Analysis of the Interlayers in a Ferromagnet/Insulator Junction by Inelastic Electron-Tunneling Spectroscopy

Inelastic electron-tunneling spectroscopy (IETS) has been used to investigate the vibrational spectrum in Al/Al2O3/CO/AI tunneling junctions with various Co thicknesses (d Co). A zero-bias anomaly was observed in the conductance curve of the junction with dCo of 2Å, and decreased with increasing dCo. The IET spectra of these junctions showed strong negative peaks at 4 mV, corresponding to the zero-bias anomaly, while phonon spectra were observed for the junction with dCo ≥ 10Å. The peak position was different from that of Al/Al2O3/Al. After annealing of the junction with dCo of 2Å at 250°C for one hour, the zero-bias anomaly decreased and the phonon spectrum appeared.