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Departmental Colloquium


Spin Injection from Ferromagnets into Semiconductors: Interface Effects and Spin Relaxation

Christoph Adelmann
Chemical Engineering and Materials Science, University of Minnesota

Time
 
Tue. August 2, 2005     11:30 AM     Stirling C

Abstract
 

Spintronics is an emerging new field of electronics that proposes to use spin instead of charge for information processing. A crucial part of spintronic devices is the electrical injection of spin polarized electrons from ferromagnetic contacts into semiconductor structures. Recently, it has been shown that efficient spin injection is possible from Fe into GaAs by tunneling through a reverse-biased Schottky contact.

In this presentation, the influence of the chemical, electronic, and magnetic interface structure on spin transport across the interface will be discussed with particular focus on the Fe/GaAs system. The magnetic properties of the Fe/GaAs interface have previously been studied and discussed in terms of the formation of a "magnetically-dead layer" at the interface due to Fe/GaAs reactions. I will show that the effect of interface formation on spin transport is more complex than this simple model and a remarkable wealth of spin injecting interfaces with different properties is found.

Optimized Fe/(Al,Ga)As heterostructures show an injected steady-state electron spin polarization of ~40% at 2K. Assuming the spin polarization of bulk Fe of 42%, this would correspond to near unity spin injection efficiency. The temperature and bias dependence of spin injection is discussed in terms of spin relaxation in GaAs quantum wells and bulk GaAs. Room temperature spin injection of at least 8% is demonstrated.

Also, first results of the imaging of spin transport in lateral heterostructures will be shown and spin drift after electrical spin injection over tens of microns in a semiconductor device will be demonstrated. It is also shown that electrical detection of optically injected spin is possible using Fe/GaAs Schottky contacts. This path will ultimately lead to all-electric semiconductor spintronic devices.

Refreshments will be available after the talk. Christoph Adelmann is a short-listed candidate for the recently-advertised position in Experimental Condensed Matter Physics.

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