6,882 research outputs found
A new class of magnetic materials: Sr2FeMoO6 and related compounds
Ordered double perovskite oxides of the general formula, A2BB'O6, have been
known for several decades to have interesting electronic and magnetic
properties. However, a recent report of a spectacular negative
magnetoresistance effect in a specific member of this family, namely Sr2FeMoO6,
has brought this class of compounds under intense scrutiny. It is now believed
that the origin of magnetism in this class of compounds is based on a novel
kinetically-driven mechanism. This new mechanism is also likely to be
responsible for the unusually high temperature ferromagnetism in several other
systems, such as dilute magnetic semiconductors, as well as in various
half-metallic ferromagnetic systems, such as Heussler alloys.Comment: To appear in Current Opinion in Solid State and Material Scienc
Spin, charge and orbital ordering in La0.5Sr1.5MnO4
We have analyzed the experimental evidence of charge and orbital ordering in
La0.5Sr1.5MnO4 using first principles band structure calculations. Our results
suggest the presence of two types of Mn sites in the system. One of the Mn
sites behaves like an Mn(3+) ion, favoring a Jahn-Teller distortion of the
surrounding oxygen atoms, while the distortion around the other is not a simple
breathing mode kind. Band structure effects are found to dominate the
experimental spectrum for orbital and charge ordering, providing an alternate
explanation for the experimentally observed results.Comment: 4 pages + 3 figures; To appear in Phys. Rev. Let
Remarkable thermal stability of BF3-doped polyaniline
We show that the recently synthesized BF3-doped polyaniline (PANI) exhibits
remarkable stability against thermal ageing. Unlike the protonated PANI, which
shows rapid degradation of the conductivity on heating in air, BF3-doped PANI
shows more than an order of magnitude improvement in conductivity. We employ
x-ray photoelectron spectroscopy (XPS), fourier transform infra-red (FTIR)
spectroscopy, and x-ray diffraction (XRD) to understand this unexpected
phenomenon.Comment: 4 pages and 3 figures. To appear in Applied Physics Letters, Sept.
200
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
Origin of Ferromagnetism and its pressure and doping dependence in TlMnO
Using NMTO-{\it downfolding} technique, we explore and establish the origin
of ferromagnetism in the pyrochlore system, TlMnO. It is
found to be driven by hybridization induced spin-polarization of the
delocalized charge carriers derived from Tl- and O- states. The
mean-field estimate of the ferromagnetic transition temperature, T,
estimated using computed exchange integrals are found to be in good agreement
with the measurements. We find an enhancement of T for moderate doping
with nonmagnetic Sb and a suppression of T upon application of pressure,
both in agreement with experimental findings.Comment: Accepted for publication in PR
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