Magnetoresistance and electronic structure of granular films with MgO or MgF2 matrices

The magneto-transport properties and electronic structures of FeCo-MgO, FeCoB-MgO, FeCo-MgF2 and FeCoB-MgF2 granular films were investigated. From the X-ray photoelectron spectroscopy (XPS) measurements, it was recognized that the oxide layer formed on the surface of granules in FeCo-MgO. Especially Fe oxides were preferentially formed. By using (Fe50Co50)(80)B-20, the formation of Fe oxides on the granule surface was suppressed since B was oxidized instead of Fe. The MR ratio of FeCoB-MgO was approximately 2%. By using MgF2 matrix, the surface states of granules were drastically improved. XPS measurements indicated that an amount of metallic Fe in FeCoB-MgF2 increased compared with FeCoB-MgO. Reflecting the improvement of surface states of granules, a large MR ratio of approximately 6 % was obtained in FeCoB-MgF2.