THz-driven Ultrafast Spin-Lattice Scattering In Metallic Ferromagnets
by
Stefano Bonetti(THz Physics group, Stockholm University)
→
Europe/Berlin
E1.172, European XFEL, XHQ (Campus Schenefeld, Main Building)
E1.172, European XFEL, XHQ
Campus Schenefeld, Main Building
Description
The interaction between magnetism and light is receiving considerable interest in recent years, after the groundbreaking experiments that showed that ultrashort (~100 fs) infrared light pulses can be used to demagnetize or even switch the magnetization of thin film ferromagnets.
This has sparked great excitement towards the possibility of realizing ultrafast magnetic data storage controlled by light. However, to date no clear and commonly accepted understanding of the fundamental physical processes governing the ultrafast magnetization has been reached.
In this talk, I'll present recent experiments where we used strong THz fields to excite ultrafast magnetization dynamics in thin film ferromagnets. We compared the response from two films with remarkably different lattice structure: a crystalline Fe film and an amorphous CoFeB film. We observe Landau- Lifshitz-torque magnetization dynamics of comparable magnitude in both systems, but only the amorphous sample shows ultrafast demagnetization caused by the spin-lattice depolarization of the THz-induced ultrafast spin current. Quantitative modelling shows that such spin-lattice scattering events occur on similar time scales than the conventional spin conserving electronic scattering (~30 fs). This is significantly faster that optical laser-induced demagnetization, and THz conductivity measurements point towards the influence of lattice disorder in amorphous CoFeB as the driving force for enhanced spin-lattice scattering. I will also present recent data taken using the multicycle THz pulses produced at the High-Field High-Repetition-Rate Terahertz facility @ ELBE (TELBE) to drive magnetization dynamics in those samples.
Finally, I will give an overview over the next challenges and opportunities that the use of THz radiation offers towards a deeper understanding of ultrafast magnetism, in particular in combination with the use of coherent x-ray radiation now available at free electron lasers.
