A. Chaiken and R.P. Michel
Materials Science and Technology Division
Lawrence Livermore National Lab
Livermore, CA 94551
Department of Materials Science and Engineering
Palo Alto, CA 94305
Fe/Si multilayers with antiferromagnetic interlayer coupling have been grown via ion-beam sputtering on both glass and single-crystal substrates. High-angle x-ray diffraction measurements show that both sets of films have narrow Fe peaks, implying a large crystallite size and crystalline iron silicide spacer layers. Low-angle x-ray diffraction measurements show that films grown on glass have rougher interfaces than those grown on single-crystal substrates. The multilayers grown on glass have a larger remanent magnetization than the multilayers grown on single-crystal substrates. The observation of magnetocrystalline anisotropy in hysteresis loops and (hkl) peaks in x-ray diffraction demonstrates that the films grown on MgO and Ge are epitaxial. The smaller remanent magnetization in Fe/Si multilayers with better layering suggests that the remanence is not an intrinsic property.
The well-established picture of antiferromagnetic coupling in metal/metal multilayers would have to be extensively modified for coupling across insulating or semiconducting spacer layers, where the spacer does not possess a Fermi surface.[1,2] In particular the temperature dependence of the exchange coupling might be significantly different in ferromagnet/semiconductor multilayers where the exchange is mediated by thermally activated carriers.
Unusual temperature-dependent magnetic properties have been reported for Fe/Si multilayers. For example, a large increase in the remanent magnetization has been observed at low-temperature. If the interlayer antiferromagnetic (AF) coupling increases with decreasing temperature, as in multilayers with metal spacers, one might expect the remanence instead to decrease at low temperature. Proper interpretation of the remanent magnetization in Fe/Si multilayers may therefore be important to understanding the origin of the interlayer coupling in this system. One way to explore the origin of the remanence is to compare films of different crystalline quality.