Effect of quantum confinement on spin transport and magnetization dynamics in dual barrier spin transfer torque magnetic tunnel junctions

摘要

Electronic transport and magnetization dynamics associated with the current induced spin torque effects in dual barrier magnetic tunnel junctions (MTJs) have been investigated using nonequilibrium Green's Function equations solved self-consistently with Landau-Lifshitz-Gilbert-Slonczewski equation. In a dual barrier (pentalayer) MTJ, a set of geometry and band-structure parameters jointly determines the position of resonant peaks and valleys within the energy range of interest. The presence of nonmonotonic quantum well states inside the central ferromagnetic free layer significantly modifies the critical switching voltage across MTJ and tunneling magnetoresistance simultaneously depending on whether the resonant condition is satisfied. Proper choice of (i) free ferromagnetic layer thickness, (ii) tunneling barrier height, (iii) width of the tunneling barrier, and (iv) operational voltage has been found to increase both in-plane and out-of-plane spin torque efficiencies in pentalayer MTJs by approximately an order in magnitude as compared to the conventional single barrier trilayer structures. Transport simulation results are in a reasonable quantitative agreement with the existing set of trilayer MTJ experiments. Energy efficiency of pentalayer MTJ structures over that of trilayers during spin torque driven magnetization switching has also been reported quantitatively under resonance conditions.