The suppression of superconductivity in Mn substituted MgCNi3_{3}

We report the effect of doping Mn in the isostructural MgCNi$_{3-x}$Mn$_{x}$ (x = 0-0.05) compounds. Magnetic susceptibility, resistivity, magneto-resistance, and specific heat studies show evidence of localized moments and Kondo effect in samples with x$\neq$0. The rapid suppression of superconductivity ($\sim$ -21K/at.% Mn) in these compounds is a consequence of pair breaking effects due to moment formation on Mn.Comment: 9 figures, Accepted for publication in Physical Review B, Added reference

Voltage bias induced modification of all oxide Pr0.5Ca0.5MnO3/SrTi0.95Nb.05O3 junctions

In this paper we report what happens to a pristine oxide junction Pr0.5Ca0.5MnO3/SrTi0.95Nb.05O3 (PCMO/Nb:STO), when it is subjected to cycling of voltage bias of moderate value ({\pm}4V). It is found that the initial cycling leads to formation of a permanent state of lower resistance where the lower resistance arises predominantly due to development of a shunt across the device film (PCMO). On successive voltage cycling with increasing magnitude, this state transforms into states of successive lower resistance that can be transformed back to the initial stable state on cycling to below a certain bias. A simple model based on p-n junction with shunt has been used to obtain information on the change of the junction on voltage cycling. It has been shown that the observation can be explained if the voltage cycling leads to lowering of barrier at the interface and also reduction in series resistance. It is suggested that this lowering can be related to the migration of oxygen ions and vacancies at the junction region. Cross-sectional imaging of the junction shows formation of permanent filamentary bridges across the thickness of the PCMO after the pristine p-n junction is first taken through a voltage cycle, which would explain appearance of a finite shunt across the p-n junction.Comment: 12 pages,7figure