901 research outputs found
Magnetism of 3d transition metal atoms on W(001): submonolayer films
We have investigated random submonolayer films of 3d transition metals on
W(001). The tight-binding linear muffin-tin orbital method combined with the
coherent potential approximation was employed to calculate the electronic
structure of the films. We have estimated local magnetic moments and the
stability of different magnetic structures, namely the ferromagnetic order, the
disordered local moments and the non-magnetic state, by comparing the total
energies of the corresponding systems. It has been found that the magnetic
moments of V and Cr decrease and eventually disappear with decreasing coverage.
On the other hand, Fe retains approximately the same magnetic moment throughout
the whole concentration range from a single impurity to the monolayer coverage.
Mn is an intermediate case between Cr and Fe since it is non-magnetic at very
low coverages and ferromagnetic otherwise.Comment: 5 pages, 3 figures in 6 files; presented at ICN&T 2006, Basel,
Switzerlan
Shot noise in magnetic tunnel junctions from first principles
We compute the shot noise in ballistic and disordered Fe/MgO/Fe tunnel
junctions by a wave function-matching method. For tunnel barriers with no more
than 5 atomic layers we find a suppression of the Fano factor as a function of
the magnetic configuration. For thicker MgO barriers the shot noise is
suppressed up to a threshold bias indicating the onset of resonant tunneling.
We find excellent agreement with recent experiments when interface disorder is
taken into accountComment: 5 pages,5 figure
Diabetes-Specific Distress and Glycemic Control in Children and Adolescents with Type 1 Diabetes: A Longitudinal Analysis of the Moderating Effect of Social Support
This thesis examines the roles diabetes-specific distress and social support play in impacting glycemic control trajectories in youth with type 1 diabetes. Due to the increase in responsibilities and stressors occurring during pre-adolescence and adolescence, it is particularly important to consider the impact of diabetes-specific distress on glycemic control trajectories during this time, in order to determine best practices for screening and treating this population. It is also important to consider how social support may serve as a buffer against negative diabetes outcomes. In order to determine how diabetes-specific distress and social support impact glycemic control trajectories in this population, scores on the Problem Areas in Diabetes Scale (PAID-5), Multidimensional Scale of Social Support (MSPSS), and hemoglobin A1c values over three time points were collected from 121 youth (55.4% male) between the ages of 8 and 18 years visiting a diabetes clinic at a large academic medical center in an urban city in the Midwestern United States. Multilevel modeling was used to test for the effects of diabetes-specific distress and social support on glycemic control trajectories. Results found that diabetes-specific distress significantly predicted glycemic control trajectories over time, when moderated by the significant other subscale of the MSPSS (β = -0.799, p = 0.007). A trend toward a significant interaction between diabetes-specific distress and the total social support score in predicting glycemic control trajectories was also found (β = -0.572, p = 0.053). Simple slopes analyses found that the trajectory for youth with higher levels of distress and lower levels of support (both total and for significant others) was significantly different from zero and increasing (i.e., becoming poorer) over time (Total support: β = 1.42, p = 0.033; Significant other support: β = 1.93, p = 0.007). Results suggest that diabetes-specific distress and social support may be important areas of screening and intervention for youth with type 1 diabetes
Spin-injection through an Fe/InAs Interface
The spin-dependence of the interface resistance between ferromagnetic Fe and
InAs is calculated from first-principles for specular and disordered (001)
interfaces. Because of the symmetry mismatch in the minority-spin channel, the
specular interface acts as an efficient spin filter with a transmitted current
polarisation between 98 an 89%.
The resistance of a specular interface in the diffusive regime is comparable
to the resistance of a few microns of bulk InAs.
Symmetry-breaking arising from interface disorder reduces the spin asymmetry
substantially and we conclude that efficient spin injection from Fe into InAs
can only be realized using high quality epitaxial interfaces.Comment: 4 pages, 4 figure
Interface resistance of disordered magnetic multilayers
We study the effect of interface disorder on the spin-dependent interface
resistances of Co/Cu, Fe/Cr and Au/Ag multilayers using a newly developed
method for calculating transmission matrices from first-principles. The
efficient implementation using tight-binding linear-muffin-tin orbitals allows
us to model interface disorder using large lateral supercells whereby specular
and diffuse scattering are treated on an equal footing. Without introducing any
free parameters, quantitative agreement with experiment is obtained. We predict
that disorder {\it reduces} the majority-spin interface resistance of
Fe/Cr(100) multilayers by a factor 3.Comment: 5 pages, 2 figures, submitted to PR
Effect of interface states on spin-dependent tunneling in Fe/MgO/Fe tunnel junctions
The electronic structure and spin-dependent tunneling in epitaxial
Fe/MgO/Fe(001) tunnel junctions are studied using first-principles
calculations. For small MgO barrier thickness the minority-spin resonant bands
at the two interfaces make a significant contribution to the tunneling
conductance for the antiparallel magnetization, whereas these bands are, in
practice, mismatched by disorder and/or small applied bias for the parallel
magnetization. This explains the experimentally observed decrease in tunneling
magnetoresistance (TMR) for thin MgO barriers. We predict that a monolayer of
Ag epitaxially deposited at the interface between Fe and MgO suppresses
tunneling through the interface band and may thus be used to enhance the TMR
for thin barriers.Comment: 4 pages, 3 eps figures (2 in color), revtex
A unified first-principles study of Gilbert damping, spin-flip diffusion and resistivity in transition metal alloys
Using a formulation of first-principles scattering theory that includes
disorder and spin-orbit coupling on an equal footing, we calculate the
resistivity , spin flip diffusion length and the Gilbert damping
parameter for NiFe substitutional alloys as a function of
. For the technologically important NiFe alloy, permalloy, we
calculate values of Ohm-cm, nm,
and compared to experimental low-temperature values
in the range Ohm-cm for , nm for , and
for indicating that the theoretical formalism captures
the most important contributions to these parameters.Comment: Published in Physical Review Letter
Spin-dependent Transparency of Ferromagnet/Superconductor Interfaces
Because the physical interpretation of the spin-polarization of a ferromagnet
determined by point-contact Andreev reflection (PCAR) is non-trivial, we have
carried out parameter-free calculations of PCAR spectra based upon a
scattering-theory formulation of Andreev reflection generalized to
spin-polarized systems and a tight-binding linear muffin tin orbital method for
calculating the corresponding scattering matrices. PCAR is found to measure the
spin-dependent interface transparency rather than the bulk polarization of the
ferromagnet which is strongly overestimated by free electron model fitting.Comment: 4 pages, 1figure. submitte
Tunneling anisotropic magnetoresistance driven by resonant surface states: First-principles calculations of Fe(001) surface
Fully-relativistic first-principles calculations of the Fe(001) surface
demonstrate that resonant surface (interface) states may produce sizeable
tunneling anisotropic magnetoresistance in magnetic tunnel junctions with a
single magnetic electrode. The effect is driven by the spin-orbit coupling. It
shifts the resonant surface band via the Rashba effect when the magnetization
direction changes. We find that spin-flip scattering at the interface is
controlled not only by the strength of the spin-orbit coupling, but depends
strongly on the intrinsic width of the resonant surface states.Comment: 5 pages, 3 figure
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