816 research outputs found
Depth profile photoemission study of thermally diffused Mn/GaAs (001) interfaces
We have performed a depth profile study of thermally diffused Mn/GaAs (001)
interfaces using photoemission spectroscopy combined with Ar-ion
sputtering. We found that Mn ion was thermally diffused into the deep region of
the GaAs substrate and completely reacted with GaAs. In the deep region, the Mn
2 core-level and Mn 3 valence-band spectra of the Mn/GaAs (001) sample
heated to 600 C were similar to those of GaMnAs,
zinc-blende-type MnAs dots, and/or interstitial Mn in tetrahedrally coordinated
by As atoms, suggesting that the Mn 3 states were essentially localized but
were hybridized with the electronic states of the host GaAs. Ferromagnetism was
observed in the dilute Mn phase.Comment: 5 pages, 4 figure
Combined approach of density functional theory and quantum Monte Carlo method to electron correlation in dilute magnetic semiconductors
We present a realistic study for electronic and magnetic properties in dilute
magnetic semiconductor (Ga,Mn)As. A multi-orbital Haldane-Anderson model
parameterized by density-functional calculations is presented and solved with
the Hirsch-Fye quantum Monte Carlo algorithm. Results well reproduce
experimental results in the dilute limit. When the chemical potential is
located between the top of the valence band and an impurity bound state, a
long-range ferromagnetic correlations between the impurities, mediated by
antiferromagnetic impurity-host couplings, are drastically developed. We
observe an anisotropic character in local density of states at the
impurity-bound-state energy, which is consistent with the STM measurements. The
presented combined approach thus offers a firm starting point for realistic
calculations of the various family of dilute magnetic semiconductors.Comment: 5 pages, 4 figure
Correlated defects, metal-insulator transition, and magnetic order in ferromagnetic semiconductors
The effect of disorder on transport and magnetization in ferromagnetic III-V
semiconductors, in particular (Ga,Mn)As, is studied theoretically. We show that
Coulomb-induced correlations of the defect positions are crucial for the
transport and magnetic properties of these highly compensated materials. We
employ Monte Carlo simulations to obtain the correlated defect distributions.
Exact diagonalization gives reasonable results for the spectrum of valence-band
holes and the metal-insulator transition only for correlated disorder. Finally,
we show that the mean-field magnetization also depends crucially on defect
correlations.Comment: 4 pages RevTeX4, 5 figures include
Single-Band Model for Diluted Magnetic Semiconductors: Dynamical and Transport Properties and Relevance of Clustered States
Dynamical and transport properties of a simple single-band spin-fermion
lattice model for (III,Mn)V diluted magnetic semiconductors (DMS) is here
discussed using Monte Carlo simulations. This effort is a continuation of
previous work (G. Alvarez, Phys. Rev. Lett. 89, 277202 (2002)) where the static
properties of the model were studied. The present results support the view that
the relevant regime of J/t (standard notation) is that of intermediate
coupling, where carriers are only partially trapped near Mn spins, and locally
ordered regions (clusters) are present above the Curie temperature T_C. This
conclusion is based on the calculation of the resistivity vs. temperature, that
shows a soft metal to insulator transition near T_C, as well on the analysis of
the density-of-states and optical conductivity. In addition, in the clustered
regime a large magnetoresistance is observed in simulations. Formal analogies
between DMS and manganites are also discussed.Comment: Revtex4, 20 figures. References updated, minor changes to figures and
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JSPS-7 Bovine Respiratory Syncytial Virus Infection Enhances Pasteurella multocida Adherence on Respiratory Epithelial Cells
Bovine respiratory syncytial virus (BRSV) is a single negative-stranded RNA virus belonging to the Paramyxoviridae family and shows a close genetic relationship with human respiratory syncytial virus (HRSV). BRSV is the primary etiological agent of respiratory disease in calves aged up to 12 months [1]; beef and dairy cattle worldwide [2, 3]. Initial infection by BRSV alter bovine immune system and facilitates secondary infection of the lower respiratory tract by bacteria [1, 4]. Therefore, BRSV is considered to be a causative agent of bovine respiratory disease complex, which results in economic losses to farmers because of the morbidity and mortality in cattle [2, 3]. According to our preliminary findings based on the gene detection from respiratory samples, paired virus and bacteria were detected; Pasteurella multocida (PM) was the most common bacterial agent (unpublished data). PM is common in the nasopharynx of cattle [5, 6], although PM appears to be part of the normal flora, it can contribute to pneumonia when cattle stressed and/or infected by a respiratory virus [7]. However, the interactions between multiple agents associated with BRDC are not clear. Therefore, the aim of this study was to investigate the effect of BRSV infection on PM adherence to respiratory epithelial cells
Effect of Intensive Insulin Therapy Using a Closed-Loop Glycemic Control System in Hepatic Resection Patients: A prospective randomized clinical trial
Ferromagnetism in magnetically doped III-V semiconductors
The origin of ferromagnetism in semimagnetic III-V materials is discussed.
The indirect exchange interaction caused by virtual electron excitations from
magnetic impurity level in the bandgap to the valence band can explain
ferromagnetism in GaAs(Mn) no matter samples are degenerated or not. Formation
of ferromagnetic clusters and percolation picture of phase transition describes
well all available experimental data and allows to predict the Mn-composition
dependence of transition temperature in wurtzite (Ga,In,Al)N epitaxial layers.Comment: 4 pages with 3 figure
Spin interactions of interstitial Mn ions in ferromagnetic GaMnAs
The recently reported Rutherford backscattering and particle-induced X-ray
emission experiments have revealed that in low-temperature MBE grown GaMnAs a
significant part of the incorporated Mn atoms occupies tetrahedral interstitial
sites in the lattice. Here we study the magnetic properties of these
interstitial ions. We show that they do not participate in the hole-induced
ferromagnetism. Moreover, Mn interstitial double donors may form pairs with the
nearest substitutional Mn acceptors - our calculations evidence that the spins
in such pairs are antiferromagnetically coupled by the superexchange. We also
show that for the Mn ion in the other, hexagonal, interstitial position (which
seems to be the case in the GaMnBeAs samples) the p-d interactions with the
holes, responsible for the ferromagnetism, are very much suppressed.Comment: 4 pages, 3 figures, submitted to PR
Hole spin polarization in GaAlAs:Mn structures
A self-consistent calculation of the electronic properties of GaAlAs:Mn
magnetic semiconductor quantum well structures is performed including the
Hartree term and the sp-d exchange interaction with the Mn magnetic moments.
The spin polarization density is obtained for several structure configurations.
Available experimental results are compared with theory.Comment: 4 page
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