G. Tewari | Weizmann Institute of Science (original) (raw)

Papers by G. Tewari

Journal of Magnetism and Magnetic Materials, 2015

The magnetic properties of the pnictide superconductors with the nominal composition of BaFe 2 (A... more The magnetic properties of the pnictide superconductors with the nominal composition of BaFe 2 (As 0.68 P 0.32 ) 2 and EuFe 2 (As 0.8 P 0.2 ) 2 were studied by 57 Fe Mössbauer spectroscopy. A superconducting transition at 30 K was detected and coexistence of magnetism and superconductivity at low temperatures was observed. The Mössbauer spectra show two different iron atoms surroundings, which are attributed to undoped AFe 2 As 2 and substituted AFe 2 (As 1−x P x ) 2 , with at least one phosphorus atoms in the tetragonal iron environment, (A = Ba or Eu).

Materials Chemistry and Physics, 2014

ABSTRACT Here we study thermoelectric and magnetic properties of CuCrSe2 samples sintered at vari... more ABSTRACT Here we study thermoelectric and magnetic properties of CuCrSe2 samples sintered at various temperatures. Structural analysis with XRD shows an order-disorder transition for Cr atoms when the sintering temperature is increased above 1273 K. Metal-like electrical resistivity and anomalously large Seebeck coefficient are found about room temperature. Analysis of electrical conductivity and Seebeck coefficient of the partially-disordered phase suggests hopping conduction of charge carriers. For both the ordered and disordered phases magnetic susceptibility follows Curie–Weiss temperature dependence at high temperatures above 150 K and shows an antiferromagnetic transition around 55 K. For the disordered phase, the effective magnetic moment is determined at 3.62 μB; this low value in comparison to the spin only value for Cr3+ of 3.89 μB indicates spin fluctuations in the paramagnetic state. The thermal conductivity in these phases is low and dominated by the lattice contribution. Values for the thermoelectric figure of merit (ZT) at room temperature are estimated to be 0.17 and 0.05 for the ordered and disordered phases, respectively.

Journal of Solid State Chemistry, 2013

We present a detail study of the electrical resistivity, thermoelectric power, magnetic susceptib... more We present a detail study of the electrical resistivity, thermoelectric power, magnetic susceptibility χ and the heat capacity C P in antiferromagnetic layered compounds CuCrS 2 and CuCrSe 2 at 2K-300K. CuCrS 2 showed sharp cusp in χ and a lambda-like peak in C P at T N = 40K as expected for a 3D-magnetic order, while more metallic CuCrSe 2 showed a rounded maximum in χ and the absence of sharp peak in C P around 55K, the C P at low temperature has T 2 -dependence in it which suggests the absence of the long range order and 2D spin-liquid like excitation in its magnetic phase. We explain the absence of the magnetic order in the selenide compound as resulting from the effective competition of the magnetic interactions from the distant neighbors; the indirect exchange among the intralayer Cr-atoms increases in more metallic selenide compound which competes with the direct antiferromagnetic interactions between the Cr-atoms of different layers which destroys the long range magnetic order. PACS number(s): 75.25.+z; 75.50.Ee; 72.15.Jf; 75.50.Pp

Journal of Physics: Condensed Matter, 2013

We present detailed electronic band-structure calculations for antiferromagnetic chromium compoun... more We present detailed electronic band-structure calculations for antiferromagnetic chromium compounds, CuCrX(2) (X = S, Se or Te), carried out using spin-polarized density functional theory within the generalized-gradient approximation (GGA). A narrow-band semiconductor-to-metal transition is observed upon replacement of S or Se by Te. The indirect bandgap is found at 0.58 eV and 0.157 eV for CuCrS(2) and CuCrSe(2), respectively. The results for our theoretical calculations are well in line with the electronic transport properties experimentally observed for CuCrS(2) and CuCrSe(2).

Journal of Magnetism and Magnetic Materials, 2014

ABSTRACT The behavior of the internal magnetic field in FeTe1−xSx was studied using M¨ossbauer sp... more ABSTRACT The behavior of the internal magnetic field in FeTe1−xSx was studied using M¨ossbauer spectroscopy in the temperature range from 6.8 K up to 300 K. Spectra of samples with x = 0.05, 0.10 and 0.20 were recorded and the obtained hyperfine parameters were compared with the superconductivity properties. A dependence of the internal field on the x value and the superconductivity transition temperature was found.

Hyperfine Interactions, 2013

Magnetic properties of the FeTe 0.8 S 0.2 superconductor were studied by Mössbauer spectroscopy. ... more Magnetic properties of the FeTe 0.8 S 0.2 superconductor were studied by Mössbauer spectroscopy. Low-velocity Mössbauer spectra that were recorded in the temperature range from 5.7 K up to 300 K show a paramagnetic doublet with a broadening at temperatures below 77 K. The broadening can be explained by the appearance of a distribution of hyperfine magnetic fields due to the magnetic ordering of a part of the sample. The magnetically ordered fraction starts to decrease at temperatures below 20 K indicating a possible competition with the onsetting superconductive state.

Hyperfine Interactions, 2014

We have studied the hyperfine interactions in samples belonging to the Fe-Se system. Several samp... more We have studied the hyperfine interactions in samples belonging to the Fe-Se system. Several samples with various concentrations of selenium were synthesized and investigated. The objective was to find synthesis conditions increasing the concentration of a secondary Fe-Se phase with a rather large quadrupole splitting of ∼1.7 mm/s. At T m ≈104 K this secondary phase undergoes a magnetic ordering.