Abstract
Understanding of ultrafast spin dynamics is crucial for future spintronic applications. In particular, the role of non-thermal electrons needs further investigation in order to gain a fundamental understanding of photoinduced demagnetization and remagnetization on a femtosecond time scale. We experimentally demonstrate that non-thermal electrons existing in the very early phase of the photoinduced demagnetization process play a key role in governing the overall ultrafast spin dynamics behavior. We simultaneously measured the time-resolved reflectivity (TR-R) and the magneto-optical Kerr effect (TR-MOKE) for a Co/Pt multilayer film. By using an extended three-temperature model (E3TM), the quantitative analysis, including non-thermal electron energy transfer into the subsystem (thermal electron, lattice, and spin), reveals that energy flow from non-thermal electrons plays a decisive role in determining the type I and II photoinduced spin dynamics behavior. Our finding proposes a new mechanism for understanding ultrafast remagnetization dynamics.
Highlights
Understanding of ultrafast spin dynamics is crucial for future spintronic applications
Another possible origin for the nontrivial time-resolved reflectivity (TR-R) trend is a strain effect triggered by laser pulse[31,32], whereas a timescale of the acoustic wave generated by the laser pulse is on a sub or few tens of picoseconds, which is much longer than the time window (2 ps) in the present study
We consider that the nontrivial TR-R behavior is still due to the non-thermal electron excitation above the Fermi energy without being involved with any specific gap structure or strain effect
Summary
Understanding of ultrafast spin dynamics is crucial for future spintronic applications. The role of non-thermal electrons needs further investigation in order to gain a fundamental understanding of photoinduced demagnetization and remagnetization on a femtosecond time scale. We experimentally demonstrate that non-thermal electrons existing in the very early phase of the photoinduced demagnetization process play a key role in governing the overall ultrafast spin dynamics behavior. By using an extended three-temperature model (E3TM), the quantitative analysis, including non-thermal electron energy transfer into the subsystem (thermal electron, lattice, and spin), reveals that energy flow from non-thermal electrons plays a decisive role in determining the type I and II photoinduced spin dynamics behavior. Recent reports indicate that the hot electrons can contribute to demagnetization and enhance magnetization on an ultrafast timescale[29], implying that the understanding and control of non-thermal electron dynamics could be crucial in future ultrafast spin applications. The analysis clearly shows that the MOKE signal is rather insensitive to the thermalization of non-thermal electrons, which confirms the necessity of simultaneous measurement ofthe reflectivity
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