Directional growth of stripe domains in Co/Ni/Pt multilayers

There has recently been strong interest in the control of DW motion using magnetic fields and electric current-related effects. The Dzyaloshinskii-Moriya interaction (DMI) due to inversion asymmetry at interfaces between magnetic materials and materials with large spin-orbit coupling can transform DWs from Bloch to chiral Néel, leading to asymmetric DW propagation. However, stripe domain growth in systems with DMI is not yet well understood. Here we present an experimental study of perpendicular anisotropy Ta(3 nm)/Pt(5 nm)/[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. Kerr microscopy revealed that for N ≥ 3, magnetic reversal occurs via stripe domains. However, when a static in-plane magnetic field is applied, the domains grow in well-defined directions depending on the field strength. For low fields, the domains grow roughly perpendicular to the field. As the field increases, growth proceeds in the field direction. Above a critical field value, the propagation direction reverses, in a direction opposed to the field. Possible explanations as to the origin of these novel results will be provided.