Electron Induced Massive Dynamics of Magnetic Domain Walls
Physics and Astronomy
University of Delaware Condensed Matter Seminar
Control of magnetic textures via electric currents is an important step toward fabricating robust magnetic memory devices. We study the effect of conduction electrons on magnetic domain walls (DWs) in metallic, ferromagnetic nanowires. Using the Keldysh collective coordinate technique, we show how conduction electrons act as an external bath and derive the corresponding Langevin equations of motion for a DW including an electron-induced response kernel. The DW dynamics is described by two collective degrees of freedom: position and tilt-angle. The coupled Langevin equations therefore involve two correlated noise sources, leading to a generalized fluctuation-dissipation theorem (FDT). The DW response kernel due to electrons contains two parts: one related to dissipation via FDT, and another 'inertial' part. We prove that the latter term leads to a mass for both DW degrees of freedom, even though the intrinsic bare mass is zero. The electron-induced mass is present even in a clean system without pinning or specifically engineered potentials. The DW equations of motion contain rich dynamical solutions and point toward a new way to control domain wall motion in metals via the electronic system properties. We discuss experimental consequences including two observable signatures of the mass: hysteresis in the DW dynamics and resonant response to ac current.
Hilary Hurst. "Electron Induced Massive Dynamics of Magnetic Domain Walls" University of Delaware Condensed Matter Seminar (2019).