Enhancement of superconducting parameters of MgB2 by low energy carbon ion implantation

The aim of work is to study the effects of carbon ion implantation on enhancement of superconducting properties of MgB2. Pure MgB2 bulk samples are irradiated by carbon ion beam of energy 40 keV (beam current 1 mu A) at different fluences. After irradiation, there is enhancement in superconducting properties viz., critical current density (J(c)), critical magnetic field (H-c2), comparing to pristine sample. Estimated with Ginzburg-Landau theory method at zero kelvin, the critical magnetic field H-c2(0) for irradiated sample shows an increase of 47 T than that of 38 T reported for pristine sample. There is also a four times increase in J(c) after implantation. Improvement in grain connectivity with ion fluence is found in surface morphological studies. Raman spectroscopic studies show a shift in resonance peak related with E-2g phonon modes after irradiation. This shifting is caused due to improvement in scattering and alteration of Fermi surface in implanted samples. These results are explained in correlation with the lattice disorder

Hydrostatic pressure-induced huge enhancement of critical current density and flux pinning in Fe1-xCoxSe0.5Te0.5 single crystals

We performed a systematic study of the hydrostatic pressure (HP) effect on the supercon-ducting transition temperature (T c ), critical current density (J c ), irreversibility field (H irr ), upper critical field (H c2 ), and flux pinning mechanism in un-doped and 3 at.% Co-doped FeSe 0.5 Te 0.5 crystals. We found that T c is increased from 11.5 to 17 K as HP increases from 0 to 1.2 GPa. Remarkably, the J c is significantly enhanced by a factor of 3 to 100 for low and high temperature and field, and the H irr line is shifted to higher fields by HP up to 1.2 GPa. Based on the collective pinning model, the δl pinning associated with charge-carrier mean free path fluctuation is responsible for the pinning mechanism of Fe 1-x Co x Se 0.5 Te 0.5 samples with or without pressure. A comprehensive vortex phase diagram in the mixed state is constructed and analysed for the 3 at.% Co-doped sample