Northwestern Events Calendar

Oct
7
2014

MSE Colloquium: Geoffrey Beach

recurring see all events in this series

When: Tuesday, October 7, 2014
4:00 PM - 5:00 PM CT

Where: Technological Institute, L361, 2145 Sheridan Road, Evanston, IL 60208 map it

Audience: Faculty/Staff - Student - Public - Post Docs/Docs - Graduate Students

Contact: Department Office   (847) 491-3537

Group: Department of Materials Science and Engineering (MatSci)

Category: Lectures & Meetings

Description:

The Department of Materials Science and Engineering welcomes you to its 2014 Fall Colloquium Series.

Location: Tech L361, 4:00pm

Geoffrey Beach
Professor
Massachusetts Institute of Technology

Spin-Orbitronics: Interfacial Design of Spintronic Materials and Devices

There is great interest in electrically manipulating the magnetization in nanoscale materials for high-performance memory and logic device applications. In this talk I will describe recently-discovered mechanisms, based on symmetry breaking and spin-orbit coupling at interfaces, whereby the magnetization can be controlled using very low currents1,2 or by a gate voltage alone.3-5 I will focus on ultrathin transition metal ferromagnets sandwiched between an oxide and a nonmagnetic heavy metal, in which magnetic, electronic and ionic effects at the interface can be exploited in new and unexpected ways.
I first focus on the heavy-metal/ferromagnetic interface, where spin-orbit coupling influences not only spin transport, but the nature of magnetism itself in the ferromagnet. In nonmagnetic heavy metals, spin-orbit coupling leads to a left-right scattering asymmetry such that spin “up” and spin “down” electrons pile up on either side of a material when a charge current flows through it. I will show how this spin Hall effect can be used to create pure spin currents at the interface that can drive magnetization switching and domain wall motion in an adjacent ferromagnetic film.1,2 In these same materials, broken inversion symmetry can lift the chiral degeneracy and generate new topological spin textures such as spin-spirals and skyrmions. We show for the first time that chiral ferromagnetism can persist at room temperature and can be engineered simply by appropriately designing interfaces between magnetic and nonmagnetic materials.2
I will then turn to the ferromagnet/oxide interface3-6 and describe our discovery of a new class of “magneto-ionic” materials,5,6 in which a gate voltage can be used to electrochemically switch the interfacial oxidation state to realize unprecedented control over magnetic properties. Here we use Pt/Co/Gd2O3- ultrathin film stacks, where Gd2O3- serves as an efficient oxygen ion conductor. I show that the magnetization in the thin Co layer can be switched between perpendicular and in-plane orientations, or quenched entirely, by driving O2- towards or away from the Co/GdOx interface with a small gate voltage.6 I then show that magneto-ionic gates can be used to locally tune magnetic properties and create a magnetic analog of field-effect transistors.5
Finally, I will describe emerging nanomagnetic devices that utilize these and other effects for memory,3,4 logic,5 and biosensing,7 and assess the progress and outlook for a variety of applications.

Biography: Geoffrey Beach is an Associate Professor of Materials Science and Engineering at MIT. He received a B.S. in Physics from Caltech, a Ph.D. in Physics from the University of California, San Diego, and conducted postdoctoral work at the University of Texas at Austin. At MIT, Prof. Beach has established the Laboratory for Nanomagnetism and Spin Dynamics, which designs advanced materials for spin-based memory, logic, and biomedical applications. His work has been recognized with numerous awards including most recently a Deshpande Center Award for Technological Innovation, the MIT Junior Bose Award for Excellence in Teaching, the MIT Class of 1958 Institute Chaired Professorship, and the Department of Energy (DoE) Early Career Award.

1. S. Emori, D. Bono, and G. S. D. Beach, Appl. Phys. Lett. 101, 042405 (2012).
2. S. Emori, U. Bauer, S.-M. Ahn, E. Martinez, and G. S. D. Beach, Nature Materials 12, 611 (2013).
3. U. Bauer, M. Przybylski, J. Kirschner, and G. S. D. Beach, Nano Lett. 12, 1437 (2012).
4. U. Bauer, S. Emori, and G. S. D. Beach, Appl. Phys. Lett. 100, 192408; ibid 101, 172403 (2012).
5. U. Bauer, S. Emori, and G. S. D. Beach, Nature Nanotechnology 8, 411 (2013).
6. U. Bauer, L. Yao, S. Emori, H. L. Tuller, S. van Dijken, and G. S. D. Beach, under review; arXiv:1409.1843 (2014).
7. E. Rapoport, D. Montana, and G.S.D. Beach, Lab Chip. 12, 4433-4440 (2012).

 

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