Magnetic moments of fcc Fe overlayers on Cu(100) and Co(100)

The magnetism of ultrathin fcc Fe overlayers on Cu(100) and Co(100) deposited at room temperature has been investigated at 110 K using magnetic circular dichroism in x-ray absorption spectroscopy (MCXD). Three regions of different magnetic behavior in dependence of the Fe thickness are distinguished in the element-specific MCXD investigation in agreement with the results of previous experiments. The Fe $3d$ magnetic spin and orbital moments are derived from the MCXD spectra by use of sum rules as a function of the Fe thicknesses. Up to 4 ML Fe the Fe spin moment is $3.0{\mu }_B$ on Co(100) and $2.8{\mu }_B$ on Cu(100) demonstrating that the whole Fe film is in a ferromagnetically ordered high-spin state. We find that between 5 and 10 ML Fe the average Fe spin moment is $1.1{\mu }_B$ on Co(100) and $0.8{\mu }_B$ on Cu(100). The surface region of the Fe films is ferromagnetically ordered on both substrates. The larger average moment on Co(100) originates from the additional contribution of the Fe atomic layer at the Fe-Co interface. For Fe thicknesses larger than 10 ML the average Fe moment increases again.