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Topological Effects in Nanomagnetism: From Perpendicular Recording to Monopoles

Event Details

Event Dates: 

Thursday, October 9, 2014 - 5:30pm

Seminar Location: 

  • Other

Seminar Location Other: 

Center for Community (C4C) Room S435

Speaker Name(s): 

Hans-Benjamin Braun

Speaker Affiliation(s): 

University College Dublin, Ireland
Seminar Type/Subject

Event Details & Abstract: 

Similar to knots in a rope, the magnetization in a material can form particularly robust configurations. Such topologically stable structures include domain walls, vortices and skyrmions, which are not just attractive candidates for future data storage applications but are also of fundamental importance to current memory technology. For example, the creation of domain wall pairs of opposite chirality delimits the thermal stability of bits in present high anisotropy perpendicular recording media. This talk will be adapted to the interests of the audience and will start with an overview over topological defects in magnetic systems. It is demonstrated how the geometric Berry’s phase allows micromagnetics to be extended to include quantum effects. As an important consequence it will be shown how the chirality of a classical domain wall translates into quantum spin currents, which in turn can be used for information transport. All concepts will be illustrated by state-of-the-art experiments. The final part of the talk will discuss how magnetic monopoles emerge as topological defects in densely packed arrays of nanoislands, which effectively interact as dipoles, a system also known as ‘artificial spin ice’. In  contrast to conventional thin films, where magnetization reversal occurs via nucleation and extensive domain growth, magnetization reversal in 2D artificial spin ice is restricted to an avalanche-type formation of 1D strings. These objects constitute classical versions of Dirac strings that feed magnetic flux into the emergent magnetic monopoles.

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