2,738 research outputs found
Ground state magnetic structure of MnGe
We have used spherical neutron polarimetry to investigate the magnetic
structure of the Mn spins in the hexagonal semimetal MnGe, which exhibits a
large intrinsic anomalous Hall effect. Our analysis of the polarimetric data
finds a strong preference for a spin structure with symmetry relative
to the point group. We show that weak ferromagnetism is an inevitable
consequence of the symmetry of the observed magnetic structure, and that sixth
order anisotropy is needed to select a unique ground state
A model for spin-polarized transport in perovskite manganite bi-crystal grain boundaries
We have studied the temperature dependence of low-field magnetoresistance and
current-voltage characteristics of a low-angle bi-crystal grain boundary
junction in perovskite manganite La_{2/3}Sr_{1/3}MnO_3 thin film. By gradually
trimming the junction we have been able to reveal the non-linear behavior of
the latter. With the use of the relation M_{GB} \propto M_{bulk}\sqrt{MR^*} we
have extracted the grain boundary magnetization. Further, we demonstrate that
the built-in potential barrier of the grain boundary can be modelled by
V_{bi}\propto M_{bulk}^2 - M_{GB}^2. Thus our model connects the
magnetoresistance with the potential barrier at the grain boundary region. The
results indicate that the band-bending at the grain boundary interface has a
magnetic origin.Comment: 9 pages, 5 figure
Mesoscopic Phase Coherence in a Quantum Spin Fluid
Mesoscopic quantum phase coherence is important because it improves the
prospects for handling quantum degrees of freedom in technology. Here we show
that the development of such coherence can be monitored using magnetic neutron
scattering from a one-dimensional spin chain Y2BaNiO5, a quantum spin fluid
where no classical, static magnetic order is present. In the cleanest samples,
the quantum coherence length is 20 nm, almost an order of magnitude larger than
the classical antiferromagnetic correlation length of 3 nm. We also demonstrate
that the coherence length can be modified by static and thermally activated
defects in a quantitatively predictable manner
Kinetic Study on Heavy Metal Divalent Ions Removal using Zirconium-Based Magnetic Sorbent
In this research, zirconium-based magnetic sorbent synthesised by chemical co-precipitation method is explored as a potential sorbent for removal of divalent metal ions from aqueous solution. The interaction characteristics between the ions and the sorbent were elucidated by instrumental analyses such as Fourier Transform InfraRed (FT-IR) Spectroscopy, Scanning Electron Microscopy (SEM), and Brunauer, Emmett, and Teller (BET) surface area analyser. Results show that the sorption rate was increased with an increase in contact time and initial metal ion concentration. Moreover, a two-stage kinetics behaviour was observed, and all the batch experiments achieved an equilibrium state within 4 hours. The evaluation of the adsorption behaviour of heavy metal divalent ions onto the magnetic sorbent was explained using two kinetic models, and it was mostly found to follow the postulate of the pseudo-second-order kinetic model. The validity of kinetic models applied in this study is also evaluated by using a normalised standard deviation
Mesoscale magnetism at the grain boundaries in colossal magnetoresistive films
We report the discovery of mesoscale regions with distinctive magnetic
properties in epitaxial LaSrMnO films which exhibit
tunneling-like magnetoresistance across grain boundaries. By using
temperature-dependent magnetic force microscopy we observe that the mesoscale
regions are formed near the grain boundaries and have a different Curie
temperature (up to 20 K {\it higher}) than the grain interiors. Our images
provide direct evidence for previous speculations that the grain boundaries in
thin films are not magnetically and electronically sharp interfaces. The size
of the mesoscale regions varies with temperature and nature of the underlying
defect.Comment: 4 pages of text, 4 figure
Compact circularly polarized truncated square ring slot antenna with suppressed higher resonances
