Inelastic electron tunneling spectrum from surface magnon and magnetic impurity scatterings in magnetic tunnel junctions

Abstract

Analytic expressions for contributions to the inelastic electron tunneling spectrum ͑IETS͒ from surface magnon scattering and magnetic impurity scattering are obtained. It is shown that surface magnon scattering alone does not lead to peaks in the IETS. The peaks at small bias often observed in the IETS of magnetic junctions are due to magnetic impurity scattering, in agreement with the traditional model for zero-bias anomaly. These impurity resonance peaks can sometimes split due to the impurities' magnetic coupling to the electrodes. Measurements of AlO and MgO barrier junctions yield excellent agreement to the theory. The experiment further shows that the magnetic impurities in MgO barriers are strongly coupled to the electrodes but those in AlO barriers are not magnetically coupled to the electrodes.

Symmetry-dependent electron-electron interaction in coherent tunnel junctions resolved by measurements of zero-bias anomaly

“…Here, E 0 = 100 mV is used according to Ref. [37], and G 3 , G 2 , and T fit are the fitting parameters. Moreover, in the range 1 > E/kT > 0.1, the fitting curves are always slightly higher than the experimental data.…”

“…In IETS of MTJs [29][30][31][32][33], the ZB peak has been ascribed to various mechanisms, including magnon excitation [34], magnetic impurity scattering [35], and a combination of magnon scattering and EEI [27]. Although some earlier works [25,36] did not distinguish between ZBA and magnon-induced reduction of TMR over a much wider bias range, it was later shown theoretically that interface magnon scattering does not yield sharp peaks at all [37], contradicting the interpretation that the ZBA and the sharp peak in the IETS near zero bias are due to magnon excitation. More importantly, there have been suggestions that the ZBA may be due to EEI [27,28], but conclusive evidence is lacking.…”

Tunneling behavior in ion-assist ion-beam sputtered CoFe/MgO/NiFe magnetic tunnel junctions

“…present within the barrier. These channels lead to inelastic hopping via chains of localized states (LS), and have been explored previously [6][7][8][9][10].…”

Evidence for magnon excitation contribution to the magnetoresistance behavior during thermal annealing in CoFeB/MgO/CoFeB magnetic tunnel junctions

“…The details of sample growth, junction fabrication, and measurement setup can be found elsewhere. 13,[24][25][26][27] Figure 1 shows the MR ratio [(R AP /R P − 1) × 100%] measured at room temperature (RT) as a function of annealing temperature T a , similar to the results reported before, 11,12 where R AP,P stand for the resistance in the antiparallel (AP) and parallel (P) configurations, respectively. The MR ratio increases gradually as T a is first increased, and then it dramatically increases when T a > 300 • C. It reaches a maximum at 375 • C, and then decreases with further increasing T a , resulting in a peak (the peak temperature is called T p ).…”

“…[16][17][18][19][20][21][22][23][24] Using this method, the influence of the density of states (DOS) and the inelastic scattering process on conductance can be clarified by measuring the first and second derivative of conductance. 24,25 Here, we report a detailed investigation of the dynamic conductance and IET spectra in CoFeB/MgO/CoFeB junctions as a function of annealing temperature T a , with a focus on the magnetoresistance (MR) behavior. Our results show that magnon excitation contributes greatly to the annealing-temperature-dependent MR behavior.…”