报 告 人：陈景升教授，新加坡国立大学 (National University of Singapore)
报告题目：Antiferromagnets with large spin orbit torque efficiency and Electrical
switching of single magnetic layer with perpendicular anisotropy
内容简介：Electrical manipulation of magnetization is essential for integration of magnetic functionalities such as magnetic memories and magnetic logic devices into electronic circuits. The current induced spin-orbit torque (SOT) in heavy metal/ferromagnet (HM/FM) bilayers via the spin Hall effect in the HM and/or the Rashba effect at the interfaces provides an efficient way to switch the magnetization. In current presentation, we will present our recent works on antiferromagnets with large spin orbit torque efficiency and electric switching of single magnetic layer with perpendicular anisotropy. (1) combining the results from neutron diffraction and spin-torque ferromagnetic resonance experiments, we show that the room-temperature magnetic structure of epitaxially grown L10-IrMn (a collinear AFM) is distinct from the widely presumed bulk one. It consists of two types of domains with the spin axes orienting towards  and [-111], respectively. We find that this unconventional magnetic structure is responsible for a much larger SOT efficiency up to 0.60±0.04, comparing to 0.083±0.002 for the polycrystalline face-centered-cubic IrMn. Furthermore, we reveal that the magnetic structure of L10-IrMn induces a large isotropic bulk contribution to the SOT efficiency and an anisotropic interfacial contribution of comparable magnitude, where the latter depends strongly on the electric current direction in the film plane. (2) Current induced SOT switching in a single magnetic layer has also been observed in ferromagnetic semiconductor (Ga,Mn)As and antiferromagnetic metals CuMnAs and Mn2Au with globally or locally broken inversion symmetry, respectively. Here we demonstrate the current induced magnetization switching in a single ferromagnetic layer, L10 FePt, with centrosymmetric crystal structure. The spin-orbit effective fields increase with the chemical ordering of L10 FePt films. In 20 nm FePt films with higher chemical ordering, we observe a surprisingly large charge-to-spin conversion efficiency, which is one order of magnitude larger than that in HM/FM bilayers. In addition, we find the switching current density of the 20 nm FePt film as low as 7.0×106 A/cm2.
报告人简介：Dr Jingsheng Chen is an Associate Professor in Department of Materials Science and Engineering. He obtained his Ph.D degree in 1999 in Lanzhou University, China and joined NUS in December 2007. During 2001-2007 he worked at the Data Storage Institute as a research scientist. He has authored/co-authored more than 240 refereed journal papers, 3 book chapters, holds over ten patents and has made more than 50 invited presentations in the international conferences. His research work has obtained more than 4000 non-self-citations with H index of 35. His research interest includes magnetic and oxide based non-volatile memories, spintronics, ferroelectric tunnel junction, strongly correlated oxide materials. He secured more than S$15 million research grants from government and around US$ 800k from Seagate Technology and more than S$ 1 million from Globalfoundries. The magnetic recording media in the newest generation of HDD (HAMR) applied a few his inventions.