Spin transfer torque-based magnetic random access memory with perpendicular magnetic anisotropy (PMA) provides better scalability and lower power consumption compared to those with in-plane anisotropy. Spin transfer torque switching in magnetoresistive spin valves with PMA is investigated. The hard layer is made of (Co/Pd) multilayer, whereas the soft layer is a lamination of (CoFe/Pd) and (Co/Pd). By the insertion of an in-plane spin polarizer adjacent to the perpendicular anisotropy free layer, thus creating a modified-dual spin valve, a significant reduction of about 40% in the current density required for spin torque transfer switching was observed. By using a spin polarized current with different pulse widths down to 10 ns, the barrier energy EB in 100-nm-diameter devices was found to be reduced from 1.1 to 0.43 eV. Besides the reduction of switching current density in a device with PMA, the new structure shows a clear increase in magnetization switching speed as revealed by micromagnetic simulation.

We have studied spin transfer switching (STS) in a magnetic tunnel junction with perpendicular magnetic anisotropy for the reference and free layers using the Landau–Lifshitz–Gilbert formalism. We propose a multilayer structure in which the insertion of an additional spin polarizer with in-plane anisotropy can enhance the STS efficiency and switching speed of the device. It is revealed that a canted spin polarizer with an angle between 40° and 80° out of the film plane in the correct direction enhances the STS efficiency more than a fixed in-plane or perpendicular polarizer. Furthermore, we show that the spin transfer torque exerted on the in-plane polarizer layer by the free layer automatically tilts the in-plane polarizer in the direction that enhances STS for both magnetization states of the free layer.

We have studied the switching characteristics and magnetoresistance of pseudo-spin-valves with perpendicular anisotropy based on CoFe∕Pd multilayers. In unpatterned thin films without exchange biasing, a maximum current-in-plane giant magnetoresistance of 7% was achieved, the highest reported to date in perpendicular pseudo-spin-valves. A Ta seed layer and the fcc (111) orientation of Pd was shown to be important in order to achieve good perpendicular anisotropy and sharp switching behavior. The improvement in perpendicular anisotropy and decay in magnetoresistance upon postdeposition annealing have been attributed to the formation of CoPd alloys at the CoFe∕Pd interfaces.

A novel multi-bit dual pseudo spin valve with perpendicular magnetic anisotropy is investigated for spin transfer torque (STT) switching. The structure consists of two free layers and one reference layer, and all are based on Co/Pd multilayer. STT switching of the multi-bit device shows distinct four resistance levels. The selection of intrinsic properties of each ferromagnetic layer can be controlled for distinct separation of the resistance levels as well as the respective STT switching current. Reversible transitions between different states can be achieved by a pulsed current, in which its critical value is found to be linearly dependent on pulse duration.