Physikalische Chemie - Direktor: Prof. Dr. Martin Wolf
Department Seminar
Host: Laurenz Rettig

Wednesday, February 22, 2023, 2:00 pm
All are invited to meet around 1:40 pm for a chat with coffee & cookies.
PC Seminar Room, G 2.06, Faradayweg 4
Amine Wahada
Max-Planck-Institut für Mikrostrukturphysik, Halle
Ultrafast spin transport through oxide barriers measured by inverse spin Hall effect
A femtosecond laser pulse triggers an ultrafast spin current pulse in a transition metal ferromagnet/heavy metal bilayer. The heavy metal acts as a spin detector with the ability, owing to the inverse Spin Hall effect, to convert the spin current into a transient charge current. This charge current radiates a THz pulse, making this simple bilayer an efficient spintronic THz emitter. In this talk, I will show how we are able to measure such currents electrically on-chip. We then probe the spin current transport in thin film fabricated heterostructures where a specific oxide layer is inserted between the ferromagnet and the heavy metal.
First, we consider the spin current transport in a magnesium oxide (MgO) layer and demonstrate a short spin diffusion length of 2Å. Surprisingly, we show that heavy metal 5d elements with less than half-filled d shells significantly hinder the spin current transmission due to magnetic moment reduction of the ferromagnetic layer at the interface. Based on theoretical calculations, we prove that this effect is due to 3d-5d orbital hybridization effects and can be eliminated with the insertion of a thin MgO or tantalum nitride (TaN) layer. Furthermore, we fabricated a multilayer where MgO is used to decouple multiple spintronic THz emitters. For a specific number of repeats, we show that its on-chip performance is almost doubled and significantly exceeds its free-space radiation output.
In the second part, we excite a transient magnonic current in La0.67Sr0.33MnO3/LaFeO3 (LFO)/Pt trilayers, which we monitor electrically for different LFO thicknesses. In contrast to the short spin dissipation length in MgO, we demonstrate a long distance transport of the spin angular momentum in LFO, which we attribute to its antiferromagnetic order, and extract a magnon diffusion length of ~4nm.