M. Kanagaraj

Pressure induced structural transition and enhancement of superconductivity in Co doped CeFeAsO

The superconducting CeFe1−xCoxAsO (Co=0.1) oxyarsenide with a transition temperature (Tc) 11.4 K has been investigated by in situ high pressure synchrotron x-ray diffraction, magnetization, and resistivity measurements. The experiments performed at 10 K up to 6 GPa and at room temperature (RT) up to 55 GPa indicate large anisotropic lattice compression. A pressure induced structural change to a collapsed tetragonal structure is observed above 10 GPa at RT. We report here the enhancement of Tc from 11.4 to 12.3 K with a small increase in pressure up to 0.4 GPa and is first observed in an electron doped Ce-1111 system.

Correlation between superconductivity and structural properties under high pressure of iron pnictide superconductor Ce0.6Y0.4FeAsO0.8F0.2

We report here the pressure dependence of the electrical resistivity and magnetic susceptibility of polycrystalline Ce0.6Y0.4FeAsO0.8F0.2 superconductor in the temperature range 4 K to 300 K up to 8 GPa. In-situ high pressure-low temperature x-ray diffraction was performed at 8 K up to 32 GPa using synchrotron x-rays with helium pressure medium. The results show that the applied pressure slightly increases the Tc up to 1 GPa and then it decreases on further pressure increase. The reduction of superconducting transition temperature occurs with a transition to a collapsed tetragonal phase and may be associated with a possible valence change of Ce.

Enhanced upper critical field, critical current density, and thermal activation energy in new ytterbium doped CeFeAsO0.9F0.1 superconductor

In this report, we have investigated the essential physical properties of Ce0.7Yb0.3FeAsO0.9F0.1 superconductor such as field dependent critical current density (Jc), thermal activation energy (U0), and upper critical field (Hc2). From the isothermal magnetization curves and size of the superconducting grains, the critical current density Jc of 2.3 × 106 A/cm2 at 2 K, 0.5 T was estimated using the Beans model for this Yb doped superconductor. A gradual decrease of Jc and absence of peak effect were found on increasing magnetic field up to 5 T. Thermal activation energy (U0/kB = ∼2500 K) calculated from Arrhenius plots at low magnetic field (0.5 T) indicates a strong flux pinning potential might be co-existing with applied magnetic field. Our results suggest that this new Yb doped superconductor is a possible practical high temperature superconductor under certain magnetic field and temperature.