Element specific spin dynamics of nano- and heterostructues studied with ultimate spatial resolution

• Applicant: Dr. Katharina Ollefs
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2017 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 321560838

The aim of this proposal is to carry out a systematic investigation of the dynamic magnetic properties of individual magnetic micro- and nano-objects in a complex magnetic environment utilizing a novel experimental tool, which the applicants jointly developed with the beamline staff of the Stanford Synchrotron Radiation Laboratory (SSRL). This rather unique novel instrument combines element specific investigation of the magnetic properties based on X-ray magnetic circular dichoism (XMCD) with the lateral spatial resolution of nominally 35 nm of the scanning transmission x-ray microscope (STXM) as well as a time-resolved detection scheme down to 17 ps allowing to study time-resolved transversal x-ray detected ferromagnetic resonance (XFMR) with spatial resolution. The microwave excitation is based on lithographically fabricated micro-resonators on SiN membranes into which the magnetic micro- or nano-object in question will be placed. The use of these microresonators provides the unique opportunity to simultaneously investigate the conventional FMR signal which averages over the magnetic ensemble and the space resolved XFMR response of each individual nano constituent. We aim at pursuing the following range of experiments:1. spatial imaging and time resolved phase information of uniform and non-uniform spinwave excitations in micro- and nanostripes where the excitation modes are modified by the shape of the structures or by local stray-fields generated by adjacent ferromagnetic structures. These local fields can be used to enhance or suppress local excitations. Planned materials for the structures will be Co as hard and Permalloy (Py) as soft magnetic material.2. investigations of local dynamic magnetic properties of individual nanoparticles under the influence of magnetic coupling or local stray fields in an ensemble using individual Fe or Fe oxide nanoparticles. The magnetic excitation states can be tailored by arranging the nano particles in different geometries and/or number backed by micro magnetic simulations. 3. direct imaging of spin currents in a non-magnetic material generated by spin-pumping in hetero structures utilizing the element specificity, space- and time-resolution of the STXM-FMR. A Py microstripe on top of a low spin-orbit coupling material like ZnO or Al shall be driven into FMR and the spatial distribution and relative phase of the generated spin current will be imaged.

• DFG Programme: Research Grants
• International Connection: Austria
• Co-Investigator: Dr. Ralf Meckenstock
• Cooperation Partner: Professor Dr. Andreas Ney