Stability of the 2pi-vertical-Bloch-line in a canted antiferromagnetic system

Abstract

We investigate topological defects in canted antiferromagnetic materials with the orthoferrite as a model system, and demonstrate that a vertical Bloch line (VBL), a topological defect within magnetic domain walls, can couple to the other VBL to form a stable antibonding state. Actually, such a 2pi-VBL is a topologically non-trivial object with a skyrmion number equivalent to that of the skyrmion itself. We demonstrate that transitions to other topological objects are possible only when a strong enough magnetic field is applied; the 2pi-VBL can transform to two-independent pi-VBLs under the magnetic field applied along the orthorhombic a-axis, and it can be annihilated with the magnetic field applied along the c-axis. As long as the 2pi-VBL is in a stable condition, it can be driven by the magnetic field to move straightly with a high speed of about 2000 m/s. This unique property of the 2pi-VBL can provide us with a possibility to exploit it as another topological magnetic defect for the spintronic applications.