Magnetic properties of ultrathin Co/Ge (111) film with oxygen surfactant

Magnetic properties of ultrathin CoGe (111) films with oxygen surfactant have been investigated using surface magneto-optic Kerr effect technique. As the oxygen exposure increases, their magnetic properties could be significantly modified. As the thickness of Co films increases to above 6 ML (monolayer), pure cobalt islands start to accumulate on the surface and the amount of oxygen on the surface layers increases with increasing oxygen exposure time. Series experiments of different sequences of oxygen exposure and Co deposition have been performed. From the results of slight chemical shift and depth profiling measurements, one can conclude that oxygen plays a role as a surfactant. The adsorbed oxygen influences the electronic density of states of Co and leads to the changes of the magnetic properties. The appearance of the OCoGe interface could modify the stress anisotropy, and as a result the coercivity of 30 ML CoGe (111) increases from 730 to 810 Oe with 500 L of oxygen exposure.