2,476 research outputs found
Magnitude and crystalline anisotropy of hole magnetization in (Ga,Mn)As
Theory of hole magnetization Mc in zinc-blende diluted ferromagnetic
semiconductors is developed relaxing the spherical approximation of earlier
approaches. The theory is employed to determine Mc for (Ga,Mn)As over a wide
range of hole concentrations and a number of crystallographic orientations of
Mn magnetization. It is found that anisotropy of Mc is practically negligible
but the obtained magnitude of Mc is significantly greater than that determined
in the spherical approximation. Its sign and value compares favorably with the
results of available magnetization measurements and ferromagnetic resonance
studies.Comment: 5 pages, 3 figure
Origin of ferromagnetism in (Zn,Co)O from magnetization and spin-dependent magnetoresistance
In order to elucidate the nature of ferromagnetic signatures observed in
(Zn,Co)O we have examined experimentally and theoretically magnetic properties
and spin-dependent quantum localization effects that control low-temperature
magnetoresistance. Our findings, together with a through structural
characterization, substantiate the model assigning spontaneous magnetization of
(Zn,Co)O to uncompensated spins at the surface of antiferromagnetic nanocrystal
of Co-rich wurtzite (Zn,Co)O. The model explains a large anisotropy observed in
both magnetization and magnetoresistance in terms of spin hamiltonian of Co
ions in the crystal field of the wurtzite lattice.Comment: 6 pages, 6 figure
Anomalous Hall effect in field-effect structures of (Ga,Mn)As
The anomalous Hall effect in metal-insulator-semiconductor structures having
thin (Ga,Mn)As layers as a channel has been studied in a wide range of Mn and
hole densities changed by the gate electric field. Strong and unanticipated
temperature dependence, including a change of sign, of the anomalous Hall
conductance has been found in samples with the highest Curie
temperatures. For more disordered channels, the scaling relation between
and , similar to the one observed previously for
thicker samples, is recovered.Comment: 5 pages, 5 figure
Magnetic domains in III-V magnetic semiconductors
Recent progress in theoretical understanding of magnetic anisotropy and
stiffness in III-V magnetic semiconductors is exploited for predictions of
magnetic domain characteristics and methods of their tuning. We evaluate the
width and the energy of domain walls as well as the period of stripe domains in
perpendicular films. The computed stripe width d = 1.1 um for
Ga_0.957Mn_0.043As/In_0.16Ga_0.84As compares favorably to the experimental
value 1.5 um, as determined by Shono et al. [Appl. Phys. Lett. 77, 1363
(2000)].Comment: 4 RevTex pages, 2 figures spelling of author's names corrected in
abstract pag
Spin-related magnetoresistance of n-type ZnO:Al and Zn_{1-x}Mn_{x}O:Al thin films
Effects of spin-orbit coupling and s-d exchange interaction are probed by
magnetoresistance measurements carried out down to 50 mK on ZnO and
Zn_{1-x}Mn_{x}O with x = 3 and 7%. The films were obtained by laser ablation
and doped with Al to electron concentration ~10^{20} cm^{-3}. A quantitative
description of the data for ZnO:Al in terms of weak-localization theory makes
it possible to determine the coupling constant \lambda_{so} = (4.4 +-
0.4)*10^{-11} eVcm of the kp hamiltonian for the wurzite structure, H_{so} =
\lambda_{so}*c(s x k). A complex and large magnetoresistance of
Zn_{1-x}Mn_{x}O:Al is interpreted in terms of the influence of the s-d
spin-splitting and magnetic polaron formation on the disorder-modified
electron-electron interactions. It is suggested that the proposed model
explains the origin of magnetoresistance observed recently in many magnetic
oxide systems.Comment: 4 pages, 4 figure
Prospect for room temperature tunneling anisotropic magnetoresistance effect: density of states anisotropies in CoPt systems
Tunneling anisotropic magnetoresistance (TAMR) effect, discovered recently in
(Ga,Mn)As ferromagnetic semiconductors, arises from spin-orbit coupling and
reflects the dependence of the tunneling density of states in a ferromagnetic
layer on orientation of the magnetic moment. Based on ab initio relativistic
calculations of the anisotropy in the density of states we predict sizable TAMR
effects in room-temperature metallic ferromagnets. This opens prospect for new
spintronic devices with a simpler geometry as these do not require
antiferromagnetically coupled contacts on either side of the tunnel junction.
We focus on several model systems ranging from simple hcp-Co to more complex
ferromagnetic structures with enhanced spin-orbit coupling, namely bulk and
thin film L1-CoPt ordered alloys and a monatomic-Co chain at a Pt surface
step edge. Reliability of the predicted density of states anisotropies is
confirmed by comparing quantitatively our ab initio results for the
magnetocrystalline anisotropies in these systems with experimental data.Comment: 4 pages, 2 figure
Optical properties of metallic (III,Mn)V ferromagnetic semiconductors in the infrared to visible range
We report on a study of the ac conductivity and magneto-optical properties of
metallic ferromagnetic (III,Mn)V semiconductors in the infrared to visible
spectrum. Our analysis is based on the successful kinetic exchange model for
(III,Mn)V ferromagnetic semiconductors. We perform the calculations within the
Kubo formalism and treat the disorder effects pertubatively within the Born
approximation, valid for the metallic regime. We consider an eight-band
Kohn-Luttinger model (six valence bands plus two conduction bands) as well as a
ten-band model with additional dispersionless bands simulating
phenomenologically the upper-mid-gap states induced by antisite and
interstitial impurities. These models qualitatively account for
optical-absorption experiments and predict new features in the mid-infrared
Kerr angle and magnetic-circular-dichroism properties as a function of Mn
concentration and free carrier density.Comment: 10 pages, 7 figures, some typos correcte
Self-sustained magnetoelectric oscillations in magnetic resonant tunneling structures
The dynamic interplay of transport, electrostatic, and magnetic effects in
the resonant tunneling through ferromagnetic quantum wells is theoretically
investigated. It is shown that the carrier-mediated magnetic order in the
ferromagnetic region not only induces, but also takes part in intrinsic,
robust, and sustainable high-frequency current oscillations over a large window
of nominally steady bias voltages. This phenomenon could spawn a new class of
quantum electronic devices based on ferromagnetic semiconductors.Comment: 5 pages, 4 figure
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