265 research outputs found
On the origin of magnetoresistance in SrFeMoO
We report detailed magnetization () and magnetoresistance () studies
on a series of SrFeMoO samples with independent control on anti-site
defect and grain boundary densities. These results, exhibiting a switching-like
behavior of with , establish that the is controlled by the
magnetic polarization of grain boundary regions, rather than of the grains
within a resonant tunnelling mechanism.Comment: 4 pages, 4 figure
Understanding the bulk electronic structure of Ca1-xSrxVO3
We investigate the electronic structure of Ca1-xSrxVO3 using careful
state-of-the-art experiments and calculations. Photoemission spectra using
synchrotron radiation reveal a hitherto unnoticed polarization dependence of
the photoemission matrix elements for the surface component leading to a
substantial suppression of its intensity. Bulk spectra extracted with the help
of experimentally determined electron escape depth and estimated suppression of
surface contributions resolve outstanding puzzles concerning the electronic
structure in Ca1-xSrxVO3.Comment: 4 pages including 3 figure
Electron-spectroscopic investigation of metal-insulator transition in Sr2Ru1-xTixO4 (x=0.0-0.6)
We investigate the nature and origin of the metal-insulator transition in
Sr2Ru1-xTixO4 as a function of increasing Ti content (x). Employing detailed
core, valence, and conduction band studies with x-ray and ultraviolet
photoelectron spectroscopies along with Bremsstrahlung isochromat spectroscopy,
it is shown that a hard gap opens up for Ti content greater than equal to 0.2,
while compositions with x<0.2 exhibit finite intensity at the Fermi energy.
This establishes that the metal-insulator transition in this homovalent
substituted series of compounds is driven by Coulomb interaction leading to the
formation of a Mott gap, in contrast to transitions driven by disorder effects
or band flling.Comment: Accepted for publication in Phys. Rev.
Origin of magnetic moments and presence of a resonating valence bond state in BaYIrO
While it was speculated that 5 systems would possess non-magnetic
~=~0 ground state due to strong Spin-Orbit Coupling (SOC), all such systems
have invariably shown presence of magnetic moments so far. A puzzling case is
that of BaYIrO, which in spite of having a perfectly cubic structure
with largely separated Ir () ions, has consistently shown presence
of weak magnetic moments. Moreover, we clearly show from Muon Spin Relaxation
(SR) measurements that a change in the magnetic environment of the
implanted muons in BaYIrO occurs as temperature is lowered below 10~K.
This observation becomes counterintuitive, as the estimated value of SOC
obtained by fitting the RIXS spectrum of BaYIrO with an atomic
model is found to be as high as 0.39~eV, meaning that the system within this
model is neither expected to possess moments nor exhibit temperature dependent
magnetic response. Therefore we argue that the atomic coupling
description is not sufficient to explain the ground state of such systems,
where despite having strong SOC, presence of hopping triggers delocalisation of
holes, resulting in spontaneous generation of magnetic moments. Our theoretical
calculations further indicate that these moments favour formation of
spin-orbital singlets in the case of BaYIrO, which is manifested in
SR experiments measured down to 60~mK.Comment: 20 Pages, 7 Figure
A microspectroscopic study of the electronic homogeneity of ordered and disordered Sr2FeMoO6
Besides a drastic reduction in saturation magnetization of disordered
Sr2FeMoO6 compared to highly ordered samples, magnetizations as a function of
the temperature for different disordered samples may also show qualitatively
different behaviors. We investigate the origin of such diversity by performing
spatially resolved photoemission spectroscopy on various disordered samples.
Our results establish that extensive electronic inhomogeneity, arising most
probably from an underlying chemical inhomogeneity in disordered samples is
responsible for the observed magnetic inhomogeneity. It is further pointed out
that these inhomogeneities are connected with composition fluctuations of the
type Sr2Fe1+xMo1-xO6 with Fe-rich (x>0) and Mo-rich (x<0) regions.Comment: 14 pages, 4 figure
Electronic Structure of Sr_2FeMoO_6
We have analysed the unusual electronic structure of Sr_2FeMoO_6 combining
ab-initio and model Hamiltonian approaches. Our results indicate that there are
strong enhancements of the intraatomic exchange strength at the Mo site as well
as the antiferromagnetic coupling strength between Fe and Mo sites. We discuss
the possibility of a negative effective Coulomb correlation strength (U_{eff})
at the Mo site due to these renormalised interaction strengths.Comment: To appear in Phys. Rev. Let
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