Domain wall dynamics in ferromagnet/Ru/ferromagnet stacks with a wedged spacer

Abstract

Synthetic antiferromagnetic spintronics is an important field of study in the area of spintronics. Here, we fabricate a wedged-Ru layer in a ferromagnet/Ru/ferromagnet stack with alternating antiferromagnetic and ferromagnetic exchange-couplings. We systematically investigate the effect of the interlayer exchange coupling J on the chiral domain wall dynamics. The domain wall moves along the wedge unidirectionally driven by an out-of-plane magnetic field in the antiferromagnetically exchange-coupled region. In the ferromagnetically exchange-coupled region, only field-induced maze domain walls can be observed. The boundary between the antiferromagnetically and ferromagnetically exchange-coupled regions can be identified according to the behavior of domain walls. The strongest antiferromagnetic exchange coupling point Jmax in our sample is determined. A simple phenomenological picture is proposed to explain our experimental results. Moreover, we demonstrate that the Néel-type domain wall near the boundary of J = 0 could be driven into motion by an applied electric current. A stripe domain wall can be observed at the boundary of J = 0 only with a negative electric current resulting from the domain wall chirality. Our results may provide a platform to investigate the domain wall chirality and pave a way to spintronic devices based on synthetic antiferromagnets.