Skyrmion spectroscopy in ferro- and antiferromagnets

• Applicant: Professor Dr. Philipp Pirro, since 5/2019
• Subject Area: Experimental Condensed Matter Physics ; Theoretical Condensed Matter Physics
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 403512431

Combining expertise in theory and in Brillouin light scattering spectroscopy, we will explore the magnetic eigenmodes of skyrmions in ferro- and antiferromagnetic thin films including their excitations due to external stimuli. The main objective is to obtain a general picture for understanding and controlling magnetic excitations within single skyrmions and within skyrmion lattices. Our main experimental tool will be Brillouin light scattering spectroscopy (BLS). Regarding spin excitations in thin films, BLS excels over other existing techniques, since its high sensitivity allows for the detection of thermally excited magnetic eigenmodes of various symmetries, even from individual microstructures. BLS has evolved into one of the leading techniques for the quantification of the strength of the Dzyaloshinskii-Moriya interaction in thin films, and we will offer this experimental tool to all members of the SPP for a (comparative) analysis of their layers. The main aim of this project is to address several key issues of skyrmion excitations using a combined approach of state-of-the-art theoretical concepts, simulations and BLS experiments. The first goal will be the analysis and understanding of the thermally populated spectra of skyrmion lattices and individual skyrmions at room temperature. Here, BLS provides a unique way to access skyrmion excitations with finite wave vector. The second key goal is a comprehensive picture of linear skyrmion excitations in the presence of external stimuli. As stimuli, we will consider radiofrequency magnetic fields and spin currents. From the excited spectra, we will obtain valuable insights into the underlying processes which govern the skyrmion dynamics. As the third key issue, we will address the nonlinear skyrmion excitations arising from strong external drivings and their implications for skyrmion-based technologies like skyrmion racetrack memories or skyrmion nano-oscillators for radiofrequency applications. In our room temperature experiments, we will focus on layer systems incorporating ferromagnetic thin films which can be used in state-of-the-art spintronic devices where skyrmion eigenmodes typically feature GHz frequencies. To extend the field of skyrmionics to higher skyrmion velocities and to overcome the THz gap, each of the aforementioned goals also covers theoretical predictions for the corresponding phenomena in antiferromagnets, where dynamics are substantially different. This will include theories for antiferromagnetic skyrmion excitations and dynamics under controlled magnon fluxes. These theories in combination with our experimental results on ferromagnetic skyrmion dynamics will outline the path how skyrmion spectroscopy can be extended to the THz range inherent to antiferromagnetic dynamics which sets the goal for the next cycle. This will stimulate novel experiments on the creation and manipulation of antiferromagnetic skyrmions and their dynamics.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2137: Skyrmionics: Topological Spin Phenomena in Real-Space for Applications
• Co-Investigator: Professor Dr. Burkard Hillebrands
• Ehemaliger Antragsteller: Dr. Thomas Brächer, until 4/2019