Evangelos Papaioannou
Recent developments in nanomagnetism and spintronics have enabled the use of ultrafast spin physics for terahertz (THz) emission [1,2]. In this presentation, we explore the potential of spintronic THz emitters (STE) for stronger THz radiation and adjustable bandwidth by addressing alloyed layers, interfaces and the role of the charge current dynamics.
We first address the need to find the best material combination of ferromagnetic (FM) and nonmagnetic (NM) layer. We show that we can drastically modify the THz emission by inducing alloyed FM/NM phases. We use Fe/Pt bilayers as a model system to induce different alloyed phases in the layers. We show that the L10-FePt phase as an interlayer can boost the THz emission [3]. Other phases like the Fe3Pt and FePt3 can also modify the strength of the spin current and the interface transmission.
Next, we reveal that not only the spin current dynamics but also the charge redistribution is important for the properties of the THz signal. The charge relaxation leads to a current backflow with a delay and a time constant that mainly depends on the conductivity and the dielectric properties of the emitter [4]. We discuss how the ultrafast charge redistribution accounts for significantly changes of profile in time of the THz pulse and we show that the time constant of the system reduces the lower frequency part of the spectrum but not the higher frequencies.
References
[1] E. Th. Papaioannou, René Beigang, Nanophotonics 10(4), 1243-1257, (2021).
[2] T. S. Seifert et al., Appl. Phys. Lett. 120, 180401 (2022).
[3] L. Scheuer, M. Ruhwedel, D. Karfaridis, I. Vasileiadis, D. Sokoluk, G. Torosyan, G. Vourlias, G. Dimitrakopoulos, M. Rahm, B. Hillebrands, T. Kehagias, R. Beigang, E.Th. Papaioannou, iScience 25, 104319, (2022).
[4] G. Schmidt, B. Das-Mohapatra, E. Th. Papaioannou, Phys. Rev. App. 19, L041001 (2023).