Growth, Structure and Magnetism of Cobalt-Platinum Ultrathin Films and Sandwiches
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GROWTH, STRUCTURE AND MAGNETISM OF COBALT-PLATINUM ULTRATHIN FILMS AND SANDWICHES
J.P. DEVILLE, A. BARBIER, C. BOEGLIN AND B. CARRIERE I.P.C.M.S. Groupe "Surfaces-Interfaces" - UMR 046 du CNRS 4, rue Blaise Pascal, F-67070 STRASBOURG Cedex, France
ABSTRACT Cobalt-platinum alloys and multilayers are now well known for their potentialities in magneto-optical recording media. The growth of ultrathin layers and sandwiches is thought to be useful to find the relationship between the structural and magnetic properties at an atomic level. Low Energy Electron Diffraction (LEED) and Auger spectroscopy (AES) are used here to study the crystallography and the growth modes of Pt on Co(0001) surfaces. Co/Pt/Co sandwiches are also built and investigated by the same methods. At room temperature we show the evidence of a good epitaxy of platinum on the Co(0001) surface leading to the possibility of obtaining ordered Co/Pt/Co sandwiches. Annealings at moderate temperatures lead to an epitaxial alloy formation. Auger results show that alloying indeed induces a magnetic moment on platinum atoms. This could explain the magnetic properties already observed in Co/Pt (111) multilayers. 1. INTRODUCTION In the last decade multilayers based on the Co-Pt system have become of interest as potential candidates for magneto-optical perpendicular recording media hoping to take advantage of the large magnetic anisotropy which is well known in the Li 0 structure of the PtCo alloy. This magnetic anisotropy could be due to the strong hybridation between the Co3d and Pt5d levels and the large spin-orbit coupling [1]. Lee et al. [2] have indeed studied multilayers based on this system: they concluded that the magnetic anisotropy was dependent on the growth direction and they showed that the argument given earlier by N6el [3], based on broken symmetry effects, was not sufficient to explain satisfactorily the observed magnetic anisotropies in the multilayers. More recently, multilayers based on alloys have been investigated [4,5]. They show a larger static signal level than multilayers based on the alternance of Co and Pt layers, Curie temperatures around 200°C (for Co 22Pt 78) and a good chemical stability. Annealing processes on ultrathin Pt/Co layers and sandwiches built at different temperatures allow one to get a good model to study the alloy formation and its influence on the magnetic properties of the samples. 2. EXPERIMENTAL All experiments were performed in a conventional UHV chamber with a base pressure better than 5.10-11 Torr. Auger spectra used to check the substrate cleanliness and to establish growth kinetics were obtained with a MAC2 RIBER analyzer working in the derivative mode. The LEED structural studies were done with an OMICRON Spectaleed optics allowing us to measure precise surface parameters. The cobalt single crystal surfaces were cleaned with conventional argon-ion bombardments at 300'C followed by a final annealing process at temperatures not higher than 350'C to avoid the martensitic phase transition. Platinum was then evapo
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