Structural Properties of Anisotropic PtCo(001) and PtFe(001) Thin Films on MgO(001)
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STRUCTURAL PROPERTIES OF ANISOTROPIC PtCo(001) AND PtFe(001) THIN FILMS ON MgO(001) Bruce M. Lairson, Mark R. Visokay, Sean B. Brennan, Robert Sinclair, and Bruce M. Clemens, Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305-2205 ABSTRACT We report structural properties of PtFe and PtCo intermetallic compounds with perpendicular magnetic anisotropy and a preferred c-axis orientation perpendicular to the film plane, formed from initially epitaxial multilayers. These materials represent particular cases of a more general class of anisotropic magnetic compounds with the CuAu(1) natural superlattice structure. They possess high magneto-optic Kerr rotations and magnetizations, suggesting them as likely candidates for magneto-optic and perpendicular magnetic recording media. INTRODUCTION In the Pt/Co and Pt/Fe multilayer systems, stacking along the [001] direction, with single monolayers of Co or Fe, and Pt, constituting a bilayer period, in each case produces a natural superlattice with large magneto-crystalline anisotropy. The formation of these natural PtCo and PtFe superlattices in thin film form with the c axis out of the plane of the substrate is therefore interesting. These tetragonal intermetallic compounds have Curie temperatures from 400 to 500'C. PtCo thin films have previously been prepared with the (111) planes crystallographically textured parallel to the film plane[I], but these had relatively small perpendicular magnetic anisotropy because the [001] magnetically easy axes of the tetragonal grains were oriented 550 away from the sample normal. Increased perpendicular anisotropy is expected if the tetragonal grains are oriented with their c-axes
perpendicular to the film plane. We have recently reported a technique for producing natural superlattice PtFe and PtCo thin films, with the [001] axis oriented preferentially out of the film plane, using epitaxial multilayers as precursors[2,3]. These films exhibited large perpendicular magnetic anisotropy. The natural superlattices are formed by annealing epitaxial Pt/Fe and Pt/Co artificial superlattices stacked along the Pt [001] direction. This thin film structure is of interest because of the high magneto-optic Kerr rotations available from PtCo and PtFe alloys and intermetallic compounds[4], the relatively large magnetization of PtCo, and its thermodynamic stability. We have also recently reported magneto-optic Kerr rotations from the ordered phases which are up to 60% larger than those of the disordered phases[5]. Epitaxial multilayers were grown by sputtering onto epitaxial Pt(001) oriented substrate layers. These substrate layers were deposited onto polished single crystals of MgO(001) using a seeding technique described elsewhere[6]. The equiatomic multilayers consisted of multiple bilayers of Pt/Fe and Pt/Co deposited at 100 0C. This yielded epitaxial multilayer structures with the [001] cube axes of the FCC Pt, FCC Co, and BCC Fe oriented out of the plane of the sample. X-ray diffraction detected no other phases p
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