Non-epitaxial, Highly Textured (001) CoPt:B 2 O 3 Composite Films for Perpendicular Recording
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Non-epitaxial, Highly Textured (001) CoPt:B2O3 Composite Films for Perpendicular Recording M. L. Yan, N. Powers and D. J. Sellmyer Center for Materials Research and Analysis and Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska 68588-0113 ABSTRACT We report the non-epitaxial growth of highly textured (001) CoPt:B2O3 nanocomposite thin films that are deposited directly on thermally-oxidized Si wafers. Multilayers of Co/Pt/Co/B2O3 are deposited followed by appropriate thermal processing. The as-deposited films are disordered fcc CoPt phase, and magnetically soft. After annealing, an (001) orientation of CoPt-ordered grains is developed. The texture development is dependent both on the total film thickness and the annealing process. Nearly perfect (001) texture can be obtained in films with thinner initial layer thicknesses. Strong perpendicular anisotropy is shown to be related to this (001) texture. INTRODUCTION L10 FePt and CoPt-based composite films prepared by sputtering are promising materials for extremely high-density recording media because of their high magnetic anisotropy. Usually, fct ordered FePt and CoPt films have (111) preferred or random orientations under normal growth conditions, which is similar to fcc-structured films. For magnetic recording applications, it is desirable for the easy axis of magnetization in the films to orient either in the film plane or perpendicular to the plane. Hence, CoPt or FePt-based films should be (110) textured ( grains are aligned parallel to the film plane) if the films are used as longitudinal recording media, or (001) textured ( grains are aligned perpendicular to the film plane) if the films are used as perpendicular recording media. Normally, such texture can be obtained by epitaxal growth on heated single crystal-substrates.1 For example, MgO(100) substrates were used for film deposition in order to create epitaxially-grown CoPt or FePt grains and to obtain (001) texture. For practical purposes, it is useful to explore new methods to obtain such textured films. Only most recently has it been possible to achieve both (001) and (110) texture for FePt-based nanocomposite films,2-4 and (001) texture for CoPt-based nanocomposite films.5-6 The texture is sensitive to many factors, including the as-deposited multilayer structure. The mechanism of texture formation, however, still remains mostly unclear. In this study, we investigate the evolution of the texture of CoPt:B2O3 composite films with different total film thicknesses and annealing processes in order to understand the texture formation mechanism, and to assist the design of nanocomposite films with a desired texture. EXPERIMENT The samples were magnetron sputtered on thermally oxidized Si substrates with a multilayer structure of [Co/Pt/Co/B2O3]n. The composition of Co, Pt and B2O3 was well controlled by adjusting the thickness ratio of Co, Pt and B2O3 layers. The total film thickness was varied by adjusting n. The purpose of the B2O3 was to serve as a non-magnetic matrix, reducing t
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