All films were characterized with X-ray diffraction and X-ray fluorescence, allowing the determination of the "magnetic" volume with good accuracy. Both Ks and KWfare found to be orientation dependent. We find the following results for MBE films grown on Ag buffered GaAs substrates and highly < 111 > textured films, grown on etched SiNx buffers: (111) Ks = 0.97mJ/m 2 , Kveff=-0.74MJ/m 3 MBE (111) Ks =0.92mJ/m 2 , Kveff=-l.l IMJ/m 3 sputtered Ks=0.42mJ/m 2, Kveff=-l.95MJ/m 3 MBE (110) (001) Ks=0.59mJ/m 2 , Kveff=-5.98MJ/m 3 MBE The [l10]-oriented MBE films show in addition a large (intrinsic) in-plane anisotropy constant K -'-3MJ/m 3 , which is found to be independent of the Co thickness. [100] is the easy and [1I0] the hard in-plane direction. 1. INTRODUCTION The structural and magnetic properties of Co/Pt multilayers are of continuing interest because of the potential for such multilayers as media for high-density magneto-optical recording in the blue spectral range. In 1990 Lee et al. [1, 2] demonstrated, via seeded epitaxy, the extreme dependence of magnetic anisotropy of Co/Pt multilayers on the orientation of the growth axis. Similar results had first been reported for textured [111] and [001] oriented Co/Pd multilayers [3] and were subsequently obtained for the three orientations of MBE grown Co/Pd superlattices [4] and more recently for Ni/Co/Ni sandwiches [5]. A variety of structural probes were used in the case of Co/Pt superlattices to investigate the degree of interface intermixing [6-8]. Chien et al. [9] suggested that perpendicularly aligned Co-Co pairs at stacking faults in a partially chemically ordered CoPt 3 phase at the interfaces might explain the orientation dependence including the strong uniaxial in-plane anisotropy for [1l0]-oriented multilayers. However, the density of stacking faults necessary to produce a considerable number of Co-Co pairs could not be confirmed [10, 11]. Nevertheless, short-range chemical ordering was detected in [11l]-oriented multilayers [12] using synchrotron X-ray diffraction. The percentage of ordered CoPt 3 phase was found to be large (-,80%) at 300 0 C growth temperature but only about 20% for the 100 0 C grown films, that are under investigation here. Thus one has to conclude that there is indeed the possibility of interfaces (or structural boundaries) between alloyed and/or chemically ordered compound regions and Co and Pt, which ca
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