MAGNETIC AND STRUCTURAL-PROPERTIES OF THIN FE FILMS GROWN ON NI SI/

Fe films ranging in thickness from 6 to 90 Angstrom have been prepared on Ni layers with constant thickness of 140 Angstrom grown on Si(100) in ultrahigh vacuum. Magnetic properties have been studied by spin-po larized neutron reflection and superconducting quantum interference de vice magnetometry and structural properties have been investigated by small-angle x-ray reflectometry and reflection high-enegy electron dif fraction. As the main result of this work it is shown that the magneti c states of the Fe films strongly depend on their thicknesses. For Fe layers less than or equal to 32 Angstrom, the average magnetic Fe mome nts come out to be very low around 0.2 mu(B). For Fe layers greater th an or equal to 60 Angstrom, the Fe moments increase by a factor of abo ut 10 close to the value known for bulk iron. Most probably these chan ges can be attributed to a structural phase transition of the Fe films from fee-like to bce with increasing Fe layer thickness. Fe films bel ow 32 Angstrom are either antiferromagnetic or exhibit almost vanishin g Fe moments. The discussion includes a comparison of our results for Fe/Ni bilayers with results published for Fe/Ni multilayers and for Fe films on Cu.