Direct observation of magnon excitation in a ferromagnetic tunnel junctionusing inelastic-electron-tunneling spectroscopy

Inelastic-electron-tunneling spectroscopy (IETS) is applied to investigate the spin-dependent tunneling process for a Ta/Ni80Fe20/FeMn/Ni80Fe20/Al-oxi de/Co/Ni80Fe20 ferromagnetic tunnel junction. IET spec tra for ba th parall el and antiparallel magnetization configurations of ferromagnetic electrode s exhibit a strong peak at 20 mV, Using the subtraction between these spect ra, we obtain the inelastic excitation spectrum induced only by the magneti c origin. This spectrum exhibits a strong peak at 18 mV and decreases monot onically with increasing bias voltage. The bias-voltage dependence of tunne l magnetoresistance (TMR) is the same. These results are discussed by consi dering the distribution of the surface magnon excitation energy.