Magnetic properties of ultrathin cobalt films grown on Ge(111) and Si(111) substrates

Magnetic properties of cobalt films grown on Ge(111) and Si(111) substrates were investigated. On a Ge(111) substrate, cobalt films possess an in-plane anisotropy. On a Si(111) substrate, ultrathin cobalt films (3-9 monolayers), which were deposited at 300 K, exhibited a canted easy axis. The different orientations of the easy axis of magnetizations are attributed to the different roughness of the film/substrate interfaces. Interaction between Co layers and the substrates produces intermixed compound layers that are nonmagnetic. The thickness of this compound layer is 3.8 monolayers for Co/Ge(111), and 2.1 monolayers for Co/Si(111). A series of annealing experiments showed that the onset temperature of the disappearance of the magnetism for Co films is lower on Ge than that on Si substrate. For cobalt film, this onset temperature is 300 K on Ge(111) and 575 K on Si(111).