C. S. Yadav

Magnetic phase diagram of Fe1.1Te1-xSex: A comparative study with the stoichiometric superconducting FeTe1-xSex system

We report a comparative study of the series Fe1.1Te1−xSex and the stoichiometric FeTe1−xSex to bring out the difference in their magnetic, superconducting and electronic properties. The Fe1.1Te1−xSex series is found to be magnetic and its microscopic properties are elucidated through Mossbauer spectroscopy. The magnetic phase diagram of Fe1.1Te1−xSex is traced out and it shows the emergence of spin-glass state when the antiferromagnetic state is destabilized by the Se substitution. The isomer shift and quadrupolar splitting obtained from the Mossbauer spectroscopy clearly brings out the electronic differences in these two series.

The flux pinning force and vortex phase diagram of single crystal FeTe0.60Se0.40

Abstract The flux pinning force density ( F p ) of the single crystalline FeTe 0.60 Se 0.40 superconductor has been calculated from magnetization measurements. The normalized F p versus h ( = H / H i r r ) curves are scaled using the Dew–Hughes’s formula f ( h ) ∼ h p ( 1 − h ) q to underline the pinning mechanism in the compound. The obtained values of pinning parameters ‘ p ’ and ‘ q ’ indicate point core pinning of the normal centers along with the presence of the surface pinning. The vortex phase diagram has also been drawn for the first time for FeTe 0.60 Se 0.40 , which has very high values of critical current density J c ∼ 1 × 10 5 A/cm 2 at T = 2 K and, the upper critical field H c 2 ( 0 ) ∼ 65 T , with a reasonably high transition temperature T c = 14.5 K .

Evolution of magnetic and dielectric properties in Sr-substituted high-temperature multiferroic YBaCuFeO5

We report the evolution of structural, magnetic and dielectric properties due to partial substitution of Ba by Sr in the high temperature multiferroic YBaCuFeO5. This compound exhibits ferroelectric and antiferromagnetic transitions around 200 K and these two phenomena are presumed to be coupled with each other. Our studies on magnetic and dielectric properties of the YBa1-xSrxCuFeO5 (x = 0.0, 0.25 and 0.5) show that substitution of Sr shifts magnetic transition towards higher temperature whereas dielectric transition to lower temperature. These results points to the fact that magnetic and dielectric transitions get decoupled as a result of chemical pressure in form of Sr substitution. The nature of magnetodielectric coupling changes across the series with the presence of higher order coupling terms. Additionally in these compounds glassy dynamics of electric dipoles is observed at low temperatures.

Peculiar magnetism of transition metal cluster compounds

We discuss a class of solids which have in their structure fairly separated tetrahederal clusters of transition metals: vanadium and molybednum. With decreasing temperature these compounds undergo a structural transition from cubic to rhombohederal phase at a temperature Ts, followed by a transition to a ferromagnetic phase at a lower temperarure Tc. Magnetic measurements indicate the presence of moments of spin half per cluster. Between Tc and Ts susceptibility shows large departures from Curie-Weiss behavior and specific heat has an unusually large non-phononic contribution. We present a model in which each cluster acts as a unit associated with a magnetic moment of spin half and a structural degree of freedom related to distortions of the tetrahedron. Our model accounts for all the observed features including effects due to external pressure and magnetic field.

Investigation of thermodynamic properties of multiferroic YBaCuFeO5

We present the results of magnetization and heat capacity measurements on multiferroic YBaCuFeO5 compound. The compound exhibits commensurate to incommensurate antiferromagnetic transition below TN ∼ 220 K. Heat capacity data were analyzed with Debye and Einstein models in the commensurate antiferromagnetic regime. The optical phonon modes give the predominant contribution to the heat capacity besides the acoustic phonon modes. The fit to experimental data gives the Debye temperature and Einstein temperature values as 234 K and 460 K respectively.We present the results of magnetization and heat capacity measurements on multiferroic YBaCuFeO5 compound. The compound exhibits commensurate to incommensurate antiferromagnetic transition below TN ∼ 220 K. Heat capacity data were analyzed with Debye and Einstein models in the commensurate antiferromagnetic regime. The optical phonon modes give the predominant contribution to the heat capacity besides the acoustic phonon modes. The fit to experimental data gives the Debye temperature and Einstein temperature values as 234 K and 460 K respectively.

