Application of High-Resolution Electron Microscopy to the Study of Magnetic Thin Films and Multilayers
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APPLICATION OF HIGH-RESOLUTION ELECTRON MICROSCOPY TO THE STUDY OF MAGNETIC THIN FILMS AND MULTILAYERS R. Sinclair, T.P. Nolan, G.A. Bertero and M.R. Visokay Department of Materials Science and Engineering, Stanford University, Stanford CA, 94305
ABSTRACT The performance of a wide range of modem magnetic thin-film materials for information storage is found to depend dramatically on grain nucleation and coherence at interfaces. Three such systems, Fe/Pt multilayers, Co/Pt multilayers, and CoCrTa/Cr bilayers are considered here. High-resolution electron microscopy (HREM) shows that ordered CoPt and FePt Lio structures can be formed and oriented, using coherence with the substrate, with their magnetically easy c-axes perpendicular to the film plane. This orientation results in the perpendicular magnetization required for magneto-optic recording media. Different sputtering gases used in producing Co/Pt multilayers result in varying degrees of interfacial intermixing, which is shown to strongly affect the perpendicular magnetic anisotropy energy. The required high in-plane coercivity of longitudinal recording media is also correlated with the observed interface coherence and the resulting oriented growth of CoCrTa with the magnetically hard axis perpendicular to the film plane. Many features of the microstructure can be observed directly at the atomic level by HREM, and so the usefulness of this technique is emphasized in this paper.
INTRODUCTION The microstructural components which make up contemporary magnetic thin films are rapidly approaching the atomic level. For example magnetic multilayers may be comprised of metal films only a few monolayers thick. The crystal sizes of recording media are often 10-20 nm in lateral dimension. Accordingly the interface structure plays an important role in determining the properties, and higher resolution techniques are required to study the important microstructural features. High-resolution electron microscopy (HREM) can now reveal atomic arrangements even in close-packed metals and so is well-suited to this endeavor. This paper describes some of our recent work using HREM, drawing on examples from multilayer systems (e.g., Co/Pt, Fe/Pt) and from longitudinal recording media (e.g. CoCrTa alloy).
EXPERIMENTAL PROCEDURE The magnetic thin films were made by sputtering techniques. They are examined in crosssection and through-foil geometries in a Philips EM430 (300 kV) transmission electron microscope which has about 0.19 nm resolution. Additional characterization is performed using standard bright and dark field imaging, selected area and microdiffraction, elongated probe microdiffraction and x-ray energy dispersive microanalysis [1]. Bulk studies are also carried out by x-ray diffraction, vibrating sample magnetometry, magneto-optic Kerr rotation and torque magnetometry. Mat. Res. Soc. Symp. Proc. Vol. 313. ©1993 Materials Research Society
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RESULTS CoPt and FePt (001) Annealed Films There has been significant interest lately in magnetic alloys with perpendicular magnetic a
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