Dynamics and switching processes for magnetic bubbles in nanoelements

Abstract

We study numerically the dynamics of a magnetic bubble in a disk-shaped magnetic element which is probed by a pulse of a magnetic field gradient. Magnetic bubbles are nontrivial magnetic configurations which are characterized by a topological (skyrmion) number $\mathcal{N}$ and they have been observed in mesoscopic magnetic elements with strong perpendicular anisotropy. For weak fields we find a skew deflection of the axially symmetric $\mathcal{N}=1$ bubble and a subsequent periodic motion around the center of the dot. This gyrotropic motion of the magnetic bubble is shown here for the first time. Stronger fields induce switching of the $\mathcal{N}=1$ bubble to a bubble which contains a pair of Bloch lines and has $\mathcal{N}=0$. The $\mathcal{N}=0$ bubble can be switched back to a $\mathcal{N}=1$ bubble by applying again an external field gradient. Detailed features of the unusual bubble dynamics are described by employing the skyrmion number and the moments of the associated topological density.