On Thursday September 26 we have the pleasure to welcome Prof. Jian-Ping WANG (University of Minnesota, MN, USA). He will give us a seminar at in CNRS Building A at 10am in the framework of Satellite Workshop of the Symposium in Homage to Dominique Givord.
Discovery of quantum confinement effect in sputtered topological insulator films and observation of room-temperature high spin-orbit torque
In this talk, I will start with my perspectives on the spintronic materials and devices. Then I will focus on the report and discussion of our recent experimental demonstration and first-principles calcuation of quantum confinement in topological insulator. First, I will report BixSe(1-x) films with high SOT at RT grown onto thermally oxidized silicon substrates by magnetron sputtering, which is a semiconductor industry compatible process. The dc planar Hall and ST-FMR methods were used for the characterization of SOT in BixSe(1-x)/CoFeB heterostructures with in-plane CoFeB. At RT, the spin Hall angle of the sputtered BixSe(1-x) film is up to two orders of magnitude larger than that of HMs. Notably, we developed perpendicular CoFeB multilayers on BixSe(1-x) films, and we demonstrated switching of the magnetization using SOT arising from the BixSe(1-x) with very low switching current density in bilayers at RT. Second, I will report our discovery of the quantum confinement effect in topological insulators. The sputter deposited BixSe(1-x) has granular structure with grain size as small as approximately 6 nm. Electronic band-structure analysis indicates that the reduced dimensionality and quantum confinement strongly influences the spintronic properties of the TI. Our theory identifies the presence of lowly dispersive surface bands with large charge-to-spin conversion efficiency in nanoscale grains, which might explain the experimentally observed enhancement in the figure-of-merit. Third, I will report the integration of the sputtered BixSe(1-x) film with CoFeB and YIG for spin to charge conversion study through spin-pumping experiment. The demonstrated ease of growth of the films on a silicon substrate and successful growth and switching of perpendicular CoFeB multilayers on BixSe(1-x) film provide an avenue for the use of BixSe(1-x) as a spin-density generator in SOT-based memory and logic devices.
1) Mahendra DC, et al, Nature Materials (2018).
2) Mahendra DC, et al, Nano Letters (2019) and Appl. Phys. Letts (2019).
3) P. Sahu, et al, to be submitted;
*This work was partially supported by C-SPIN, one of six STARnet program research centers and ASCENT, one of six JUMP program research centers.
Biography: Jian-Ping Wang is the Robert F. Hartmann Chair and a Distinguished McKnight University Professor of Electrical and Computer Engineering, and a member of the graduate faculty in Physics, Chemical Engineering and Materials Science and Biomedical Engineering at the University of Minnesota. He received his PhD degree in 1995 from Institute of Physics, Chinese Academy of Sciences, where he performed research on nanomagnetism. He established and managed the Magnetic Media and Materials program at Data Storage Institute, Singapore, as the founding manager, from 1998 to 2002. He joined the faculty of the Electrical and Computer Engineering department at the University of Minnesota in 2002 and was promoted to full professor in 2009. He was the director of the Center for Spintronic Materials, Interfaces and Novel Architectures (C-SPIN), which consists of 32 professors from 20 US universities. C-SPIN was one of six SRC/DARPA STARnet program centers and the largest vertically integrated research center on spintronic research in the world. Prof. Wang is the director of the Center for Spintronic Materials for Advanced Information Technology (SMART), one of two SRC/NSIT nCORE research centers. He received the information storage industry consortium (INSIC) technical award in 2006 for his pioneering work in exchange coupled composite magnetic media and the outstanding professor award for his contribution to undergraduate teaching in 2010. He is also the recipient of 2019 SRC Technical Excellence Award for his innovations and discoveries in nanomagnetics and novel materials that accelerated the production of magnetic random-access memories. He has authored and co-authored more than 250 publications in peer-reviewed top journals and conference proceedings and holds 42 patents. He is an IEEE fellow.