Project Details
Projekt
Ultrafast Spin Caloritronic Transport
Applicant
Dr. Johannes Kimling
Subject Area
Experimental Condensed Matter Physics
Term
from 2014 to 2017
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 262433780
Spin caloritronics is an emerging research branch of contemporary solid-state physics that seeks to fill key gaps in fundamental knowledge concerning the interplay between charge, spin, and heat transport. Spin caloritronics aims at emergent technologies, e.g., for generating, manipulating, and ultimately controlling spin transport in solid-state structures and devices. The general bottleneck for studying coupled charge, heat, and spin transport is the lack of a direct meter for sensing spin currents. This means that the spin currents conjectured in spin-caloritronic effects are part of the hypotheses used for explaining the electrical signals measured. This problem is particularly critical if conceptionally new effects are claimed to be observed such as spin-heat accumulation, so-called transverse and longitudinal spin Seebeck effects, and spin Hall magnetoresistance. We assert that alternative measurements of spin-caloritronic effects are needed to independently test theory and discover new phenomena that are not apparent in standard spin-caloritronic experiments. Our proposed work is positioned at the cutting edge of spin caloritronics and ultrafast magnetization dynamics. We seek to observe, characterize, understand, and ultimately control thermally-driven spin transport in the ps-time scale and in the nm-length scale, because these are the fundamental scales where the lack of equilibrium between various thermal excitations becomes a dominating factor in the transport physics. Therefore, we propose to study typical spin-caloritronic structures and materials by ultrafast optical techniques, specifically time-domain thermoreflectance and time-resolved Kerr effect magnetometry. Furthermore, we will utilize thermally-driven ultrafast demagnetization, which provides a directional pulsed spin current source. Our major objectives are: - Cross-plane thermal transport in Co/Cu multilayers. We will provide an experimental test of an immediate consequence of spin-heat accumulation by measuring the ps-time evolution of the thermal conductance. - Thermal transport across magnetic tunnel junctions. We will provide important empirical data required for analyzing tunnel magneto Seebeck experiments by measuring the thermal resistance of typical magnetic tunnel junctions. - Thermally-driven spin tunneling. We will directly measure spin tunneling in magnetic tunnel contacts using magneto-optical detection of spin accumulation, where the spin current arises from thermally-driven ultrafast demagnetization and from Seebeck spin tunneling. - Spin coupling across normal metal/magnetic insulator interfaces. We will provide a direct and independent test of the spin coupling concept across normal metal/magnetic insulator interfaces by using our new approach for generating strong pulsed spin currents. With this experiment we test current theories explaining spin Seebeck effect, spin pumping, and spin Hall magnetoresistance.
DFG Programme
Research Fellowships
International Connection
USA
