Comparative study of the d-band filling effect on the magnetic behavior of Co _xNi _1-x and Fe _xNi _1-x ultrathin films on Cu(100)

The ultrathin Fe _xNi _1-x/Cu(100) and Co _xNi _1-x/Cu(100) alloy films with x≤10% were prepared for the study of spin-reorientation transition with precise variation of composition and coverage of the films. The spin-reorientation transition with the variation of the film coverage was observed in Co _xNi _1-x/Cu(100) with x<10% as well as Fe _xNi _1-x/Cu(100) with x<6%. This transition was found to be strongly affected by the alloy composition of the alloy films. The critical thickness for the spin-reorientation transition changes from 7.5 ML with x=0 to 17.5 ML with x=8% for Co _xNi _1-x/Cu(100). A more sensitive composition-driven effect has been found in Fe _xNi _1-x/ Cu(100) by varying the Fe concentration for the critical thickness to 16 ML with x=5%. The more drastic influence of the concentration of Fe than Co on the critical thickness of the spin-reorientation transition can be attributed to the greater deviation of the difference in 3d electron number of majority and minority bands between Fe and Ni than that between Co and Ni.