Ferromagnetism of CoAl(100) induced by oxidation at 300 K

In situ magneto-optical Kerr effect measurements were performed to investigate the magnetic behavior of CoAl(100) upon oxidation at room temperature. As an ideal Co$_{50}$Al$_{50}$ crystal is known to be paramagnetic at room temperature, our studies show a transformation into a ferromagnetic phase during increasing exposure to O$_{2}$. Oxidation of CoAl(100) at 300 K leads to the growth of an amorphous Al$_{2}$O$_{3}$ film [1], causing a Co excess at the metal/oxide interface that is sufficient to provide ferromagnetism. Annealing of the oxidized sample brings about a drastic increase of the coercive field, generated by diffusion of Al into the Co film. But, after annealing at 550 K, the ferromagnetism vanishes completely. [1] V. Rose, V. Podgurski, I. Costina, R. Franchy, Surf. Sci 541 (2003) 128.