9,021 research outputs found
Clustering induced suppression of ferromagnetism in diluted magnets
Ferromagnetism in diluted magnets in the compensated regime p << x is shown
to be suppressed by the formation of impurity spin clusters. The majority bulk
spin couplings are shown to be considerably weakened by the preferential
accumulation of holes in spin clusters, resulting in low-energy magnon
softening and enhanced low-temperature decay of magnetic order. A locally
self-consistent magnon renormalization analysis of spin dynamics shows that
although strong intra-cluster correlations tend to prolong global order, T_c is
still reduced compared to the ordered case.Comment: published version, 5 pages, 4 figure
The Influence of Magnetic Domain Walls on Longitudinal and Transverse Magnetoresistance in Tensile Strained (Ga,Mn)As Epilayers
We present a theoretical analysis of recent experimental measurements of
magnetoresistance in (Ga,Mn)As epilayers with perpendicular magnetic
anisotropy. The model reproduces the field-antisymmetric anomalies observed in
the longitudinal magnetoresistance in the planar geometry (magnetic field in
the epilayer plane and parallel to the current density), as well as the unusual
shape of the accompanying transverse magnetoresistance. The magnetoresistance
characteristics are attributed to circulating currents created by the presence
of magnetic domain walls
Anisotropic Electrical Spin Injection in Ferromagnetic Semiconductor Heterostructures
A fourteen-fold anisotropy in the spin transport efficiency parallel and
perpendicular to the charge transport is observed in a vertically-biased
(Ga,Mn)As-based spin-polarized light emitting diode. The spin polarization is
determined by measuring the polarization of electroluminescence from an
(In,Ga)As quantum well placed a distance d (20 to 420 nm) below the p-type
ferromagnetic (Ga,Mn)As contact. In addition, a monotonic increase from 0.5 to
7% in the polarization is measured as d decreases for collection parallel to
the growth direction, while the in-plane polarization from the perpendicular
direction (~0.5%) remains unchanged.Comment: 11 pages, 3 figures, to be published, Applied Physics Letters, March
11, 200
Velocity of domain-wall motion induced by electrical current in a ferromagnetic semiconductor (Ga,Mn)As
Current-induced domain-wall motion with velocity spanning over five orders of
magnitude up to 22 m/s has been observed by magneto-optical Kerr effect in
(Ga,Mn)As with perpendicular magnetic anisotropy. The data are employed to
verify theories of spin-transfer by the Slonczewski-like mechanism as well as
by the torque resulting from spin-flip transitions in the domain-wall region.
Evidence for domain-wall creep at low currents is found.Comment: 5 pages, 3 figure
Light and electric field control of ferromagnetism in magnetic quantum structures
A strong influence of illumination and electric bias on the Curie temperature
and saturation value of the magnetization is demonstrated for semiconductor
structures containing a modulation-doped p-type Cd0.96Mn0.04Te quantum well
placed in various built-in electric fields. It is shown that both light beam
and bias voltage generate an isothermal and reversible cross-over between the
paramagnetic and ferromagnetic phases, in the way that is predetermined by the
structure design. The observed behavior is in quantitative agreement with the
expectations for systems, in which ferromagnetic interactions are mediated by
the weakly disordered two-dimensional hole liquid.Comment: 4 pages and 3 figure
Integral Transforms for Conformal Field Theories with a Boundary
A new method is developed for solving the conformally invariant integrals
that arise in conformal field theories with a boundary. The presence of a
boundary makes previous techniques for theories without a boundary less
suitable. The method makes essential use of an invertible integral transform,
related to the radon transform, involving integration over planes parallel to
the boundary. For successful application of this method several nontrivial
hypergeometric function relations are also derived.Comment: 20 pagess, LateX fil
A Gate-Induced Switch in Zigzag Graphene Naoribbons and Charging Effects
Using non-equilibrium Green's function formalism, we investigate nonlinear
transport and charging effects of gated graphene nanoribbons (GNRs) with even
number of zigzag chains. We find a negative differential resistance (NDR) over
a wide range of gate voltages with on/off ratio for narrow enough
ribbons. This NDR originates from the parity selection rule and also
prohibition of transport between discontinues energy bands. Since the external
field is well screened close to the contacts, the NDR is robust against the
electrostatic potential. However, for voltages higher than the NDR threshold,
due to charge transfer through the edges of ZGNR, screening is reduced such
that the external potential can penetrate inside the ribbon giving rise to
smaller values of off current. Furthermore, on/off ratio of the current depends
on the aspect ratio of the length/width and also edge impurity. Moreover,
on/off ratio displays a power law behavior as a function of ribbon length.Comment: 8 pages, 9 figure
Quantum Dot as Spin Filter and Spin Memory
We consider a quantum dot in the Coulomb blockade regime weakly coupled to
current leads and show that in the presence of a magnetic field the dot acts as
an efficient spin-filter (at the single-spin level) which produces a
spin-polarized current. Conversely, if the leads are fully spin-polarized the
up or down state of the spin on the dot results in a large sequential or small
cotunneling current, and thus, together with ESR techniques, the setup can be
operated as a single-spin memory.Comment: 4 pages, 3 figures, REVTe
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