CM/BIO/ECE Seminar series presents: Dr. Shulei Zhang

Wednesday, December 6, 2017 4:00pm

Physics Library, Room 223A, Physics Building

Departments: 

The CM/BIO/ECE Seminar series presents, "Formation of Skyrmion Lattice Without Inversion Symmetry Breaking," by Dr. Shulei Zhang, Argonne National Laboratory, on Wednesday, Dec. 6 at 4:00 p.m. in the Physics Library, Room 223A, Physics Building. Refreshments will be served beginning at 3:30 p.m.

Dr. Shulei Zhang

Two dimensional magnetic skyrmions are nanoscale spin textures that are topologically protected: the spin structure of an individual skyrmion is associated with an integer winding number which cannot be continuously changed into another integer number without overcoming a finite energy barrier. The creation, annihilation and transport of magnetic skyrmions strongly rely on their topological properties, which make them promising candidates as spin information carriers in future spintronic devices.

The formation of skyrmions and skyrmion lattices (SkXs) in chiral magnets with inversion symmetry breaking relies on the Dzyaloshinskii-Moriya interaction

(DMI) which favors perpendicular alignment of neighboring spins. However, most chiral magnets are known to host SkX only at low temperature due to their low Curie temperatures, which hinders the application of skyrmions at room temperature. In this talk, I will demonstrate theoretically that, in ferromagnetic thin films with inverse symmetry (and hence no DMI), SkX can be stabilized by spatially varying uniaxial magnetic anisotropy with easy axis periodically rotating from in-plane to out-of-plane. The phase diagrams calculated by a Ginzburg-Landau approach indeed show that SkX state is energetically favorable at room temperature with a very small magnetic field of the order of 10 Oe. Remarkably, the size of the skyrmions is determined by the ratio of the exchange length and the period of the spatial modulation of the anisotropy, at variance with conventional skyrmions stabilized by dipolar interaction and DMI. If time permits, I will also discuss, from a theoretical point of view, the current issues in electric detection of skyrmions by using topological Hall effect – a kind of Hall effect that depends on the topology of the spin texture.