Current-induced flip-flop of magnetization in magnetic tunnel junction with perpendicular magnetic layers and polarization-enhancement layers

We performed a micromagnetic investigation of current-induced magnetization switching in perpendicular magnetic tunnel junctions with polarization- enhancement layers. The pinned layer with a polarization-enhancement layer can be excited and eventually reverses at a current density lower than the value theoretically expected from that without a polarization-enhancement layer. The reversal results in continuous flip-flops of magnetizations as long as the current is applied. The flip-flop occurs at only one current polarity, caused by the precession amplification in polarization-enhancement layer. In order to prevent the unwanted flip-flop, the perpendicular anisotropy of the pinned layer must be severalfold larger than that of the free layer.