11 research outputs found
Effect of Hetrovalent substitution at Mn site on the Magnetic and Transport Properties of LaSrMnO
Magnetic and transport properties of Ti substituted
LaSrMnO are drastically affected with a change in
preparation conditions. Low temperature infra-red absorption measurements
reveal that this is perhaps due to inhomogeniety in substitution of Ti
on Mn sites. It is found that, in the high temperature annealed samples, the
substitution of Ti supresses the double exchange interaction due to the
formation of Mn-O-Ti chains. While in the low temperature
annealed case substitution of Ti causes formation of isolated ferromagnetic
clusters linked to each other by a variable range hopping polaron.Comment: 11 pages, 8 figures, accepted in J. Magn. Magn. Magn. Mate
Structure, Transport and Magnetic properties in LaSrCoRuO
The perovskite solid solutions of the type
LaSrCoRuO with 0.25 x
0.75 have been investigated for their structural, magnetic and transport
properties. All the compounds crystallize in double perovskite structure. The
magnetization measurements indicate a complex magnetic ground state with strong
competition between ferromagnetic and antiferromagnetic interactions.
Resistivity of the compounds is in confirmation with hopping conduction
behaviour though differences are noted especially for = 0.4 and 0.6. Most
importantly, low field (50Oe) magnetization measurements display negative
magnetization during the zero field cooled cycle. X-ray photoelectron
spectroscopy measurements indicate presence of Co/Co and
Ru/Ru redox couples in all compositions except = 0.5.
Presence of magnetic ions like Ru and Co gives rise to additional
ferromagnetic (Ru-rich) and antiferromagnetic sublattices and also explains the
observed negative magnetization.Comment: Accepted for publication in J. Magn. Magn. Mate
Low Temperature Neutron Diffraction Study of MnTe
Investigation of transport and magnetic properties of MnTe at low
temperatures sInvestigation of transport and magnetic properties of MnTe at low
temperatures showed anomalies like negative coefficient of resistance below
100K and a sharp rise in susceptibility at around 83K similar to a
ferromagnetic transition. Low temperature powder neutron diffraction
experiments were therefore carried out to understand the underlying phenomena
responsible for such anomalous behavior. Our study indicates that the rise in
susceptibility at low temperatures is due to strengthening of ferromagnetic
interaction within the plane over the inter plane antiferromagnetic
interactions.Comment: Appearing in J. Magn. Magn. Mate
Infra-red Spectroscopic Studies of GdBaCo2O5.5
This paper reports infrared spectroscopic studies on GdBaCoO
layered perovskite which exhibits successive magnetic transitions from
paramagnetic to ferromagnetic to antiferromagnetic states as well as high
temperature metal to insulator transition and a change in charge transport
mechanism at low temperature. Infrared absorption spectra recorded at various
temperatures in the range 80 K to 350 K reveal changes in the positions of Co-O
stretching and bending frequencies which provide an explanation to the magnetic
and transport behaviour of this compound.Comment: 5 figure
Infrared absorption study of charge ordered
Infrared absorption study has been carried out on a series of half doped
manganites, , with
varying magnetic ground state. The charge ordering transition observed in
samples with {\normalsize is accompanied by a mode at
in addition to the stretching mode at and bending
mode at . Phonon hardening is found to occur below the CE - type
antiferromagnetic ordering temperature. The value of the insulating gap
decreases on doping with Sr from to }Comment: 14 pages, 5 figures, To appear in Physica
Heterogeneous magnetism and kinetic arrest in antiperovskite Mn3 xNixGaC compounds with Ni2MnGa Heusler insertions
Role of manganese in red long-lasting phosphorescence of manganese-doped diopside for in vivo imaging
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Tailoring a Pt–Ru catalyst for enhanced methanol electro-oxidation
A carbon-supported (1:1) Pt–Ru (Pt–Ru/C) alloy catalyst has been prepared in-house by the sulfito-complex route, and has been tailored to
achieve enhanced activity towards methanol electro-oxidation by annealing it at varying temperatures in air. The catalyst samples annealed
between 250 and 300 ◦C in air for 30 min exhibit superior catalytic activity towards methanol electro-oxidation in a solid-polymer-electrolyte
direct methanol fuel cell (SPE-DMFCs) operating at 90 ◦C. Both the as-prepared and annealed Pt–Ru/C catalysts have been characterized
by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), extended X-ray
absorption fine structure (EXAFS), and cyclic voltammetry. It is conjectured that while annealing the Pt–Ru/C catalysts, both Pt Pt and
Pt Ru bonds increase whereas the Pt O bond shrinks. This is accompanied with a positive variation in Ru/Pt metal ratio suggesting the
diffusion of Ru metal from the bulk catalyst to surface with an increase in oxidic ruthenium content. Such a treatment appears seminal for
enhancing the electrochemical activity of Pt–Ru catalysts towards methanol oxidation
Ultra-Low Temperature CO Oxidation Activity of Octahedral Site Cobalt Species in Co3O4 Based Catalysts: Unravelling the Origin of Unique Catalytic Property
Co3O4 with spinel structure shows CO oxidation activity at very low temperature under dry conditions. This study aims at finding the origin of the unique catalytic activity of Co species in Co3O4 based oxides. Although, octahedral site Co3+ species have been reported to be active in Co3O4 based catalysts, there is no solid explanation as to why Co is so special as compared with other metals like Fe having similar redox states. In this study, mainly, three model spinel catalysts including MnCo2O4, MnFe2O4, and CoCr2O4 have been chosen. A detailed analysis of bulk and crystal surface structure, surface properties of the catalysts, and redox properties of the active metals has been performed to understand the unusual catalytic activity. Low-temperature CO oxidation activity decreases in the following order: MnCo2O4 ≫ MnFe2O4 > CoCr2O4. It indicates that the Co2+ species in a tetrahedral site (in CoCr2O4) remains inactive for low-temperature catalytic activity, while Co3+ in an octahedral site (in MnCo2O4) is active in Co3O4 based catalysts. This result is corroborated with CoFe2O4 which shows a higher activity than CoCr2O4, as it has partial occupation of the octahedral site. Fe, being a weak redox metal, does not show low-temperature activity, although crystallite facets of MnCo2O4 and MnFe2O4 catalysts are predominantly exposed in the (100) and (110) lattice planes, which contain quite similar concentrations of Co3+ and Fe3+ species in both. The intensity of the redox peak for CO oxidation involving a Co3+/Co2+ couple in MnCo2O4 indicates a highly favorable reaction, while a nonresponsive behavior of Co species is observed in CoCr2O4. As expected, MnFe2O4 is proven to be weak, giving a much lower intensity of electrochemical CO oxidation. Both CO- and H2-TPR indicate a much higher reducibility of Co species in MnCo2O4 as compared with Co species in CoCr2O4 or Fe in MnFe2O4