Structural and magnetic properties of La/Fe multilayers

The structural and magnetic properties of La/Fe multilayers were investigated by X-ray diffraction, RHEED, magnetometry and Fe-57 Mossbauer spectroscopy. Comparison is made with previous results obtained for Ce/Fe multilayers. Remarkably sharp interfaces are found, with roughness between 2 and 2.5 Angstrom. The magnetic interface in the Fe sublayers resulting from the distribution of magnetic hyperfine fields distinctly exceeds the extension of the structural interface and points to a magnetic proximity effect. This is discussed in relation to a strong 3d-5d hybridization recently found in measurements of magnetic circular X-ray dichroism. Both the structural and magnetic La/Fe interface is less extended than the interface in Ce/Fe multilayers. Below a thickness of about 25 Angstrom, the individual Fe layers grow in an amorphous structure on the La layers. In this case, Curie temperatures are below 200 K and the Fe-layer saturation magnetization is reduced up to 50%, and there is evidence of a non-collinear spin structure. It is argued that this mainly reflects the properties of pure amorphous Fe.