Topological Spin-orbitronic: Towards Low Power Consumption and Energy Harvesting

Speaker: Dr. J. Carlos Rojas-Sánchez
Affiliation: Institut Jean Lamour -CNRS/Univ. Lorraine

Abstract:  Materials with large efficiency of spin-charge current interconversion are highly desirable to study new physical phenomena as well as for spintronics applications. Heavy metals or alloys exhibiting large spin-orbit coupling such as Pt, Ta or W scatter the electrons in opposite directions when they have opposite spin. Thus, an injection of charge current yields a spin current in such materials. That charge-spin current conversion phenomenon in those 3D materials is so-called Spin Hall Effect (SHE). We can exploit this effect to manipulate a magnetization in a heavy metal/ferromagnetic structure (HM/FM) as in current-induced magnetization switching experiments or current-switching of magnetization. We have just shown current-induced magnetization switching in Si-SiO₂//W(3 nm)/Co_xTb_1-x(3.5 nm)/Al(3 nm) structures. Interesting, we have found out that the temperature of the devices reach a characteristic temperature just before the switching takes place. This temperature is not the magnetic compensation temperature neither the angular compensation temperature of the CoTb ferrimagnetic alloy.

     On the other hand, new classes of materials such as 3D topological insulator which are trivial insulator in their bulk but hold metallic states in their surfaces are also highly interesting for spintronics. The spin-orbit coupling (SOC) in the 2DEG states at Topological Insulator (TI) or Rashba Interfaces is predicted to be more efficient that their 3D counterparts for spin-charge current conversion.  Indeed, we have found the highest efficiency at room temperature using the topological insulator α-Sn. The underlying physics of charge-spin current interconversion in such 2D systems is different from the SHE and is called Edelstein Effect (EE), also known as inverse spin galvanic effect. I will show results of spin-to-charge conversion by spin pumping experiments and their analysis in term of inverse Edelstein Length. Experimental results based on ARPES and spin pumping indicate that direct contact of metallic ferromagnetic layer is detrimental for the surfaces states of topological insulators but we can keep the surfaces states of α-Sn using Ag spacer. I will use the conversion parameters obtained at room temperature with α-Sn to demonstrate the very large advantage of the SOC effects in 2D interface states with respect to the Spin Hall Effect (SHE) of 3D metals and the resulting perspective for low power spintronic devices. I will focus especially in the prediction of giant spin Seebeck effect using insulator ferrimagnet Y₃Fe₅O₁₂ (YIG) in YIG/a-Sn films structures.

Biography:  Juan Carlos Rojas-Sanchez is currently a CNRS permanent researcher at Institute Jean Lamour (IJL), Nancy, France. He received his bachelor in physics in 1999 from National University of Engineering, Lima, Peru, his master in physics in 2004 from Balseiro Institute, Bariloche, Argentina, and his PhD in physics in 2011 from Balseiro Institute (National University of Cuyo), Bariloche Atomic Center, Bariloche, Argentina. From 2011-2015, he was a postdoctoral fellow in Laboratoire de Nanostructures et Magnetisme INAC/CEA, SPINTEC, Institut Néel, and Unité Mixte de Physique CNRS/Thales, France. His main research interest is spintronics devices, and he has 31 publications in international peer-reviewed journals such as Nature materials, Nature Communications, Nano Letters and Physical Review Letters, 10 as the first author and 9 as the second author, with a total citation of more than 1000. He has also served as the session chair of several significant international conferences including international conference of magnetism (ICM).

For more information, contact Prof. Kang Wang (wang@ee.ucla.edu)

Date/Time:
Date(s) - Oct 24, 2018
3:00 pm - 4:00 pm

Location:
E-IV Tesla Room #53-125
420 Westwood Plaza - 5th Flr., Los Angeles CA 90095