Electronic transport properties of intermediately coupled superconductors: PdTe2 and Cu0.04PdTe2

We have investigated the electrical resistivity, Seebeck coefficient and thermal conductivity of PdTe2 and 4% Cu intercalated PdTe2 compounds. Electrical resistivity for the compounds shows Bloch-Gruneisen type linear temperature (T) dependence for 100 K < T < 480 K, and Fermi liquid behavior (~ T^2) below 50 K. Seebeck coefficient data exhibit strong competition between Normal (N) and Umklapp (U) scattering processes at low T. Though our results indicate the transfer of charge carriers to PdTe2 upon Cu intercalation, it is difficult to discern any change in the Fermi surface of the compound by Nordheim-Gorter plots. The estimated Fermi energies of the compounds are quite comparable to good metals Cu, Ag and Au. The low T, thermal conductivity (k) of the compounds is strongly dominated by the electronic contribution, and exhibits a rare linear T dependence below 10 K. However, high T, k(T) shows usual 1/T dependence, dominated by U scattering process. The electron phonon coupling parameters, estimated from the low T, specific heat data and first principle electronic structure calculations suggest that PdTe2 and Cu0.04PdTe2 are intermediately coupled superconductors.

Crystal structure and magnetism of layered perovskites compound EuBaCuFeO5

Layered perovskite compounds have interesting multiferroic properties.YBaCuFeO5 is one of the layered perovskite compounds which have magnetic and dielectric transition above 200 K. The multiferroic properties can be tuned with the replacement of Y with some other rare earth ions. In this manuscript, structural and magnetic properties of layered perovskite compound EuBaCuFeO5 have been investigated. This compound crystallizes in the tetragonal structure with P4mm space group and is iso-structural with YBaCuFeO5. The magnetic transition has been found to shift to 120 K as compared to YBaCuFeO5 which has the transition at 200 K. This shift in the magnetic transition has been ascribed to the decrease in the chemical pressure that relaxes the magnetic moments.Layered perovskite compounds have interesting multiferroic properties.YBaCuFeO5 is one of the layered perovskite compounds which have magnetic and dielectric transition above 200 K. The multiferroic properties can be tuned with the replacement of Y with some other rare earth ions. In this manuscript, structural and magnetic properties of layered perovskite compound EuBaCuFeO5 have been investigated. This compound crystallizes in the tetragonal structure with P4mm space group and is iso-structural with YBaCuFeO5. The magnetic transition has been found to shift to 120 K as compared to YBaCuFeO5 which has the transition at 200 K. This shift in the magnetic transition has been ascribed to the decrease in the chemical pressure that relaxes the magnetic moments.

Synthesis of Cubic Indium Oxide Thin Film by Microwave Irradiation

The indium metal thin films were deposited at room temperature by dc magnetron sputtering on glass substrate. This indium thin film is post-treated with microwave irradiation at ambient atmosphere to convert it into the In2O3 thin film. Indium oxide (In2O3) thin film was successfully synthesized on glass substrate by using microwave irradiation. This method has advantages over the conventional heating method because it takes lesser treatment time, and the quality of film is better. The effect of microwave irradiation for different time was studied by XRD and UV–VIS spectroscopy. X-ray diffraction result shows the presence of cubic phases in synthesized In2O3 thin film without any significant impurity. Optical spectroscopy measurements show a large optical transparency, greater than 60 %. This In2O3 thin film is highly suitable for the transparent conducting oxide, solar cell and gas sensor applications.