Interaction of vortices with different types of pinning centers in MgB ₂ superconducting films

This contribution reports on the magnetic response of two MgB₂ films with 600 nm of thickness. These films were grown using the hybrid physical chemical vapor deposition (HPCVD) method under different temperatures. One of the films, grown at 580 °C, has a micro structure with columnar grains, a rough surface and small grain size. The other, grown at 650 °C, has a smooth surface and larger grains. A double transition is present in the columnar sample. The lower transition temperature is due to currents tunneling through the intergrain material and the higher one is associated with the transition of the grains to the normal state. Magnetic phase diagrams in tilted geometries, with the applied fields (AC and DC) forming angles in the range (0°, 90°) with the plane of the film, were determined to verify the influence of the perpendicular component of the AC field on pinned vortices. Hysteresis loops of magnetization versus applied field were also measured for both samples. The columnar sample exhibits jumps in the decreasing field branch of the magnetization, indicating that vortices pinned by the columnar microstructures leave the sample in bundles.