123 research outputs found
Spin-polarized Tunneling in Hybrid Metal-Semiconductor Magnetic Tunnel Junctions
We demonstrate efficient spin-polarized tunneling between a ferromagnetic
metal and a ferromagnetic semiconductor with highly mismatched conductivities.
This is indicated by a large tunneling magnetoresistance (up to 30%) at low
temperatures in epitaxial magnetic tunnel junctions composed of a ferromagnetic
metal (MnAs) and a ferromagnetic semiconductor (GaMnAs) separated by a
nonmagnetic semiconductor (AlAs). Analysis of the current-voltage
characteristics yields detailed information about the asymmetric tunnel
barrier. The low temperature conductance-voltage characteristics show a zero
bias anomaly and a V^1/2 dependence of the conductance, indicating a
correlation gap in the density of states of GaMnAs. These experiments suggest
that MnAs/AlAs heterostructures offer well characterized tunnel junctions for
high efficiency spin injection into GaAs.Comment: 14 pages, submitted to Phys. Rev.
Coercive Field and Magnetization Deficit in Ga(1-x)Mn(x)As Epilayers
We have studied the field dependence of the magnetization in epilayers of the
diluted magnetic semiconductor Ga(1-x)Mn(x)As for 0.0135 < x < 0.083.
Measurements of the low temperature magnetization in fields up to 3 T show a
significant deficit in the total moment below that expected for full saturation
of all the Mn spins. These results suggest that the spin state of the
non-ferromagnetic Mn spins is energetically well separated from the
ferromagnetism of the bulk of the spins. We have also studied the coercive
field (Hc) as a function of temperature and Mn concentration, finding that Hc
decreases with increasing Mn concentration as predicted theoretically.Comment: 15 total pages -- 5 text, 1 table, 4 figues. Accepted for publication
in MMM 2002 conference proceedings (APL
Electronic and magnetic properties of GaMnAs: Annealing effects
The effect of short-time and long-time annealing at 250C on the conductivity,
hole density, and Curie temperature of GaMnAs single layers and GaMnAs/InGaMnAs
heterostructures is studied by in-situ conductivity measurements as well as
Raman and SQUID measurements before and after annealing. Whereas the
conductivity monotonously increases with increasing annealing time, the hole
density and the Curie temperature show a saturation after annealing for 30
minutes. The incorporation of thin InGaMnAs layers drastically enhances the
Curie temperature of the GaMnAs layers.Comment: 4 pages, 6 figures, submitted to Physica
Non-Drude Optical Conductivity of (III,Mn)V Ferromagnetic Semiconductors
We present a numerical model study of the zero-temperature infrared optical
properties of (III,Mn)V diluted magnetic semiconductors. Our calculations
demonstrate the importance of treating disorder and interaction effects
simultaneously in modelling these materials. We find that the conductivity has
no clear Drude peak, that it has a broadened inter-band peak near 220 meV, and
that oscillator weight is shifted to higher frequencies by stronger disorder.
These results are in good qualitative agreement with recent thin film
absorption measurements. We use our numerical findings to discuss the use of
f-sum rules evaluated by integrating optical absorption data for accurate
carrier-density estimates.Comment: 7 pages, 3 figure
Saturated Ferromagnetism and Magnetization Deficit in Optimally Annealed (Ga,Mn)As Epilayers
We examine the Mn concentration dependence of the electronic and magnetic
properties of optimally annealed Ga1-xMnxAs epilayers for 1.35% < x < 8.3%. The
Curie temperature (Tc), conductivity, and exchange energy increase with Mn
concentration up to x ~ 0.05, but are almost constant for larger x, with Tc ~
110 K. The ferromagnetic moment per Mn ion decreases monotonically with
increasing x, implying that an increasing fraction of the Mn spins do not
participate in the ferromagnetism. By contrast, the derived domain wall
thickness, an important parameter for device design, remains surprisingly
constant.Comment: 8 pages, 4 figures, submitted for Rapid Communication in Phys Rev
Double jeopardy: the influence of excessive daytime sleepiness and impaired cognition on health‐related quality of life in adults with heart failure
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106066/1/ejhfhfs054.pd
Predictors of Objectively Measured Medication Nonadherence in Adults With Heart Failure
Background—Medication nonadherence rates are high. The factors predicting nonadherence in heart failure remain unclear. Methods and Results—A sample of 202 adults with heart failure was enrolled from the northeastern United States and followed for 6 months. Specific aims were to describe the types of objectively measured medication adherence (eg, taking, timing, dosing, drug holidays) and to identify contributors to nonadherence 6 months after enrollment. Latent growth mixture modeling was used to identify distinct trajectories of adherence. Indicators of the 5 World Health Organization dimensions of adherence (socioeconomic, condition, therapy, patient, and healthcare system) were tested to identify contributors to nonadherence. Two distinct trajectories were identified and labeled persistent adherence (77.8%) and steep decline (22.3%). Three contributors to the steep decline in adherence were identified. Participants with lapses in attention (adjusted OR, 2.65; P=0.023), those with excessive daytime sleepiness (OR, 2.51; P=0.037), and those with ≥2 medication dosings per day (OR, 2.59; P=0.016) were more likely to have a steep decline in adherence over time than to have persistent adherence. Conclusions—Two distinct patterns of adherence were identified. Three potentially modifiable contributors to nonadherence have been identified
Photoemission studies of GaMnAs: Mn-concentration dependent properties
Using angle-resolved photoemission, we have investigated the development of
the electronic structure and the Fermi level pinnning in GaMnAs
with Mn concentrations in the range 1--6%. We find that the Mn-induced changes
in the valence-band spectra depend strongly on the Mn concentration, suggesting
that the interaction between the Mn ions is more complex than assumed in
earlier studies. The relative position of the Fermi level is also found to be
concentration-dependent. In particular we find that for concentrations around
3.5--5% it is located very close to the valence-band maximum, which is in the
range where metallic conductivity has been reported in earlier studies. For
concentration outside this range, larger as well as smaller, the Fermi level is
found to be pinned at about 0.15 eV higher energy.Comment: REVTeX style; 7 pages, 3 figure
Building capacity without disrupting health services: public health education for Africa through distance learning
The human resources crisis in Africa is especially acute in the public health field. Through distance education, the School of Public Health of the University of the Western Cape, South Africa, has provided access to master's level public health education for health professionals from more than 20 African countries while they remain in post. Since 2000, interest has increased overwhelmingly to a point where four times more applications are received than can be accommodated. This home-grown programme remains sensitive to the needs of the target learners while engaging them in high-quality learning applied in their own work contexts
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