Flux Pinning Mechanism in Single-Crystalline MgB2Thin Films

Abstract

We investigate the flux pinning mechanism for single-crystalline MgB2 thin films showing a peculiar flux pinning force behavior. The vortex–vortex distance is considered in this study through an analysis of the critical current density (\(J_{\text{c}}\)) and the flux pinning force density (\(F_{\text{p}}\)) over a wide range of temperatures from 5 to 35 K. Two unusual kinds of peaks, a near zero-field peak like a hump and another peak with a broad shape, are observed in the field dependences of the \(F_{\text{p}}\). The second peak with a broad shape begins to be depressed at temperatures above 25 K while the first sharp peak is only detected at temperatures above 30 K. In the single-crystalline MgB2 thin films weak collective pinning is dominant at all temperatures, and the pinning mechanism shows a crossover from δTc-pinning to δl-pinning with increasing magnetic field. We describe these unique features by considering the relation between the inter-vortex distances and the vortex–vortex interaction energy.