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National Repository of Grey Literature 2 records found  Search took 0.00 seconds. 
Study of spin dynamics in magnetic metals using terahertz and optical spectroscopy
 Jechumtál, Jiří ; Nádvorník, Lukáš (advisor) ; Dědič, Václav (referee)
Understanding of the ultrafast spin dynamics is essential for application and further development of new spintronic devices. The ultrafast spintronics is a promising path towards faster and less energetically demanding technologies comparing to current electronics. Recent studies have reported on a novel possi- bility of investigation of ultrafast out-of-plane spin transport using the technique of spintronic generation of terahertz (THz) pulses. This work focuses on deter- mining the nature of out-of-plane spin transfer in spintronic THz emitters by direct experimental quantification of the spin current relaxation length and the speed of spin propagation. Our results suggest that the ultrafast spin currents are of the ballistic nature and the spin current relaxation time is limited by the scaterring time and the relaxation length by the mean free path. Another recentely published method, also used in this work, is the the contactless THz measurement of anisotropic magnetoresistance (AMR). In a thin layer of cobalt- iron, we demonstrate that the AMR, a central phenomenon commonly used in the antiferromagnetic spintronics to read the state of magnetic order, can be investigated by the THz spectroscopy even if dominated by the crystalline term. We complement the study by a spectral analysis of the crystalline...
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Study of terahertz radiation emitted using spintronic effects
 Jechumtál, Jiří ; Nádvorník, Lukáš (advisor) ; Kašpar, Zdeněk (referee)
Effective emission of picosecond terahertz (THz) pulses using optical femtosecond pul- ses is the basis of THz spectroscopy in the time domain. Recent studies have shown that ultrafast optical excitation of thin metal magnetic multilayers leads to effective emission of THz pulses by converting the spin current to electric current. This work focuses on deter- mining the absolute emission and conversion efficiency of spintronic emitters from several manufacturers. Our comparison suggests that efficiency comparable to highly optimized spintronic emitters can be achieved by utilizing multilayer manufacturing capabilites of the Faculty of Mathematics and Physics of Charles University. The work also demon- strates the significant influence of interface quality on the throughput of ultrafast spin currents. Furthermore, the work describes a saturation effect observed in the relation be- tween emission and optical excitation fluency, which defines suitable excitation conditions for scaling the THz emission to higher electric fields. The observed spectral dependence of emission on fluence complements the discussion about the nature of ultrafast spin current formation. 1
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