Magnetic Properties of Epitaxial 6 ML fcc-Fe/Cu(100) Films
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MAGNETIC PROPERTIES OF EPITAXIAL 6 ML fcc-Fe/Cu(100) FILMS
L. J. Swartzendruber, L. H. Bennett, M.T. Kief, and W. F. Egelhoff, Jr. National Institute of Standards and Technology Gaithersburg, MD 20899 ABSTRACT A study has been made of the magnetic properties of epitaxial 6 monolayer (ML) fcc-Fe films on Cu(1 00) with various thicknesses of epitaxial Cu deposited on top of the Fe. It was found that the magnetic properties undergo striking changes as a function of the Cu thickness. The easy axis of magnetization goes from being in-plane for the bare Fe to perpendicular upon the deposition of 1 ML Cu. Concurrently there is a dramatic decrease inthe Kerr signal intensity at saturation. Upon depositing a second ML of Cu the Kerr signal intensity more than doubles, and the easy axis remains perpendicular. For Cu overlayers of 3 ML to 10 ML the Kerr signal intensity at saturation gradually diminishes to below the level of detectability, as ifthe Fe were nonmagnetic. A superlattice consisting of 60 ML Cu/(6 ML 57Fe/ 10 ML Cu)x5/Cu(100) was fabricated and studied at room temperature by conversion electron M6ssbauer spectroscopy. The results confirmed that the Fe is indeed nonmagnetic. The four inner Fe layers of the 6 ML film have the same isomer shift as bulk fcc-Fe in precipitates inCu, and the two boundary Fe layers exhibit an asymmetric quadrupole doublet. INTRODUCTION The study of ultrathin films of fcc-Fe on Cu(1 00) has been the subject of much interest and some controversy in recent years.[1 -10] Such films have served as a testing ground for theories of epitaxial growth and of fundamental magnetic interactions.[1-10] These films are also of interest as building blocks for nanocomposite materials consisting of epitaxially-grown layered structures which exhibit novel and technologically important properties such as the giant magnetoresistance effect.[1 1] There are several reasons for interest in novel materials based on the Fe-Cu system. First, Fe and Cu have low solubilities in one another, implying greater thermal stability with respect to interdiffusion than would be the case for structures of, say, Ni-Cu which are miscible. Second, the excellent lattice match between fcc-Fe and Cu means that structures with coherent interfaces may readily be grown. Third, small fcc-Fe atom clusters (2 - 10 atoms) inCu have a large moment, and this effect is often manifested in ultrathin epitaxial films of fcc-Fe. Fourth, an enhancement of a factor-of-two in the Kerr rotation (important for magneto-optical data storage applications) have been found for the Fe/Cu system due to coupling of the photon with the plasma edge of the Cu.[12] Afurther enhancement is associated with an exchange interaction in Fe/Cu/Fe structures.[9] EXPERIMENTAL The molecular beam epitaxy system in which the samples were grown has been described in previous publications.[13-15] Briefly, it consists of a growth chamber which operates inthe 10-10 torr range and is equipped with four K-cells, Mat. Res. Soc. Symp. Proc. Vol. 313. 1 1993 Materials Research Soc
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