Current-driven magnetization switching and dynamic spin reorientation transition in magnetic tunnel junctions

We present theoretical results on electrically induced magnetization dynamics in CoFeB/MgO/CoFeB tunnel junctions connected to a constant-current source. Our calculations take into account both the spin-transfer torque (STT) created by a spin-polarized current and a voltage-controlled magnetic anisotropy (VCMA) associated with the CoFeB vertical bar MgO interface. It is shown that the current-driven spin dynamics in an ultrathin free layer of such junction is not limited by the magnetization precession and switching, but also can have the form of a dynamic spin reorientation transition, which is caused by the combined action of STT and VCMA and gives rise to a steady precessional state. Critical current densities necessary for the appearance of different types of magnetic dynamics are calculated as functions of the free-layer thickness and in-plane aspect ratio. The spin current pumped into a normal-metal overlayer by the tunnel junction with the precessing magnetization is also evaluated.