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-polarized neutron reflection and superconducting quantum interference device magnetometry and structural properties have been investigated by small-angle x-ray reflectometry and reflection high-enegy electron diffraction. As the main result of this work it is shown that the magnetic states of the Fe films strongly depend on their thicknesses. For Fe layers less than or equal to 32 Angstrom, the average magnetic Fe moments come out to be very low around 0.2 mu(B). For Fe layers greater than or equal to 60 Angstrom, the Fe moments increase by a factor of about 10 close to the value known for bulk iron. Most probably these changes can be attributed to a structural phase transition of the Fe films from fee-like to bce with increasing Fe layer thickness. Fe films below 32 Angstrom are either antiferromagnetic or exhibit almost vanishing 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.