Enhancement of Thermal Spin Transfer Torque via Bandpass Energy Filtering

We propose employing the energy bandpass filtering approach in a magnetic tunnel junction device as a route to enhance the thermal spin transfer torque. Using the spin-resolved non-equilibrium Green's function formalism, we propose to harness the optical analog of anti-reflective coatings in a heterostructure MTJ device, and report a large boost in spin torque in the linear regime of temperature bias. In particular, we discuss the position of transmission function with respect to the Fermi energy that caters the maximum thermal effect. A “boxcar” transmission feature resulting from the anti-reflective configuration enhances charge and spin transport through the structure in comparison to a normal superlattice configuration. The thermally excited spin transfer torque is enhanced by almost five times with our device designs. Although, the thermally driven spin torque is much smaller than the voltage driven torque, this technique could potentially be an energy efficient way to switch the magnetization. This opens up a new viable area for spintronics applications and with the existing advanced thin-film growth technology, the optimized superlattice configurations can be achieved.