Magnetic and structural properties of thin Fe films grown on Ni/Si

Fe films ranging in thickness from 6 to 90 {} have been prepared on Ni layers with constant thickness of 140 {} 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-energy 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 {≤}32 {}, the average magnetic Fe moments come out to be very low around 0.2μB. For Fe layers {≥}60 {}, 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 fcc-like to bcc with increasing Fe layer thickness. Fe films below 32 {} 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.