Effect of laser irradiation on activation energy, irreversibility field and upper critical magnetic field of bulk MgB2 superconductor

In this study, the role of laser irradiation on the upper critical field (H-c2), the irreversibility field (H-irr) and the activation energy (U-0) of bulk MgB2 superconductor was first time investigated with the aid of magnetoresistivity measurements conducted at different applied magnetic fields in a range of 0-15 kOe as a function of temperature from 25 to 40 K. For this aim, a disk shaped MgB2 superconductor was produced and cut into two pieces. One of the pieces was irradiated under high vacuum conditions by using an Nd:YVO4 laser. The obtained results showed an increase in the critical temperature (T-c) by about 1 K after irradiation. Also, the values of H-c2(0) were respectively found to be around 143 and 151 kOe while the values of H-irr(0) were about 122 and 130 kOe for the reference and the irradiated samples. Using the thermally activated flux flow model the dependence of U-0 on magnetic field was determined. The maximum U-0 values of 0.43 and 0.83 eV in zero magnetic field were respectively obtained for the reference and the irradiated samples. Also, the magnetic field dependence of the critical current density J(c)(B) values at different temperatures were slightly increased after the irradiation. These results point out that the superconducting properties of bulk MgB2 can be improved via laser irradiation.