449 research outputs found
Spin/orbit moment imbalance in the near-zero moment ferromagnetic semiconductor SmN
SmN is ferromagnetic below 27 K, and its net magnetic moment of 0.03 Bohr
magnetons per formula unit is one of the smallest magnetisations found in any
ferromagnetic material. The near-zero moment is a result of the nearly equal
and opposing spin and orbital moments in the 6H5/2 ground state of the Sm3+
ion, which leads finally to a nearly complete cancellation for an ion in the
SmN ferromagnetic state. Here we explore the spin alignment in this compound
with X-ray magnetic circular dichroism at the Sm L2,3 edges. The spectral
shapes are in qualitative agreement with computed spectra based on an LSDA+U
(local spin density approximation with Hubbard-U corrections) band structure,
though there remain differences in detail which we associate with the anomalous
branching ratio in rare-earth L edges. The sign of the spectra determine that
in a magnetic field the Sm 4f spin moment aligns antiparallel to the field; the
very small residual moment in ferromagnetic SmN aligns with the 4f orbital
moment and antiparallel to the spin moment. Further measurements on very thin
(1.5 nm) SmN layers embedded in GdN show the opposite alignment due to a strong
Gd-Sm exchange, suggesting that the SmN moment might be further reduced by
about 0.5 % Gd substitution
Europium nitride: A novel diluted magnetic semiconductor
Europium nitride is semiconducting and contains non-magnetic \3+, but
sub-stoichiometric EuN has Eu in a mix of 2+ and 3+ charge states. We show that
at \2+ ~concentrations near 15-20% EuN is ferromagnetic with a Curie
temperature as high as 120 K. The \3+ ~polarization follows that of the \2+,
confirming that the ferromagnetism is intrinsic to the EuN which is thus a
novel diluted magnetic semiconductor. Transport measurements shed light on the
likely exchange mechanisms.Comment: 5 page
Ferromagnetic redshift of the optical gap in GdN
We report measurements of the optical gap in a GdN film at temperatures from
300 to 6K, covering both the paramagnetic and ferromagnetic phases. The gap is
1.31eV in the paramagnetic phase and red-shifts to 0.9eV in the spin-split
bands below the Curie temperature. The paramagnetic gap is larger than was
suggested by very early experiments, and has permitted us to refine a
(LSDA+U)-computed band structure. The band structure was computed in the full
translation symmetry of the ferromagnetic ground state, assigning the
paramagnetic-state gap as the average of the majority- and minority-spin gaps
in the ferromagnetic state. That procedure has been further tested by a band
structure in a 32-atom supercell with randomly-oriented spins. After fitting
only the paramagnetic gap the refined band structure then reproduces our
measured gaps in both phases by direct transitions at the X point.Comment: 5 pages, 4 figure
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Influence of chemical interactions on the electronic properties of BiOI/organic semiconductor heterojunctions for application in solution-processed electronics
Bismuth oxide iodide (BiOI) has been viewed as a suitable environmentally-friendly alternative to lead-halide perovskites for low-cost (opto-)electronic applications such as photodetectors, phototransistors and sensors. To enable its incorporation in these devices in a convenient, scalable, and economical way, BiOI thin films were investigated as part of heterojunctions with various p-type organic semiconductors (OSCs) and tested in a field-effect transistor (FET) configuration. The hybrid heterojunctions, which combine the respective functionalities of BiOI and the OSCs were processed from solution under ambient atmosphere. The characteristics of each of these hybrid systems were correlated with the physical and chemical properties of the respective materials using a concept based on heteropolar chemical interactions at the interface. Systems suitable for application in lateral transport devices were identified and it was demonstrated how materials in the hybrids interact to provide improved and synergistic properties. These indentified heterojunction FETs are a first instance of successful incorporation of solution-processed BiOI thin films in a three-terminal device. They show a significant threshold voltage shift and retained carrier mobility compared to pristine OSC devices and open up possibilities for future optoelectronic applications
Surface states and Rashba-type spin polarization in antiferromagnetic MnBiTe
The layered van der Waals antiferromagnet MnBiTe has been predicted
to combine the band ordering of archetypical topological insulators such as
BiTe with the magnetism of Mn, making this material a viable candidate
for the realization of various magnetic topological states. We have
systematically investigated the surface electronic structure of
MnBiTe(0001) single crystals by use of spin- and angle-resolved
photoelectron spectroscopy experiments. In line with theoretical predictions,
the results reveal a surface state in the bulk band gap and they provide
evidence for the influence of exchange interaction and spin-orbit coupling on
the surface electronic structure.Comment: Revised versio
Vortex dynamics in layered superconductors with correlated defects: influence of interlayer coupling
We report a detailed study of the vortex dynamics and vortex phase diagrams
of two amorphous Ta_0.3Ge_0.7/Ge multilayered films with intrinsic coplanar
defects, but different interlayer coupling. A pinned Bose-glass phase in the
more weakly coupled sample exists only below a cross-over field H* in striking
contrast to the strongly coupled film. Above H* the flux lines are thought to
break up into pancake vortices and the cross-over field is significantly
increased when the field is aligned along the extended defects. The two films
show different vortex creep excitations in the Bose-glass phase.Comment: zip file: 1 RevTex, 5 figures (png
An examination of the effects of self-regulatory focus on the perception of the media richness: the case of email
Communication is a key element in organizations’ business success. The media richness theory and the channel expansion theory are two of the most influential theories regarding the selection and use of communication media in organizations; however, literature has focused little on the effects of self-regulation by managers and employees in these theories. To analyze these topics, this study develops an empirical investigation by gathering data from 600 managers and employees using a questionnaire. The results suggest that the perception of media richness is positively affected when the individual shows a promotion focus or strategy.Peer ReviewedPostprint (author’s final draft
Single phase nanocrystalline GaMnN thin films with high Mn content
Ga₁ˍₓ Mnₓ Nthin films with a Mn content as high as x=0.18 have been grown using ion-assisted deposition and a combination of Rutherford backscattering spectroscopy and nuclear reaction analysis was used to determine their composition. The structure of the films was determined from x-ray diffraction,transmission electron microscopy, and extended x-ray absorption fine structure(EXAFS). The films are comprised of nanocrystals of random stacked GaMnN and there is no evidence of Mn-rich secondary phases or clusters. EXAFS measurements at the Mn and Ga edge are almost identical to those at the Ga edge from Mn-free nanocrystallineGaNfilms, showing that the Mn occupies the Ga lattice sites, and simulated radial distribution functions of possible Mn-rich impurity phases bear no resemblance to the experimental data. The results indicate that these are the most heavily Mn-doped single phase GaNfilms studied to date.The authors gratefully acknowledge financial support
from the New Zealand Foundation for Research Science and
Technology through its New Economy Research Fund, and
through a postdoctoral fellowship of one of the authors
B.J.R.. The work of the MacDiarmid Institute is supported
by a New Zealand Centre of Research Excellence award.
Another author S.G. wishes to thank Education New
Zealand for financial support of the EXAFS measurements
The unusual electronic structure of the "pseudo-ladder" compound CaCu2O3
Experimental and theoretical studies of the unoccupied electronic structure
of CaCu2O3 single crystals have been performed using polarization-dependent
x-ray absorption spectroscopy and band structure calculations. The measured
hole distribution shows an unusual large number of holes in orbitals parallel
to the interlayer direction which is in agreement with the theoretical
analysis. CaCu2O3 deviates significantly from the standard pd-sigma cuprate
picture. The corresponding strong interlayer exchange is responsible for the
missing spin gap generic for other two-leg ladder cuprates.Comment: 4 pages, 3 figures include
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