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Seminar by Dr. Ashis Nandy

Friday, January 20, 2017 - 15:30
SPS Seminar Room
Dr Ashis Nandy
Uppsala University, Sweden
Dr. Subhankar Bedanta

Skyrmions which are localized magnetic vortices with particle-like properties may occur as stable or metastable states in chiral magnets. The unique static and dynamic properties of magnetic skyrmions driven by their nontrivial topology offer attractive perspectives for future spintronic applications and interesting objects for fundamental research. Of particular interests is atomic-scale skyrmions either appear isolated or in the form of a lattice, whose stability is expected to be robust over a large range of magnetic fields and temperatures. This brings into play ultrathin layers of chiral magnets with nonmicromagnetically describable magnetic behavior due to the competing ferro- and antiferromagnetically coupled exchange interactions between different atomic sites that are finally the origin of stable exchange spin spirals of atomic length scale. In this case, the spin-orbit coupling in the presence of broken inversion symmetry ensures strong Dzyaloshinskii-Moriya interaction which select a particular chirality of the spirals. Based on density functional theory and atomistic spin dynamics simulations, we have extended the micromagnetic concept of stabilizing skyrmions by applied magnetic fields to skyrmions stabilized by interlayer exchange coupling. This enables engineering zero field skyrmion phases in chiral magnets and provides a perspective direction to extend the number of possible systems where magnetic skyrmions can be observed also at elevated temperatures. It is again necessary to understand the dynamic properties of skyrmions within the general framework of fundamental physics before it can be exploited in devices. We further present how the topological charge of an isolated skyrmion can be used as an information bit in a data storage devices. The individual skyrmion can be nucleated in a finite domain by a single magnetic pulse and then another pulse is used for controlled switching between two isolated states with opposite polarity and topological charge. This occurs through a complex energy landscape with various local minima of transient topological states: a chiral-achiral meron pair, an achiral skyrmion and a half-switched skyrmion.

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