  Nanoscale CoFeB amorphous films have been synthesized on GaAs(100) and
studied with X-ray magnetic circular dichroism (XMCD) and transmission electron
microscopy (TEM). We have found that the ratios of the orbital to spin magnetic
moments of both the Co and Fe in the ultrathin amorphous film have been
enhanced by more than 300% compared with those of the bulk crystalline Co and
Fe, and in specifically, a large orbital moment of 0.56*10^-6 B from the Co
atoms has been observed and at the same time the spin moment of the Co atoms
remains comparable to that of the bulk hcp Co. The results indicate that the
large uniaxial magnetic anisotropy (UMA) observed in the ultrathin CoFeB film
on GaAs(100) is related to the enhanced spin-orbital coupling of the Co atoms
in the CoFeB. This work offers experimental evidences of the correlation
between the UMA and the elementary specific spin and orbital moments in the
CoFeB amorphous film on the GaAs(100) substrate, which is significant for
spintronics applications.
