On the atomic interdiffusion in Co/Pt superlattices
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On the atomic interdiffusion in Co/Pt super-lattices X. Yan and T. Egami Department of Materials Science and Engineering, and Laboratory for Research on the Structure of Matter, The University of Pennsylvania, Philadelphia, Pennsylvania 19104-6272
E. E. Marinero, R. F. C. Farrow, and C. H. Lee IBM Almaden Research Center, San Jose, California 95120-6099 (Received 12 August 1991; accepted 3 February 1992)
We have performed x-ray diffraction experiments on MBE grown (111) and (001) oriented Co (3 A)/Pt (18 A) superlattices with the scattering vector Q covering a plane that includes a major component perpendicular and a minor component parallel to the plane of the sample. The superlattice diffraction peaks were found to have a large width parallel to the plane of the film, indicating that there is strong in-plane disorder. These broad peaks were integrated to evaluate more accurately the amount of interdiffusion at the interface, which was found to be similar in both films, contrary to what the conventional x-ray diffraction experiment suggests.
In an effort to understand the origin of the perpendicular anisotropy in Co/Pt superlattices, Lee et al.1 have shown for the first time, utilizing seeded epitaxial growth, that perpendicular anisotropy is controlled by the growth orientation of the superlattice. Superlattices grown by molecular beam epitaxy (MBE) show that the magnetic easy axis is perpendicular to the film plane for samples epitaxially grown on GaAs substrate with (111) orientation, whereas those with (001) orientation exhibit large in-plane anisotropy. Through studies of conventional low angle x-ray diffraction, high resolution transmission microscopy, and in situ x-ray photoelectron diffraction, atomic density profiles were deduced. A large width of the density profile suggests a sizable atomic interdiffusion, or intermixing at the interfaces, created during the growth at the Co/Pt interface.2 This may imply the formation of an interfacial CoPt alloy. The interdiffusion which was apparently more significant in the (111) sample than the (001) specimen was further suggested to contribute to the perpendicular magnetic anisotropy in the (111) oriented sample.3 However, analysis of the density profiles using conventional x-ray diffraction assumes that the intensity reduction with increasing angle (or Qz) due to imperfection is dominated by atomic interdiffusion. This does not account for the influence of the in-plane disorder, such as interfacial roughness or defects, that could significantly alter the diffracted intensity in this type of experiment. Specifically, the effect of the interfacial roughness in nonideal multilayers creates diffused intensity4 which is not included in the conventional density profile analysis. Thus the determination of the interdiffusion from the J. Mater. Res., Vol. 7, No. 6, Jun 1992
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density profile without evaluating the effect of in-plane disorder tends to overestimate the width of the density profile. In the present x-ra
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