Description:

The electric field experienced by a travelling electron translates, in its rest frame, to a magnetic field proportional to its velocity – a relativistic effect which is notable in crystalline lattices with heavy atoms. The Zeeman interaction between the electron spin and this effective magnetic field is equivalent to the coupling of the electronic spin and momentum degrees of freedom, known as spin-orbit coupling (SOC). Importantly, SOC effects are greatly enhanced in reduced dimensions: inversion symmetry is broken at the surface or interface, and the resultant electric field couples to the spin of itinerant electrons.

The states induced by engineering SOC and inversion symmetry breaking in magnetic materials open a broad perspective, with impact in the technology of spin topology. For example, in conventional ferromagnets the exchange interaction aligns spins and the anisotropy determines energetically preferred orientations. Meanwhile, the interaction generated by SOC and broken inversion symmetry induces a relative tilt between neighbouring spins. Magnetic skyrmions – finite-size two-dimensional (2D) ’whirls’ of electron spin – form due to the competition between these ‘winding’ & ‘aligning’ exchange interactions.

Skyrmions have several compelling attributes as prototype memory elements, namely their (1) nontrivial spin topology, protecting them from disorder and thermal fluctuations, (2) small size and self-organization into dense lattices and (3) particle-like dynamics, manipulation and addressability. Using a novel materials architecture we developed recently, I will address quantifiable insights towards understanding skyrmion stability and dynamics, and directions for exploiting their properties in nanoscale devices at room temperature.

Professor Christos Panagopoulos, Nanyang Technological University, Singapore

Host: Venkat Chandrasekhar

Keywords: Physics, Astronomy, Condensed Matter