518 research outputs found
Structural and Magnetic Characterizations of Co2FeGa/SiO2 Nanoparticles Prepared via Chemical Route
We report the synthesis of Co2FeGa/SiO2 nanoparticles by sol-gel method and
characterization using x-ray diffraction (XRD), transmission electron
microscopy (TEM) and magnetic measurements. The Rietveld refinements of XRD
data with space group Fm-3m clearly show the formation of A2 disorder single
phase and the lattice constant is found to be 5.738 {\AA}. The
energy-dispersive x-ray spectroscopy (EDX) confirm the elemental composition
close the desired values. The value of coercivity is found to be around 283 Oe
and 126 Oe, measured at 10 K and 300 K, respectively. We observed the
saturation magnetization significantly lower than expected from Slater-Pauling
rule. This decrease in the magnetic moment might be due to the presence of
amorphous SiO2 during the synthesis process. A large content of small size SiO2
particles along with Co2FeGa nanoparticles are also found in TEM study.Comment: 4 pages, AIP conferenc
Growth and Characterization of Fe0.95Se0.6Te0.4 Single Crystal
In this paper we present the single crystal growth of Fe0.95Se0.6Te0.4 high
TC superconducting sample by the modified Bridgman technique. The x-ray
diffraction pattern shows the single crystal nature of the sample, as only
(00l) peaks are detectable. The stoichiometric composition has been verified by
energy dispersive x-ray analysis. The superconducting transition temperature at
14 K was confirmed through DC magnetization (ZFC-FC) and resistivity
measurements. By analyzing the isothermal M-H curves, we determined the value
of H_c1 (0) ~360 Oe by extrapolating the data. The temperature coefficient of
resistivity obtained using the power law fitting was found to be 0.6. The
obtained Raman spectra at room temperature can be interpreted with the
tetragonal crystal structure and space group P4/nmm.Comment: conference pape
Exploring the possibility of enhancing the figure-of-merit ( 2) of NaCoO: A combined experimental and theoretical study
Search of new thermoelectric (TE) materials with high
\textit{figure-of-merit} (ZT) is always inspired the researcher in TE field.
Here, we present a combined experimental and theoretical study of TE properties
of NaCoO compound in high-temperature region. The experimental
Seebeck coefficient (S) is found to vary from 64 to 118 V/K in the
temperature range K. The positive values of S are indicating the
dominating p-type behaviour of the compound. The observed value of thermal
conductivity () is 2.2 W/m-K at 300 K. In the temperature region
K, the value of increases up to 2.6 W/m-K and then
decreases slowly till 620 K with the corresponding value of 2.4 W/m-K.
We have also carried out the theoretical calculations and the best matching
between experimental and calculated values of transport properties are observed
in spin-polarized calculation within DFT+\textit{U} by chosen \textit{U} = 4
eV. The maximum calculated value of ZT is found to be 0.67 at 1200 K for
p-type conduction. Our computational study suggests that the possibility of
n-type behaviour of the compound which can lead to a large value of ZT at
higher temperature region. Electron doping of 5.110
cm is expected to give rise the high ZT value of 2.7 at 1200 K.
Using these temperature-dependent ZT values, we have calculated the maximum
possible values of efficiency () of thermoelectric generator (TEG) made
by p and n-type NaCoO. The present study suggests that one can
get the efficiency of a TE cell as high as 11 when the cold and hot
end temperature are fixed at 300 K and 1200 K, respectively. Such high values
of ZT and efficiency suggest that NaCoO can be used as a
potential candidate for high-temperature TE applications
Influence of Ni doping on the electronic structure of Ni_2MnGa
The modifications in the electronic structure of Ni_{2+x}Mn_{1-x}Ga by Ni
doping have been studied using full potential linearized augmented plane wave
method and ultra-violet photoemission spectroscopy. Ni 3d related electron
states appear due to formation of Ni clusters. We show the possibility of
changing the minority-spin DOS with Ni doping, while the majority-spin DOS
remains almost unchanged. The total magnetic moment decreases with excess Ni.
The total energy calculations corroborate the experimentally reported changes
in the Curie temperature and the martensitic transition temperature with x.Comment: 4 pages, 4 figures, accepted in Phys. Rev.
Evolution of complex magnetic phases and metal-insulator transition through Nb substitution in LaSrCoNbO
We report the evolution of structural, magnetic, transport, and electronic
properties of bulk polycrystalline LaSrCoNbO
( 0.025--0.25) samples. The Rietveld refinement of the x-ray diffraction
patterns with Rc space group reveals that the lattice parameters and
rhombohedral distortion monotonously increase with the Nb(4)
substitution (). The magnetic susceptibility exhibits a decrease in the
magnetic ordering temperature and net magnetization with , which manifests
that the Nb substitution dilutes the ferromagnetic (FM) double exchange
interaction and enhances the antiferromagnetic (AFM) super-exchange
interaction. Interestingly, for the 0.1 samples the FM order is completely
suppressed and the emergence of a glassy state is clearly evident. Moreover,
the decrease in the coercivity (H) and remanence (M) with
in the magnetic isotherms measured at 5~K further confirms the dominance of AFM
interactions and reduction of FM volume fraction for the 0.1 samples. More
interestingly, we observe resistivity minima for the 0.025 and 0.05
samples, which are analyzed using the quantum corrections in the conductivity,
and found that the weak localization effect dominates over the renormalized
electron-electron interactions in the 3D limit. Further, a semiconducting
resistivity behavior is obtained for 0.05, which follows the Arrhenius law
at high temperatures (160--320~K), and the 3D-variable range hopping
prevails in the low-temperature region (160~K). The core-level photoemission
spectra confirm the valence state of constituent elements and the absence of
Co is discernible.Comment: submitte
Dielectric properties and impedance spectroscopy of NASICON type NaZrSiPO
We report the temperature dependent dielectric properties and impedance
spectroscopy investigation of NaZrSiPO in the frequency
range of 20 Hz--2 MHz. The Rietveld refinement of x-ray diffraction pattern
confirms the monoclinic phase with C2/c space group. The {\it d.c.} resistivity
behavior shows its strong insulating nature at low temperatures, and follows
Arrhenius law of thermal conduction with an activation energy of 0.68 eV. The
decrease in electric permittivity () with frequency is explained
based on the space polarization mechanism and its increment with temperature by
thermal activation of charge carriers. The dielectric loss (D=tan) peak
follows the Arrhenius law of thermal activation with an energy of 0.25 eV. We
observe an enhancement in {\it a.c.} conductivity with frequency and
temperature due to the decrease in the activation energy, which results in
enhancing the conduction between defect states. Further, we observe an abrupt
increase in the {\it a.c.} conductivity at high frequencies, which is explained
using the universal Jonschers power law. The analysis of {\it a.c.}
conductivity shows two types of conduction mechanisms namely correlated barrier
hopping and non-overlapping small polaron tunnelling in the measured
temperature range. The imaginary part of the electric modulus confirms the
non-Debye type relaxation in the sample. The shifting of the relaxation peak
towards higher frequency side with an increase in temperature ensures its
thermally activated nature. The scaling behavior of the electric modulus shows
similar type of relaxation over the measured temperature range. The combined
analysis of electric modulus and impedance with frequency shows the short-range
mobility of charge carriers.Comment: submitte
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