Chirality-driven growth of stripe domains in Co/Ni/Pt-based multilayers*

The interfacial Dzyaloshinskii-Moriya interaction (iDMI) arising from inversion asymmetry at interfaces between magnetic materials and heavy metals with large spin-orbit coupling can transform DWs from Bloch to chiral Néel, leading to asymmetric DW propagation in the presence of a symmetry-breaking in-plane magnetic field. However, stripe domain growth in systems with iDMI is not yet well understood. Here we present an experimental study of [Co(0.7 nm)/Ni(0.5 nm)/Pt(0.7 nm)]_N (1 ≤ N ≤ 5) multilayers designed to have asymmetric Pt/Co and Ni/Pt interfaces and perpendicular anisotropy. Kerr microscopy reveals that for N ≥ 3, reversal occurs via stripe domains and that when a static in-plane magnetic field is applied, the growth directionality is strongly linked to the field strength. For low fields, the domains grow roughly perpendicular to the field – a directionality not predicted by current understanding of the iDMI. The propagation direction becomes strongly collinear to the field at higher field magnitudes, as expected from the iDMI. Possible explanations in terms of a mixed domain wall with a mixed chiral Neel and chiral Bloch character will be discussed.