The role of phonons in ultrafast magnetism

• Applicant: Professor Dr. Matias Bargheer
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 403035644

Ultrafast magnetism is a fascinating and highly complex field of fundamental research, which accompanies the development of the next generation of magnetic data storage and data manipulation. The complex coupling phenomena among electron-, lattice and spin-degrees of freedom under non-equilibrium conditions are studied with increasingly specific tools provided by ultrafast physics. While most research in the field is focused on the spin- and electron degrees of freedom, this project is intended to quantitatively describe the role of the lattice in ultrafast demagnetization, re-magnetization and magnetic switching. The calibration of the transient phonon temperature in the individual layers of a ferromagnetic hetero structure is essential, because the crystal lattice takes up the major fraction of thermal energy and therefore acts as a heat-bath for cooling down spins below the Curie-Temperature. For applications of the spectacular single-pulse optical switching of GdFeCo cooling below the compensation temperature counts. For the ultrafast spin-dependent Seebeck effect, the temperature gradient across an interface is the driving quantity. We would like to devote a substantial amount of the measurement time at our unique laser-based femtosecond x-ray source to ultrafast structural investigations on ferromagnetic thin film structures. The goal is to use the material-specificity of the technique to follow the heat-transport and transient strain conditions in hetero-structures on the one hand and to quantify the amplitude and spatial profile of strain waves driving magnetic precession. Quantitative and direct access to the transient crystal lattice will provide important cross-checks for competing theoretical models and at the same time in yields an alternative perspective from which ultrafast magnetism can be further developed.On the technological level, we want to establish a time-resolve magneto-optical experimental setup which operates under the same experimental conditions as the ultrafast x-ray diffraction. In particular, the parameters of the optical pulse excitation must be identical.

• DFG Programme: Research Grants