Properties of exchange biased Co/Co3O4 bilayer films

Co/Co₃O₄ bilayer films were fabricated by RF sputtering with Co and Co₃O₄ targets. Exchange bias effect in the bilayer films was observed at 80 K by vibrating sample magnetometer. The bias effect disappeared about 240 K slightly lower than the Néel point of CoO and much higher than the Néel temperature of Co₃O₄ about 40 K. To clarify the origin of the exchange bias effect, Auger and X-ray photoelectron spectroscopy were employed and CoO was found at a transition region from Co₃O₄ layer to Co layer due to oxygen diffusion during sputtering. The angular dependence of exchange bias field H_E was obtained to obey function of H_E(θ)=18.06 (kA/m)[−cos θ+0.22 cos 3θ+0.03 cos 5θ−0.01 cos 7θ+].