Deterministically switching the Bloch chirality of domain walls and skyrmions: the Dzyaloshinskii astroid

Abstract: We present a mechanism for deterministic control of the Bloch chirality in magnetic domain walls and skyrmions, originating from the interplay between an interfacial Dzyaloshinskii$-$Moriya interaction (DMI) and a perpendicular magnetic field. Although conventional interfacial DMI favors chiral N\'eel skyrmions, it does not break the energetic symmetry of the two Bloch chiralities in mixed Bloch$-$N\'eel skyrmions. However, the energy barrier to switching between Bloch chiralities does depend on the sense of rotation, which is dictated by the direction of the driving field. Our analytical and micromagnetic analyses of steady-state Dzyaloshinskii domain wall dynamics culminates in a switching diagram akin to the Stoner$-$Wohlfarth astroid, revealing the existence of achiral, chiral, and precessional Bloch regimes; we further show that in view of established energetic models, skyrmions should exhibit the same fundamental behavior. Finally, we discuss a recent theory of vertical Bloch line$-$mediated deterministic Bloch chirality in the precessional regime and extend these arguments to lower driving fields. This work establishes that the Bloch chirality of magnetic solitons can be switched on demand with applied fields, as indicated by the Dzyaloshinskii astroid.