Theory of voltage-driven current and torque in magnetic tunnel junctions

We apply known relations for voltage-driven current and torque to magnetic tunneling junctions (MTJs) symmetric in composition. Postulated are effects of possibly asymmetric microstructures of the two interfaces separating the two electrodes from a barrier composed of (0 0 1)MgO. Our model takes into account effects of (i) dependence of state density on energy, (ii) possible asymmetry of the elastic transfer Hamiltonian, and tunneling enabled by inelastic mechanisms (iii) within the barrier or (iv) within the electrodes. It leads to distinct observable signatures for these effects in the voltage dependences of current and torque. A parameter-free relation connecting torque with conductance makes possible direct experimental tests of the model. Additionally, a derived formula illustrates how coulomb-correlation may contribute to these effects at high voltage.