In situ observation of nano-oxide formation in magnetic thin films

In situ conductance and reflected high-energy electron diffraction (RHEED) measurements were taken during the oxidation of 20-nm-thick Co and CoFe layers. The conductance shows an initial drop with exposure to oxygen followed by a period of increasing conductance. This increase in conductance clearly indicates an increase in specular reflection of electrons at the oxide interfaces. The amount of conductance increase varied with deposition conditions. The sample with the highest increase in conductance showed an increase of 6.4×10^-4 Ω^-1 greater than the bare metal at 1.5×10^-3 Pa·s of oxygen exposure. This corresponds to a minimum increase in the specularity of 0.05. RHEED measurements show a blurring of the face centered cubic (fcc) (111) texture with exposure to oxygen, indicating the formation of an amorphous oxide during the initial conductance drop and conductance increase. After the conductance begins to fall again, a new diffraction pattern appears in the RHEED data, indicating the formation of CoO with an fcc (111) texture but with a different lattice spacing.