Flux Pinning Mechanism in Single-Crystalline MgB

概要

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We investigate the flux pinning mechanism for single-crystalline MgB<inf>2</inf>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 MgB<inf>2</inf>thin films weak collective pinning is dominant at all temperatures, and the pinning mechanism shows a crossover from \delta T_{\text{c}}-pinning to \delta l-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.
2013-11-15