Magnon Excitation at the Interface of Co/Al/Al-Oxide/Co Tunnel Junctions

Abstract

Inelastic-electron-tunneling spectroscopy (IETS) was used to investigate the electron states of the Co/Al(d_Al)/Al-oxide/Co interface in ferromagnetic tunnel junctions. The IET spectra for both parallel and anti-parallel magnetization configurations of ferromagnetic electrodes showed a strong positive peak for d_Al = 0 Å. The subtraction spectrum defined by the difference between the spectra of the two configurations was calculated. The subtraction spectrum indicates only a magnon-assisted inelastic tunneling process. The tendency of the tunneling magnetoresistance (TMR) ratio to decrease with bias voltage agreed with the shape of the subtraction spectrum. By assuming surface magnon inelastic excitation, we obtained the distributions of correlation length and Curie temperature for both ferromagnetic electrode surfaces on the insulator. If an Al layer was inserted between a ferromagnet and an insulator, the subtraction spectrum showed an asymmetry to the bias voltage and magnon inelastic excitation at the interface decreased.