Birth, Growth and Death of an Antivortex during the Propagation of a Transverse Domain Wall in Magnetic Nanostrips

Antivortex birth, growth and death due to the propagation of a transverse domain wall (DW) in magnetic nanostrips are observed and analyzed. Antivortex formation is an intrinsic process of a strawberry-like transverse DW originated from magnetostatic interaction. Under an external magnetic field, DW in a wider width region tends to move faster than that of a narrower part. This speed mismatch tilts and elongates DW centre line. An antivortex is periodically born near the tail of the DW centre line. The antivortex either moves along the centre line and dies on the other side of the strip, or grows to its maximum size, detaches itself from the DW, and vanishes eventually. The former route reverses the polarity of DW while the later keeps the DW polarity unchanged. The evolution of the DW structures is analyzed using winding numbers assigned to each topological defects. The phase diagram in the field-width plane is obtained and discussed.