Controlling shot noise in double-barrier magnetic tunnel junctions

Shot noise of spin-polarized electrons in a single-channel magnetic tunnel junctions

Based on the free electron approximation and Egues' shot noise theory, the shot noise of spin-polarized electrons tunneling in ferromagnetic/semiconductor/ferromagnetic tunnel junctions is studied. Considering the matching of conduction band between ferromagnetic and semiconductor layers, our results show that the Fano factors of spin-polarized electrons have resonant tunneling characteristics when the semiconductor thickness and Rashba spin-orbit coupling strength are increased. When the magnetic moments in two ferromagnetic layers are parallel, with the increase of the molecular field in the ferromagnets, the Fano factor for spin-up electron decreases to zero and then increases exponentially and the Fano factor for spin-down electron is always linear. But when the magnetic moments are antiparallel, the Fano factors for different spin directions tend to be the same. In addition, the Fano factors for different spin directions are almost zero when the incident electron energy is located in the low energy region, but exhibit irregular oscillation when the incident electron energy is located in the high energy region. At the same time, with the variations of the angle of the magnetic moments in two ferromagnetic layers, the electrons Fano factors for different spin orientations show obvious separation characteristics. On the other hand, the conduction band mismatch between ferromagnetic and semiconductor layers is considered, the Fano factors of electrons with different spin directions show obvious difference compared with the results of conduction band matching.

Symmetry broken spin reorientation transition in epitaxial MgO/Fe/MgO layers with competing anisotropies

The observation of perpendicular magnetic anisotropy (PMA) at MgO/Fe interfaces boosted the development of spintronic devices based on ultrathin ferromagnetic layers. Yet, magnetization reversal in the standard magnetic tunnel junctions (MTJs) with competing PMA and in-plane anisotropies remains unclear. Here we report on the field induced nonvolatile broken symmetry magnetization reorientation transition from the in-plane to the perpendicular (out of plane) state at temperatures below 50 K. The samples were 10 nm thick Fe in MgO/Fe(100)/MgO as stacking components of V/MgO/Fe/MgO/Fe/Co double barrier MTJs with an area of 20 × 20 μm². Micromagnetic simulations with PMA and different second order anisotropies at the opposite Fe/MgO interfaces qualitatively reproduce the observed broken symmetry spin reorientation transition. Our findings open the possibilities to develop multistate epitaxial spintronics based on competing magnetic anisotropies.