Description:

Title: Microscopic studies of spin current generation at interfaces

Speaker: Dr. Rohan Adur, Ohio State University

Abstract: Spintronics, which uses electron spin instead of charge to transfer information, requires the generation and transport of angular momentum in the form of a pure spin current. One form of spin current generation uses the precession of a ferromagnet in contact with a normal metal in a technique known as spin pumping. The resulting spin current can be measured directly in the metal when converted to a charge current via the inverse spin hall effect (ISHE). While the majority of work in the field of spin pumping has investigated the uniform precession of the ferromagnet, also known as the ferromagnetic resonance mode, we have recently looked at the spin pumping efficiency of non-uniform spin waves in a thin film ferromagnet in contact with metal, and find that the spin current generated in the metal is not sensitive to the wavevector of the spin wave in the ferromagnet. We can also control these spin waves in a ferromagnetic film by localizing them into “magnetic particle in a box” states using the dipolar field from a nearby probe magnet as a “field well”. By measuring the damping rate of these localized spin wave modes as a function of mode radius we find that there persists a spin pumping effect, even in the absence of an adjacent metal. This intralayer spin pumping effect in an insulating ferromagnet suggests that spin pumping as a form of angular momentum and energy transport is a general effect that does not always require a ferromagnet-normal metal interface or the presence of conduction electrons. We extend this idea to another all-insulator system: diamond in contact with a ferromagnet. Here, the spin state of nitrogen-vacancy defects in diamond spin state can be measured optically. We find that is possible to directly observe the ferromagnetic resonance response of the ferromagnet by looking at the spin state of the diamond, a demonstration of spin transport from an insulating ferromagnet to an insulating paramagnet.

Keywords: Physics, Astronomy, CMP