Abstract
The quasi-static strain (QSS) is the product induced by the lattice thermal expansion after ultrafast photo-excitation. Although the ultrafast spin dynamics driven by the QSS and thermal effects are barely distinguishable in time, they should be treated separately because of their different fundamental actions. By employing ultrafast Sagnac interferometry and the magneto-optical Kerr effect, we demonstrate quantitatively the existence of QSS and the decoupling of two effects counteracting each other in typical polycrystalline Co and Ni films. The Landau-Lifshitz-Gilbert and Kittel equations considering a magnetoelastic energy term showed that QSS, rather than the thermal energy, in ferromagnets plays a governing role in ultrafast spin dynamics. This demonstration provides a way to analyze ultrafast photo-induced phenomena.
Highlights
The quasi-static strain (QSS) is the product induced by the lattice thermal expansion after ultrafast photo-excitation
Using ultrafast Sagnac interferometry (USI) and a magnetooptical Kerr effect (MOKE) instrument, we demonstrate in this work that the QSS in ferromagnetic films governs the ultrafast spin dynamics from the first ps to the ns timescale
By decoupling the thermal and the QSS effects using USI and the MOKE, we proved that the QSS has a governing role over the thermal effect on the overall behavior of ultrafast spin dynamics over a wide range of time scales
Summary
The quasi-static strain (QSS) is the product induced by the lattice thermal expansion after ultrafast photo-excitation. The magnitude of the effective magnetic field Heff(t) in such case would decrease with the increasing temperature of the sub-systems or the increasing Ip. In order to figure out the effect of ηqss(t) on the precession frequency f, we solved the following LLG equation.
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