Resonant enhancement of thermal spin-transfer torque in asymmetric double-barrier tunnel junctions

Charge current and thermal spin-transfer torque (TSTT) in asymmetric double-barrier magnetic tunnel junctions (DBMTJs) with a non-magnetic metal (NM) spacer as CoFeB/MgO/NM/MgO/LSMO are studied by non-equilibrium Green's function (NEGF) formalism. It is found that the results show oscillatory behavior with an increase of the NM spacer thickness due to the resonant tunneling effect through the DBMTJs structures. About the dependence of the temperature difference and angle between the magnetizations, the charge current and TSTT are larger at the specific thicknesses (resonant positions) of the NM spacer than the others. The results also illustrate a magnitude enhancement for asymmetric DBMTJs compared with asymmetric single-barrier MTJs (SBMTJs). Therefore, it is possible to achieve a large TSTT for magnetization dynamics by new asymmetric DBMTJs.