Surface magneto-optic Kerr effect study in ultrathin Co/Ge(1 1 1) and Co/Ge(1 0 0) films

Surface magneto-optic Kerr effect has been used to study the ultrathin Co/Ge(1 1 1) and Co/Ge(1 0 0) films with the substrate temperature varying from 120 to 400 K. Three magnetic phases have been resolved. As the substrate temperature increases from 200 to 400 K, the thickness of the total nonferromagnetic layer increases from 5 to 22 monolayers for Co/Ge(1 0 0) films. Below 300 K, a thinner compound layer was formed for the Co/Ge(1 1 1) systems. This is due to the looseness of the Ge(1 0 0) surface, which gives a more opportunity for a higher concentration of cobalt atoms into the substrate to form Co–Ge compounds. However, above 400 K, our experimental data suggests that the order structure of Co layers will enhance the interaction between Co and Ge substrate.