Ultrafast & laser-induced magnetic control
Central quest in this research theme is to understand and control magnetization dynamics in its ultimate limits. Most extreme case is met when exciting magnetic matter by femtosecond laser pulses, driving a system into a strongly non-equilibrium state. Understanding this regime has been a significant challenge, but rapid progress is being witnessed. Most excitingly, it has been found that the laser excitation triggers a wide range of phenomena, ranging from spin wave excitation and magnetic phase transitions, to the very recently discovered all-optical switching and laser-induced spin-transfer torque. Our group is active in studying the fundamentals mechanisms leading to those novel phenomena, but also explores their potential use in entirely novel device concepts for ultrafast magnetic storage, memory and logic. Furthermore, bridging the regime between high-frequency electronics and femtosecond laser excitations provides exciting opportunities.
Femtosecond laser-excitation drives a ferromagnet into a state where electronic, spin and lattice degrees of freedom are no longer in mutual equilibrium. Combining time-resolved MOKE experiments on especially engineered multilayered structures, as well as theoretical modelling help us to understand the mechanism governing the various sub-picosecond spin-related processes
We pioneered the use of femtosecond laser pulses to trigger spin current at the ultrafast time scales. Apart from affecting the rate at which magnetic order is locally lost, it was also shown that a laser-induced spin transfer torque can be generated between adjacent layers. Another novel approach is to exploit non-equilibrium exchange rather than spin currents to control the magnetic state.
Precessional dynamics and Gilbert damping in nanomagnetic structures and devices proceed typically at GHz frequencies, a regime where high-frequency electronics and pulsed laser studies can complement. Explorations in this regime are of extreme relevance for novel routes in spintronics, ranging from switching nanomagnets to domain wall phenomena – all actively being explored within our group.