This paper presents a compact circularly polarized (CP) antenna with an integrated higher order harmonic rejection filter. The proposed design operates within the ISM band of 2.32 GHz± 2.63 GHz and is suitable for example for wireless power transfer applications. Asymmetrical truncated edges on a square ring create a defected ground structure to excite the CP property, simultaneously realizing compactness. It offers a 50.5% reduced patch area compared to a conventional design. Novel stubs and slot shapes are integrated in the transmission line to reduce higher (up to the third) order harmonics. The proposed prototype yields a -10 dB reflection coefficient (S11) impedance bandwidth of 12.53%, a 3 dB axial ratio bandwidth of 3.27%, and a gain of 5.64 dBi. Measurements also show good agreement with simulations. © 2017 Sabran et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Disorder, pseudospins, and backscattering in carbon nanotubes
We address the effects of disorder on the conducting properties of metal and
semiconducting carbon nanotubes. Experimentally, the mean free path is found to
be much larger in metallic tubes than in doped semiconducting tubes. We show
that this result can be understood theoretically if the disorder potential is
long-ranged. The effects of a pseudospin index that describes the internal
sublattice structure of the states lead to a suppression of scattering in
metallic tubes, but not in semiconducting tubes. This conclusion is supported
by tight-binding calculations.Comment: four page
Substrate-induced strain effects on Pr_{0.6}Ca_{0.4}MnO_{3} films
We report the characterization of the crystal structure, low-temperature
charge and orbital ordering, transport, and magnetization of
Pr_{0.6}Ca_{0.4}MnO_{3} films grown on LaAlO_{3}, NdGaO_{3}, and SrTiO_{3}
substrates, which provide compressive (LaAlO_{3}) and tensile (NdGaO_{3} and
SrTiO_{3}) strain. The films are observed to exhibit different crystallographic
symmetries than the bulk material, and the low-temperature ordering is found to
be more robust under compressive-- as opposed to tensile-- strain. In fact,
bulk-like charge and orbital ordering is not observed in the film grown on
NdGaO_{3}, which is the substrate that provides the least amount of nominal and
measured, but tensile, strain. This result suggests the importance of the role
played by the Mn--O--Mn bond angles in the formation of charge and orbital
ordering at low temperatures. Finally, in the film grown on LaAlO_{3}, a
connection between the lattice distortion associated with orbital ordering and
the onset of antiferromagnetism is reported.Comment: 12 pages, 7 figure
Coupling of magnetic order and charge transport in the candidate Dirac semimetal EuCdAs
We use resonant elastic x-ray scattering to determine the evolution of
magnetic order in EuCdAs below \,K, as a function of
temperature and applied magnetic field. We find an A-type
antiferromagneticstructure with in-plane magnetic moments, and observe dramatic
magnetoresistive effects associated with field-induced changes in the magnetic
structure and domain populations. Our \textit{ab initio} electronic structure
calculations indicate that the Dirac dispersion found in the nonmagnetic Dirac
semimetal CdAs is also present in EuCdAs, but is gapped for due to the breaking of symmetry by the magnetic
structure.Comment: Supplemental information attached to preprin
Atomic-scale images of charge ordering in a mixed-valence manganite
Transition-metal perovskite oxides exhibit a wide range of extraordinary but
imperfectly understood phenomena. Charge, spin, orbital, and lattice degrees of
freedom all undergo order-disorder transitions in regimes not far from where
the best-known of these phenomena, namely high-temperature superconductivity of
the copper oxides, and the 'colossal' magnetoresistance of the manganese
oxides, occur. Mostly diffraction techniques, sensitive either to the spin or
the ionic core, have been used to measure the order. Unfortunately, because
they are only weakly sensitive to valence electrons and yield superposition of
signals from distinct mesoscopic phases, they cannot directly image mesoscopic
phase coexistence and charge ordering, two key features of the manganites. Here
we describe the first experiment to image charge ordering and phase separation
in real space with atomic-scale resolution in a transition metal oxide. Our
scanning tunneling microscopy (STM) data show that charge order is correlated
with structural order, as well as with whether the material is locally metallic
or insulating, thus giving an atomic-scale basis for descriptions of the
manganites as mixtures of electronically and structurally distinct phases.Comment: 8 pages, 4 figures, 19 reference
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