Abstract
For sputteredCoFeB/MgO/CoFeB magnetic tunnel junctions, it is well known that the tunnelmagnetoresistance (TMR) ratio increases with increasing annealing temperature (Ta) up to a critical value (Tp), and then decreases with further increasing Ta , resulting in a peak around Tp. The improved crystallinity of the MgO barrier and CoFeB electrodes due to annealing has been considered as the main reason for the enhancement of the TMR ratio, especially for Ta < Tp. In this work, the evidence is provided that the magnon excitation plays a great contribution to the magnetoresistance (MR) behavior in annealed samples based on the measurement of dynamic conductance and inelastic electron tunneling (IET) spectra. The magnon activation energy (Ec) obtained from the fits for IET spectra exhibits a similar temperature dependence with that of the TMR ratio. A detailed analysis shows that the magnon excitation, together with improved crystallinity of the MgO barrier and CoFeB layers, is the main contribution to the annealing-temperature-dependent MR behavior.