Effective bit addressing times for precessional switching of magnetic memory cells

Abstract

We study the effective reversal times for bit-addressed precessional switching of the magnetization in magnetic random access memories (MRAMs). In our experiments the ultrafast magnetization dynamics of the free layer of a microscopic magnetic tunnel junction cell is accessed by means of ultrafast magnetotransport. Bit-addressed switching is studied by a fast perpendicular field pulse in combination with an easy axis bias field. For vanishing effective easy axis bias fields ultrafast quasiballistic switching of the magnetization can be achieved. Furthermore the characteristic oscillatory behavior of the precessional switching under variation of the pulse duration is observed. In a certain easy axis bias field range, the so-called addressing windows, the final magnetization state after the fast pulse is always aligned with the bias field which allows reliable bit addressing in a MRAM. Also here fast magnetization switching can be obtained. However, the decay time of the remaining magnetic excitations after bit addressing strongly depends on the initial and final orientations of the magnetization. This variation leads to different effective bit addressing times for switching and nonswitching events which could limit the MRAM operation speed.