A. T. Satya

Superconductivity in Ru substituted polycrystalline BaFe 2-x Ru x As 2

The occurrence of bulk superconductivity at ~22 K is reported in polycrystalline samples of BaFe2-xRuxAs2 for nominal Ru content in the range of x=0.75 to 1.125. A systematic suppression of the spin density wave transition temperature (TSDW) precedes the appearance of superconductivity in the system. A phase diagram is proposed based on the measured TSDW and superconducting transition temperature (TC) variations as a function of Ru composition. Band structure calculations, indicate introduction of electron carriers in the system upon Ru substitutiom. The calculated magnetic moment on Fe shows a minimum at x=1.0, suggesting that the suppression of the magnetic moment is associated with the emergence of superconductivity. Results of low temperature and high field Mossbauer measurements are presented. These indicate weakening of magnetic interaction with Ru substitution

Pressure-induced metallization of BaMn2As2

The temperature and pressure dependent electrical resistivity rho(T,P) studies have been performed on BaMn2As2 single crystal in the 4.2 to 300 K range upto of 8.2 GPa to investigate the evolution of its ground state properties. The rho(T) shows a negative co-efficient of resistivity under pressure upto 3.2 GPa. The occurrence of an insulator to metal transition (MIT) in an external P ~4.5 GPa is indicated by a change in the temperature co-efficient in the rho(T) data at ~36 K . However complete metallization in entire temperature range is seen at a P~5.8 GPa. High pressure XRD studies carried out at room temperature also shows an anomaly in the pressure versus volume curve around P ~ 5 GPa, without a change in crystal structure, indicative of an electronic transition. Further, a clear precipitous drop in rho(T) at ~17 K is seen for P ~5.8 GPa which suggests the possibility of the system going over to a superconducting ground state.

Magnetic behavior of the metal organic framework [(CH3)2NH2]Co(HCOO)3

In this study we examine the phase transitions in single crystals of [(CH3)2NH2]Co(HCOO)3, using magnetization and specific heat measurements as a function of temperature and magnetic field. Magnetisation measurements indicate a transition at 15 K that is associated with an antiferromagnetic ordering. Isothermal magnetization versus magnetic field curves demonstrate the presence of a single-ion magnet phase, coexisting with antiferromagnetism. A peak in specific heat is seen at 15 K, corresponding to a magnetic transition and the enthalpy of the transition evaluated from the area under the specific heat peak which decreases with the application of a magnetic field of up to 8 T. This is suggestive of long range antiferromagnetic magnetic order, giving way to single-ion magnetic behavior under an external magnetic field. At high temperatures, the specific heat measurements show a peak at ∼155 K that is insensitive to the applied magnetic field. Raman scattering studies confirm the presence of a structural transition. The magnetisation in this temperature range, while exhibiting a paramagnetic behavior, shows a distinct jump and the paramagnetic susceptibility changes across the structural transition.

Tunable resistivity in magnetic glass phase of Gd1−xCaxBaCo2O5.5

We present magnetization and resistance measurements carried out on pristine and Ca-doped Gd(1-x)Ca(x)BaCo2O5.5 (x = 0.02) samples using the cooling and heating in unequal field (CHUF) protocol. The measurements reveal that the high temperature ferromagnetic phase is kinetically arrested at low temperature when the sample is cooled in a magnetic field. The volume fraction of this arrested phase increases upon Ca substitution and also by increasing the field in which the sample is cooled. Since the ferromagnetic phase is less resistive when compared to the low temperature antiferromagnetic phase, a tunable resistance is achieved in the sample by cooling in different magnetic fields. By cooling in magnetic fields of 9 T a reduction in resistivity by an order of magnitude is achieved. These results are consistent with the coexistence of the low temperature equilibrium antiferromagnetic phase with kinetically arrested high temperature ferromagnetic phase in the system.

Superconductivity in Ru-substituted polycrystalline BaFe2-xRuxAs2

The occurrence of bulk superconductivity at ~22 K is reported in polycrystalline samples of BaFe2-xRuxAs2 for nominal Ru content in the range of x=0.75 to 1.125. A systematic suppression of the spin density wave transition temperature (TSDW) precedes the appearance of superconductivity in the system. A phase diagram is proposed based on the measured TSDW and superconducting transition temperature (TC) variations as a function of Ru composition. Band structure calculations, indicate introduction of electron carriers in the system upon Ru substitutiom. The calculated magnetic moment on Fe shows a minimum at x=1.0, suggesting that the suppression of the magnetic moment is associated with the emergence of superconductivity. Results of low temperature and high field Mossbauer measurements are presented. These indicate weakening of magnetic interaction with Ru substitution

Superconductivity in Ru substituted BaFe2-xRuxAs2

The occurrence of bulk superconductivity at ~22 K is reported in polycrystalline samples of BaFe2-xRuxAs2 for nominal Ru content in the range of x=0.75 to 1.125. A systematic suppression of the spin density wave transition temperature (TSDW) precedes the appearance of superconductivity in the system. A phase diagram is proposed based on the measured TSDW and superconducting transition temperature (TC) variations as a function of Ru composition. Band structure calculations, indicate introduction of electron carriers in the system upon Ru substitutiom. The calculated magnetic moment on Fe shows a minimum at x=1.0, suggesting that the suppression of the magnetic moment is associated with the emergence of superconductivity. Results of low temperature and high field Mossbauer measurements are presented. These indicate weakening of magnetic interaction with Ru substitution

Evolution of ferromagnetic clustering in Pr0.5Ca0.5MnO3 and its effect on the critical temperature of YBa2Cu3O7 thin film

A thin film bilayer of Pr0.5Ca0.5MnO3 and YBa2Cu3O7 has been deposited on LaAlO3 substrate by pulsed laser deposition. XRD pattern confirms the formation of the bilayer. Current and magnetic field dependent resistance measurements have been carried out to study the proximity effect. These measurements have shown that the superconducting transition temperature (Tc) of YBa2Cu3O7 is suppressed to lower temperatures with a progressive increase in current. In addition, a hump like feature appears in resistivity near Tc with increase in applied current. The results are explained on the basis of the formation and growth of ferromagnetic clusters on account of charge order melting in Pr0.5Ca0.5MnO3 upon application of high current and magnetic field.

Upper critical field anisotropy in BaFe 2 − x Co x As 2 single crystals synthesized without flux

The upper critical field was measured up to 12 T for three BaFe

The pressure induced insulator to metal transition in FeSb2

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Effects of Dy sub lattice dilution on transport and magnetic properties in Dy1-xKxMnO3

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