Flux pinning properties of MgB2 thin films on Al tape substrates deposited by electron beam evaporation

Flux pinning properties have been investigated in two kinds of MgB2 thin films deposited on Al tapes by electron beam evaporation: One is a stoichiometric composition and the other is a slightly B-rich composition. The values of critical current density J(c) in both MgB2 thin films on Al tape substrates at 10 K in the magnetic field parallel to the c-axis are higher than those in MgB2 thin films on Si and Al2O3 substrates prepared by the same method. Both the MgB2 thin films on Al tapes show the large peaks for a magnetic field. B//c in the field-angular dependence of J(c). This result indicates that the MgB2 thin films have the c-axis correlated pinning centers. Scaling analysis in the reduced macroscopic pinning force density versus the reduced magnetic field at 20 K implies that a main pinning center in both the MgB2 thin films is grain boundaries. In addition, it was suggested that a nonstoichiometric MgB2 thin film has additional pinning centers which act effectively in a high magnetic field. (C) 2011 Published by Elsevier B.V.