Title: Magnetic Heterostructures for Spintronic Applications
Date：October 13, 2008
By: Professor Stephan von Molnár (Department of Physics and Center for Materials Research and Technology, Florida State University, USA)
About Professor Stephan von Molnár：Professor Stephan von Molnár received his Ph.D. at University of California, Riverside in 1965. He then spent 28 years at the IBM T.J. Watson Research Center as a researcher and research manager until leaving for the Florida State University (FSU) in 1994. In addition to leading a research group focusing on spin related physics at FSU as well as more recently on biotechnology, he served as the director of the Center for Materials Research and Technology (MARTECH) for nearly 14 years. Professor von Molnár is a Distinguished Research Professor of FSU, a fellow of the American Physical Society, and a recipient of the Alexander von Humboldt Senior U.S. Scientist Award. He chaired a panel on spintronics sponsored by several agencies of the U.S. government, which conducted a worldwide study to evaluate the research efforts in spin based electronics. Professor von Molnár has authored or coauthored over 100 scientific papers with at least 5,000 citations.
Abstract：Awschalom and Kikkawa <1> have demonstrated that spin polarized carriers optically injected into III-V and II-VI semiconductors maintain their spin coherence over long times and concomitantly over surprisingly long distances, exceeding tens of micrometers, thus transporting spin information between devices is feasible.Despite many experimental advances in the intervening years the physics of spin diffusion in semiconductors has not received the detailed scrutiny it deserves. For example, the spin diffusion time in Si doped GaAs peaks near the insulator- metal transition, but the underlying mechanism remains unresolved.This talk reviews salient optical experiments and details of our efforts to create device structures for all electronic injection and potential detection of polarized spins into GaAs <2> and GaAlAs. The latter material is a persistent photoconductor for Al concentrations of ~ 30 atomic percent when doped with Si. Thus photodoping through the insulator- metal transition in one and the same sample is possible. Recent results utilizing EuS/Ga0.7Al0.3As:Si, where EuS is the ferromagnetic electrode, and plans for future work with Fe electrodes <3, 4> will be described.
<1> D. D. Awschalom and J. M. Kikkawa, Phys. Today 52, 33 (1999).
<2> J. Trbovic, C. Ren, P. Xiong, and S. von Molnár, Appl. Phys. Lett. 87, 082101 (2005).
<3> X. Lou et al., Nature Physics 3, 197 (2007).
<4> Jianhua Zhao, Institute of Semiconductors, Beijing, private communication.