457 research outputs found
Indirect exchange in GaMnAs bilayers via spin-polarized inhomogeneous hole gas: Monte Carlo simulation
The magnetic order resulting from an indirect exchange between magnetic
moments provided by spin-polarized hole gas in the metallic phase of a GaMnAs
double layer structure is studied via Monte Carlo simulation. The coupling
mechanism involves a perturbative calculation in second order of the
interaction between the magnetic moments and carriers (holes). We take into
account a possible polarization of the hole gas due to the existence of an
average magnetization in the magnetic layers, establishing, in this way, a
self-consistency between the magnetic order and the electronic structure. That
interaction leads to an internal ferromagnetic order inside each layer, and a
parallel arrangement between their magnetizations, even in the case of thin
layers. This fact is analyzed in terms of the inter- and intra-layer
interactions.Comment: 17 pages and 14 figure
Nonequilibrium spin distribution in single-electron transistor
Single-electron transistor with ferromagnetic outer electrodes and
nonmagnetic island is studied theoretically. Nonequilibrium electron spin
distribution in the island is caused by tunneling current. The dependencies of
the magnetoresistance ratio on the bias and gate voltages show the
dips which are directly related to the induced separation of Fermi levels for
electrons with different spins. Inside a dip can become negative.Comment: 11 pages, 2 eps figure
Spin flip scattering in magnetic junctions
Processes which flip the spin of an electron tunneling in a junction made up
of magnetic electrodes are studied. It is found that: i) Magnetic impurities
give a contribution which increases the resistance and lowers the
magnetoresistance, which saturates at low temperatures. The conductance
increases at high fields. ii) Magnon assisted tunneling reduces the
magnetoresistance as , and leads to a non ohmic contribution to the
resistance which goes as , iii) Surface antiferromagnetic magnons,
which may appear if the interface has different magnetic properties from the
bulk, gives rise to and contributions to the magnetoresistance and
resistance, respectively, and, iv) Coulomb blockade effects may enhance the
magnetoresistance, when transport is dominated by cotunneling processes.Comment: 5 page
Granular systems in the Coulomb blockade regime
Disordered granular systems, at temperatures where charging effects are
important, are studied, by means of an effective medium approximation. The
intragrain charging energy leads to insulating behavior at low temperatures,
with a well defined Coulomb gap. Non equilibrium effects can give rise to a
zero temperature transition between a metallic, gapless phase, and an
insulating phase
Causal attribution of mental illness in south-eastern Nigeria
Background:
Understanding of mental illness in sub-Saharan Africa has remained under-researched in spite of the high and increasing neuropsychiatric burden of disease in the region.
Aims:
This study investigated the causal beliefs that the Igbo people of south-eastern Nigeria hold about schizophrenia, with a view to establishing the extent to which the population makes psychosocial, biological and supernatural attributions.
Method:
Multi-stage sampling was used to select participants (N = 200) to which questionnaires were administered.
Results:
Mean comparison of the three causal models revealed a significant endorsement of supernatural causation. Logistic regressions revealed significant contributions of old age and female gender to supernatural attribution; old age, high education and Catholic religious denomination to psychosocial attributions; and high education to biological attributions.
Conclusions:
It is hoped that the findings would enlighten, augment literature and enhance mental health care service delivery
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