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Monday, June 21st 2010

1:30 pm:

My thesis investigates the effects of spin-orbit coupling on spin

transport in Ferromagnet/Semiconductor heterostructures. Spin-orbit coupling is a relativistic phenomenon that couples the spin of an electron to its momentum by means of a momentum-dependent effective magnetic field. The effects of spin-orbit coupling in bulk InGaAs are observed by measuring the direct spin Hall effect, where an applied charge current induces a perpendicular spin current. The spins are oriented perpendicular to the flow directions of both the charge current and the spin current.

This spin current leads to an out-of-plane spin accumulation that is

opposite in sign at opposite edges of the channel. The spin accumulation

is identified through the observation of a Hanle effect in the Hall

voltage measured by pairs of ferromagnetic contacts. The data are fit

using a model which includes spin diffusion, precession, and relaxation.

We use the parameters determined from the fit to calculate the spin Hall

conductivity. We find that the magnitude of the spin Hall conductivity is

in agreement with models of the extrinsic SHE due to ionized impurity

scattering. By analyzing the dependence of the spin Hall signal on channel

conductivity we determine the contributions of both skew and side jump

scattering to the total spin Hall conductivity. We calculate that the

spin-orbit coupling parameter is larger than predicted by standard k•p

perturbation theory.

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