An experimental approach to trigger ultrafast spin dynamics at frequencies of the terahertz (THz) regime is explored by directly incorporating ferromagnetic Ni80Fe20 films to a Fe/Au spintronic-THz-emitter. It is found that Ni80Fe20 magnetization is directly coupled to the terahertz magnetic fields, in which the magnetic responses of Ni80Fe20 are phase-locked with terahertz pulses. High efficiency of metallic spintronic-terahertz emitters in driving terahertz-induced magnetization dynamics is observed; the maximum precession amplitude of the out-of-plane component of the Ni80Fe20 magnetization reaches over 10% of its saturation magnetization. Analytical integrations of THz magnetic field pulses reproduce the experimental results, confirming that the underlying mechanism of the observed spin dynamics is the Zeeman coupling between the terahertz magnetic field and magnetization in the Ni80Fe20 film. Our results open up possibilities for the studies of terahertz spin dynamics by integrating highly efficient low-cost metallic spintronic-THz-emitters into magnetic thin film elements.
The achievement of the larger Magneto-optical Kerr rotations in nanoscale layered structures is extremely important for both theoretical understandings and practical applications. In this paper, we propose a scheme for simultaneously detecting the Kerr rotation and the Kerr ellipticity based on the weak-value amplification (WVA) technique. In the Magneto-optical Kerr effect study for the layered structure, the Kerr rotation and the Kerr ellipticity are obtained by calculating the boundary matrix and the transmission matrix of the layered structure. Then, the Kerr rotation and the Kerr ellipticity can be effectively amplified as the parameters of the pre-selection in the standard weak measurement. In addition, we numerically investigate the dependence of the thickness d of Co in the nanoscale layered structure HfO2 (10~nm)/Co(d nm)/ HfO2 (30 nm)/Al(40 nm)Si films and the Co(d nm)Si films at the measurement range of 5 nm < d < 50 nm. Simulation results confirmed that the Kerr rotation and the Kerr ellipticity can be effectively amplified by choosing the appropriate post-selected state, especially when the nanoscale layered structure shows no advantage for enhancing Kerr signals over the Co(d nm)/Si films without the weak-value-amplification technique. The realization of enhancement of Kerr signals in a nanoscale layered structure may have an important application in the magneto-optic (MO) parameters measurement and the MO properties in a more complex nanoscale structure.
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