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|Title:||ALS Special Seminar|
|When:||08/28/2014 1:00 PM - 2:00 PM|
|Description:||ALS/CXRO Special Seminar|
University of Mainz
Sin Dynamics of Skyrmionic Magnetic Bubbles and Domain Walls
In nano patterned magnetic thin-film elements topological defect spin structures such as skyrmions and domain walls emerge. These structures possess a high stability and their dynamics resembles that of a composite quasi-particle. The dynamics of these structures is of key importance for magnetic memories and logic devices but also contains exciting physics and received enormous scientific interest in recent years.
In a magnetic vortex state the magnetization curls in-plane around a center region, in which the magnetization points out-of-plane. Whereas its dynamics has been widely investigated [1,2], much less is known about the dynamics of the magnetic bubble, a counterpart of the vortex in a magnetic material with easy-axis perpendicular anisotropy. The magnetization in the bubble points out-of-plane. In the remaining part, the magnetization points in the opposite direction. These two domains are separated by a Bloch-type domain wall. Magnetic bubbles are skyrmions characterized by the spherical topology of their spin vector field that can be useful for memories .
Here, we study the GHz gyrotropic motion of a skyrmion spin structure, which has recently been found from micro-magnetic simulations . Our analytical model  describes this motion in terms of two waves that travel along the domain wall that confines the bubble and the position of the bubble is then determined by the superposition of the two waves. This results in a finite momentum of the bubble quasi particle which does not exist for a magnetic vortex. Experimentally we observed this motion using pump-probe X-ray holography and we track the bubble position with 3 nm accuracy and report the first experimental observation of the GHz gyrotropic motion of a skyrmion. The trajectory of the skyrmion’s position is accurately described by our quasi particle equation of motion . From a fit we are able to deduce the inertial mass of the magnetic bubble and find it to be much larger than inertia found in any other magnetic system. We attribute the large mass to the non-trivial topology, making the results also relevant for other skyrmionic spin structures sharing the same topology .
Finally we also propose a new approach to shifting topological objects, such as in-plane domain walls using perpendicular field pulses . We demonstrate that by engineering the pulses, synchronous displacement of multiple domain walls is efficiently possible .