Shot noise and tunneling magnetoresistance in disordered MgO-based double-barrier magnetic tunnel junctions: First-principles study

摘要

We report first-principles study of shot noise and tunneling magnetoresistance in Fe/MgO/Fe- /MgO/Fe double-barrier magnetic tunnel junctions (MTJs). We mainly investigate the effects of disordered interfacial oxygen vacancies and barrier asymmetry on the spin-dependent tunneling. It is found that interchannel scattering induced by interfacial oxygen vacancies can substantially enhance the tunneling conductance of the antiparallel magnetic configurations, and results in the dramatic decrease of tunneling magnetoresistance. Moreover, we find the interfacial disorder scattering favors the sub-Poissonian tunneling process. As a result, Fano factors of symmetric MTJs maintain at around 0.5, or are suppressed, while Fano factors of asymmetric MTJs can all be significantly suppressed, illustrating the important correlations in tunneling induced by interfacial disorders. Interchannel scattering induced by interfacial oxygen vacancies can effectively couple the electron to high-transmission channels, enhancing the transmission and reducing the shot noise. In comparison with interfacial disorder, middle-layer disordered Fe vacancies present limited modulation on the Fano factor. Increasing the asymmetry of barriers can quickly decrease high-transmission channels, and make the tunneling process Poissonian in double-barrier MTJs.