Plasmon-assisted manipulation of spin dynamics with light – reaching the terahertz regime

• Applicant: Dr. Aleksandra Lindner
• Subject Area: Experimental Condensed Matter Physics ; Solid State and Surface Chemistry, Material Synthesis
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 530111853

The vividly developing field of plasmonics aims - among others - to explore surface plasmon resonance related phenomena in plasmonic nanocrystals (NCs) and their potential applications. State-of-the-art chemical methods allow design and fabrication of the NCs and their 2D assemblies with tailored spectral properties, which can conveniently be used to introduce an optical handle to the system of interest. Merging the plasmonic and magnetic nanoworlds offers a rich variety of multi-responsive and multi-functional nanosystems, where, via absorption of light by plasmons, magnetic properties of matter can be modified. The mainstream of this research focuses, however, on light induced changes of static magnetic properties. Controlling/triggering spin currents (or spin dynamics) with external stimulus such as continuous low-power white light (and not ultrashort high-power laser pulses), even though very promising, so far attracted very limited attention. In other words, whereas corresponding light-driven or light-mediated processes in the field of electronics are well studied and broadly utilized (e.g. solar cells or light emitting diodes), very little is known about the possible role of such light in the field of spintronics and spin dynamics. Hence, the general goal of this project is to explore the role of plasmon-mediated processes in the excitation and influencing of magnetization dynamics (plasmon-mediated spindynamics), with final (long-term) goal being to influence/drive nanometer spin waves (magnons) with visible light. For that purpose, NCs of desired optical properties will be fabricated and arranged on the surface of thin ferromagnetic films in such a way that light sensitivity of as prepared hybrid structures will serve as an optical handle to induce/affect the precessional motion of spins in a ferromagnetic layer (spin dynamics). Ferromagnetic resonance will probe the magnetization dynamics in the frequency domain, where the sample illumination, resulting in the surface plasmon resonance excitation of NCs, is expected to either damp or anti-damp the precessional motion of spins and/or shift the ferromagnetic resonance frequency, thereby allowing the use of light for controlling dynamic magnetic properties of such system. At the same time, magnetization dynamics in these hybrids will be studied in time domain using time-resolved magneto-optics. Terahertz magnons generated by pulses of terahertz radiation are expected to be affected (precessional amplitude, frequency, decay time) by surface plasmons simultaneously excited due to absorption of light. Additionally, the generation of terahertz magnons is explicitly expected via plasmon excitation using femtosecond laser pulses. This way, a detailed mechanistic picture of magnon excitations at GHz to THz frequencies within the hybrid structures under illumination will be obtained.

• DFG Programme: Research Grants
• International Connection: France
• Co-Investigator: Dr. Kilian Lenz
• Cooperation Partner: Professor Dr. Olivier Margeat