2,810 research outputs found
Electronic structure of Fe and magnetism in the double perovskites CaFeReO and BaFeReO
The Fe electronic structure and magnetism in (i) monoclinic CaFeReO
with a metal-insulator transition at K and (ii) quasi-cubic
half-metallic BaFeReO ceramic double perovskites are probed by soft
x-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD).
These materials show distinct Fe XAS and XMCD spectra, which are
primarily associated with their different average Fe oxidation states (close to
Fe for CaFeReO and intermediate between Fe and Fe
for BaFeReO) despite being related by an isoelectronic
(Ca/Ba) substitution. For CaFeReO, the powder-averaged Fe
spin moment along the field direction ( T), as probed by the XMCD
experiment, is strongly reduced in comparison with the spontaneous Fe moment
previously obtained by neutron diffraction, consistent with a scenario where
the magnetic moments are constrained to remain within an easy plane. For
T, the unsaturated XMCD signal is reduced below consistent with a
magnetic transition to an easy-axis state that further reduces the
powder-averaged magnetization in the field direction. For BaFeReO, the
field-aligned Fe spins are larger than for CaFeReO ( T) and the
temperature dependence of the Fe magnetic moment is consistent with the
magnetic ordering transition at K. Our results illustrate the
dramatic influence of the specific spin-orbital configuration of Re
electrons on the Fe local magnetism of these Fe/Re double perovskites.Comment: 7 pages, 3 figure
On the Balance of Intercalation and Conversion Reactions in Battery Cathodes
We present a thermodynamic analysis of the driving forces for intercalation
and conversion reactions in battery cathodes across a range of possible working
ion, transition metal, and anion chemistries. Using this body of results, we
analyze the importance of polymorph selection as well as chemical composition
on the ability of a host cathode to support intercalation reactions. We find
that the accessibility of high energy charged polymorphs in oxides generally
leads to larger intercalation voltages favoring intercalation reactions,
whereas sulfides and selenides tend to favor conversion reactions. Furthermore,
we observe that Cr-containing cathodes favor intercalation more strongly than
those with other transition metals. Finally, we conclude that two-electron
reduction of transition metals (as is possible with the intercalation of a
ion) will favor conversion reactions in the compositions we studied
The Yoneda algebra of a graded Ore extension
Let A be a connected-graded algebra with trivial module k, and let B be a
graded Ore extension of A. We relate the structure of the Yoneda algebra E(A)
:= Ext_A(k,k) to E(B). Cassidy and Shelton have shown that when A satisfies
their K_2 property, B will also be K_2. We prove the converse of this result.Comment: 9 page
Angular Resolution of an EAS Array for Gamma Ray Astronomy at Energies Greater Than 5 x 10 (13) Ev
A 24 detector extensive air shower array is being operated at Ootacamund (2300 m altitude, 11.4 deg N latitude) in southern India for a study of arrival directions of showers of energies greater than 5 x 10 to the 13th power eV. Various configurations of the array of detectors have been used to estimate the accuracy in determination of arrival angle of showers with such an array. These studies show that it is possible to achieve an angular resolution of better than 2 deg with the Ooty array for search for point sources of Cosmic gamma rays at energies above 5 x 10 to the 13th power eV
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