Analysis of the Interlayer in Al/Al₂O₃/Co/Al Junctions by Inelastic-Electron Tunneling-Spectroscopy

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Inelastic-Electron-Tunneling-Spectroscopy (IETS) has been applied to investigate the electron states of the interface of Al/Al₂O₃/Co(d_Co)/Al tunneling junctions. A zero-bias anomaly was observed in the conductance curve of the junction with d_Co of 2 Å and decreased with increasing d_Co. The IET spectra of these junctions showed a strong negative peak at 4 mV, corresponding to the zero- bias anomaly, while the another broad peak was observed for the junctions with d_Co ≥10Å. The peak was different in the position from that assigned to the Al-O LO phonon mode observed for Al/Al₂O₃/Al junction. From the magnetization measurement, it is confirmed that the ferromagnetic layer was formed for the junctions with d_Co ≥10 Å These results were discussed with the paramagnetic impurity and magnon assisted tunneling process.