Mössbauer-effect studies of multilayers and interfaces

The usefulness of Mössbauer spectroscopy for the investigation of magnetic multilayer systems is described. By applying 57Fe Mössbauer spectroscopy, the behavior of ultrathin magnetic layers, such as FCC-like Fe films on Cu(0 0 1), is studied. Position-specified (depth-selective) information is available by preparing samples in which monatomic 57Fe probe layers are placed at specific vertical positions, e.g. at interfaces or at the surface. As demonstrated for epitaxial chemically ordered Fe 50Pt 50 alloy films and polycrystalline nanostructured Tb/Fe multilayers, the Fe-spin structure can be determined directly, and a site-selective Fe-specific magnetic hysteresis loop can be traced in very-high-coercivity materials. For the studies of non-magnetic layers, on the other hand, hyperfine field observations by 197Au and 119Sn probes are worthwhile. Spin polarizations in Au layers penetrating from neighboring ferromagnetic 3D layers are estimated 197Au from Mössbauer spectra and are also studied by inserted 119Sn probes in Au/3D multilayers. In the Sn spectra for Cr/Sn multilayers, it was found that remarkably large spin polarization is penetrating into Sn layers from a contacting Cr layer, which suggests that Cr atoms in the surface layer have a ferromagnetic alignment.