Co1-xMnx thin films epitaxially grown on GaAs(001) have been studied using
reflection high-energy electron diffraction, x-ray diffraction, and the mag
neto-optical Kerr effect. The result shows that Co-rich films are body-cent
ered cubic and ferromagnetic, and Mn-rich ones are face-centered cubic and
antiferromagnetic. However, the film structure and magnetism at x similar t
o0.5 show strongly thickness-dependent behavior. The magnetic phases of ord
ered Co1-xMnx alloys (x = 0,1/4,1/2,3/4,1) in both bcc and fcc structures h
ave also been investigated by a first-principles linearized augmented plane
-wave calculation in the local-spin-density approximation. With the help of
the calculated results, the correlation established in experiment between
the structure and magnetism of Co1-xMnx alloys is better understood.