5,356 research outputs found
Oblique Hanle Effect in Semiconductor Spin Transport Devices
Spin precession and dephasing ("Hanle effect") provides an unambiguous means
to establish the presence of spin transport in semiconductors. We compare
theoretical modeling with experimental data from drift-dominated silicon
spin-transport devices, illustrating the non-trivial consequences of employing
oblique magnetic fields (due to misalignment or intentional, fixed in-plane
field components) to measure the effects of spin precession. Model results are
also calculated for Hanle measurements under conditions of diffusion-dominated
transport, revealing an expected Hanle peak-widening effect induced by the
presence of fixed in-plane magnetic bias fields
Geometric dephasing-limited Hanle effect in long-distance lateral silicon spin transport devices
Evidence of spin precession and dephasing ("Hanle effect") induced by an
external magnetic field is the only unequivocal proof of spin-polarized
conduction electron transport in semiconductor devices. However, when spin
dephasing is very strong, Hanle effect in a uniaxial magnetic field can be
impossible to measure. Using a Silicon device with lateral injector-detector
separation over 2 millimeters, and geometrically-induced dephasing making spin
transport completely incoherent, we show experimentally and theoretically that
Hanle effect can still be measured using a two-axis magnetic field
35% magnetocurrent with spin transport through Si
Efficient injection of spin-polarized electrons into the conduction band of
silicon is limited by the formation of a silicide at the ferromagnetic metal
(FM)/silicon interface. In the present work, this "magnetically-dead" silicide
(where strong spin-scattering significantly reduces injected spin polarization)
is eliminated by moving the FM in the spin injector from the tunnel junction
base anode to the emitter cathode and away from the silicon surface. This
results in over an order-of-magnitude increase in spin injection efficiency,
from a previously-reported magnetocurrent ratio of ~2% to ~35% and an estimated
spin polarization in Si from ~1% to at least ~15%. The injector tunnel-junction
bias dependence of this spin transport signal is also measured, demonstrating
the importance of low bias voltage to preserve high injected spin polarization
Clustering documents with active learning using Wikipedia
Wikipedia has been applied as a background knowledge base to various text mining problems, but very few attempts have been made to utilize it for document clustering. In this paper we propose to exploit the semantic knowledge in Wikipedia for clustering, enabling the automatic grouping of documents with similar themes. Although clustering is intrinsically unsupervised, recent research has shown that incorporating supervision improves clustering performance, even when limited supervision is provided. The approach presented in this paper applies supervision using active learning. We first utilize Wikipedia to create a concept-based representation of a text document, with each concept associated to a Wikipedia article. We then exploit the semantic relatedness between Wikipedia concepts to find pair-wise instance-level constraints for supervised clustering, guiding clustering towards the direction indicated by the constraints. We test our approach on three standard text document datasets. Empirical results show that our basic document representation strategy yields comparable performance to previous attempts; and adding constraints improves clustering performance further by up to 20%
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