An extensive study of the growth of Fe/Si multilayers by ion-beam sputtering has been performed. The crystalline quality of the films is better when they are grown with thick Fe layers, with thin Si layers, at high temperature, and on single-crystal substrates. Improved growth conditions lead to higher saturation fields and lower remanence in magnetization curves. Measured bilayer periods are consistently shorter in these multilayers than the nominal value, suggesting formation of a dense silicide phase in the spacer layer. Despite considerable interdiffusion in the multilayers, a strong composition modulation along the growth direction is maintained as evidenced by SAXS measurements.
There are two surprising results from this study. One is that the films grow on glass with a mixed (011) and (001) texture near nominal RT and with a pure (011) texture at higher and lower temperatures. The other surprise is that the strength of the interlayer coupling depends strongly on the number of bilayer periods in films with thin Fe layers. This latter result is explained on the basis of substrate surface roughness.
Unraveling the behavior of the Fe/Si multilayer system has proven to be a considerably more complex task than understanding the Fe/Cr or Co/Cu multilayer systems. The reason is that compound formation at the Fe/Si interface is crucial to understanding the AF interlayer coupling. Identification of possibly disordered phases in the spacer layer of a multilayer continues to be an experimental challenge. Mounting evidence suggests that the spacer layer in the AF-coupled Fe/Si multilayers is metallic and crystalline and that the Fe/Si interlayer coupling therefore has the same origin as in metal/metal multilayers.
We would like to thank P.E.A. Turchi, T.W. Barbee Jr., T.P. Weihs, E.E. Fullerton, Y. Huai and E.C. Honea for helpful discussions, and B.H. O'Dell and S. Torres for technical assistance. Further thanks go to C.-T. Wang of Stanford for the four-circle x-ray diffractometry and to Sandia National Lab for use of their electron microscope for HREM work. Part of this work was performed under the auspices of the U.S. Department of Energy by LLNL under contract No. W-7405-ENG-48.