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PGI Colloquium: 

Prof. Dr. Hans-Benjamin Braun,
School of Physics, University College Dublin, Ireland

PGI Lecture Hall, Building 04.8, 2nd Floor, Room 365

30 Oct 2015 11:00

Topology and nanomagnetism: from the limits of magnetic data storage to magnetic monopoles and skyrmions

Whenever we consult the Web or store data in the elusive `Cloud', we tacitly rely on data stored on magnetic hard disks. We have become so used to the steady increase of storage density that it is hard to imagine that current technology is about to reach its limits. In order to keep up with Moore's law, there is a need for new ways to store data magnetically.

Topological defects such as domain walls and skyrmions have recently gained prominence as they owe their stability to their robustness against continuous deformations, similar to knots in a rope. For example, Parkin's proposed racetrack memory relies on the topological stability of domain walls, and similarly skyrmions have been proposed for such devices. In view of the continuous demand of ever increasing storage density, it is important to understand topological defects on ever decreasing length scales where thermal and quantum eects are increasingly important.

After a brief overview of magnetic topological defects I discuss their relevance for the limits of current data storage technology. It is then shown how atomically sharp domain walls acquire chirality through quantumfluctuations and how the associated spin currents have been detected via inelastic neutron scattering. In spin-ice materials, topological defects are disguised as monopoles which interact like mobile electric charges.

Finally it is demonstrated theoretically and experimentally how a magnetic vortex lattice of atomic scale may undergo a sequence of quantum phase transitions caused by Berry's phase.


H.B. Braun, Topological Eects in Nanomagnetism: from superparamagnetism to chiral quantum solitons,
Adv. Phys. 61, 1-116 (2012).
H. B. Braun. R. Hügli, L. Heyderman, Nordpole ohne Südpole, Spektrum der Wissenschaft, Feb. 2014.
Y. Zhou et al., Dynamically stabilized magnetic skyrmions, Nat. Commun. 6:8193 (2015).


Dr. Gustav Bihlmayer
Phone: +49 2461 61-4677
Fax: +49 2461 61-2850