Changes in Nd:YVO4 laser irradiated MgB2 bulk superconductors

Abstract

MgB2 bulk superconductors were fabricated by an in-situ solid state reaction method. The surface of the MgB2 samples thus obtained was irradiated, under high vacuum, in dot-shape geometric patterns by using a Nd:YVO4 diode-pumped laser, to investigate the effect of laser irradiation on their structure, microstructure and magnetic properties. Structural and microstructure changes were analysed by using X-ray diffraction (XRD), confocal and scanning electron microscopy (SEM). The magnetic properties (M-H curves) of the samples were determined using a magnetic properties measurement system (MPMS). The magnetic field dependence of the critical current density, Jc was calculated from M(H) loops by using Bean’s critical model at 5 K and 20 K. The results indicate that the Jc value enhanced at a certain ratio in the irradiated superconductors compared to the un-irradiated ones. To confirm that the improvement in Jc of the irradiated MgB2 is due to an improved flux-pinning behaviour, the variation of Fp/Fp,max with magnetic field was calculated at 5 K. It was found that the pinning force curves of the irradiated samples shift toward the high field side indicating an improvement in the flux pinning with respect to the un-irradiated samples. These results show that the patterns are effective to improve the flux pinning in MgB2 bulk superconductors.