Inverse And Normal Tunneling Magnetoresistance Effects In Fecogd/Feco/Alo/Feco Multilayers

FeCoGd/FeCo(t)/AlO/FeCo magnetic tunnel junctions were fabricated with a very thin FeCo layer inserted between the FeCoGd layer and the AlO barrier. At room temperature, inverse tunneling magnetoresistance (TMR) effect and normal TMR effect were observed simultaneously in the low and high magnetic field regions, respectively. The absolute values of both inverse and normal TMR ratios, the saturation magnetic field corresponding to the normal TMR effect have similar dependence on t. Transmission electron microscopy studies indicate that a thin granular film is likely formed between the FeCoGd layer and the AlO barrier, which may result in the normal TMR effect at high magnetic fields.