  Current-induced motion of domain walls (CIMDW) with interfacial
Dzyaloshinskii-Moriya interaction (DMI) in heavy metal (HM)/ferromagnetic (FM)
metal multilayers have attracted attention owing to their potential application
in novel magnetic memories. In recent years, the CIMDW at ultrahigh speed has
been observed in a synthetic antiferromagnetic (SAF) multilayer. However, due
to the zero net magnetization, the reading of information from the SAF
multilayer is still challenging. In this work, we propose a readable racetrack
memory consisting of a synthetic ferromagnetic multilayer composed of two FM
layers with an interlayer FM coupling. One FM layer had an isotropic DMI, while
the other had an anisotropic DMI. This difference of DMIs resulted in the
opposite tilting directions of the DW planes in the two layers. This tilting
was inhibited by a strong interlayer FM coupling, resulting in an increase in
the DW velocity and the reduction of the minimum allowed spacing between two
adjacent DWs. In addition, the FM coupling enhanced the stray field, and the
stored information could be read conveniently using a conventional reading
head. Therefore, our proposal paves a way for the fabrication of a racetrack
memory with high reading speed, large storage density, and good readability.
