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Graduation Commencement

Colloquium Abstract

Date: March 19 (205 Gore Hall, 4:00pm)

Speaker: Paul Crowell, School of Physics & Astronomy, University of Minnesota

Title: Spin Transport in Ferromagnet Semiconductor Heterostructures

Abstract:

A longstanding goal of research in semiconductor spintronics is the ability to inject, modulate, and detect electron spin in a single device. Over the last year, there has been explosive progress on this problem in work reported by several groups. I will discuss recent experiments on transport in ferromagnet-semiconductor heterostructures, including the electrical detection of spin accumulation and the observation of spin precession in transport. The focus of our work is on epitaxial Fe/GaAs (100) heterostructures comprising a heavily doped Schottky barrier on an n-doped channel (n = 2 ´ 10 16 – 1 ´ 10 17 cm -3). A non-equilibrium spin polarization is injected into the channel by tunneling through the Fe/GaAs Schottky barrier. Electrical spin detection is accomplished by measuring the electrochemical potential at a non-local detection contact. In this manner, a pin-valve signal which decays with increasing separation of the source and detector is observed. More importantly, the spin detection signal can be modulated by precession of the spin in the channel of the device. The devices allow us to probe quantitatively the spin lifetime and diffusion constant as well as hyperfine fields that influence spin precession and dephasing. This work was supported by ONR, the NSF MRSEC, NNIN, and IGERT programs, and the Los Alamos LDRD program.