Browsing by Subject "Surface barriers"

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Open Access
Bean-Livingston surface barriers for flux penetration in Bi 2Sr 2CaCu 2O 8+δ single crystals near the transition temperature
(2011) Mihalache V.; Dede, M.; Oral, A.; Miu L.
The first field for magnetic flux penetration H p in Bi 2Sr 2CaCu 2O 8+δ (Bi-2212) single crystals near the critical temperature T c was investigated from the local magnetic hysteresis loops registered for different magnetic field H sweeping rates by using a scanning Hall probe microscope (SHPM) with ∼1 μm effective spatial resolution. Evidences for a significant role of the surface barrier were obtained: the asymmetric shape of the magnetization loops and an anomalous change in the slope of H p(T) close to T c. © 2011 Elsevier B.V. All rights reserved.
Open Access
Vortex imaging with varying temperature revealed by SHPM on Bi2Sr2CaCu2O8+y
(Elsevier B.V., 2008) Mihalache, V.; Dede, M.; Oral, A.; Sandu, V.
Scanning Hall probe microscopy with an effective spatial resolution of ∼1 μm has been used to investigate the vortex structures in superconducting Bi2Sr2CaCu2O8+δ single crystals in the temperature range 77.3-81.3 K and zero applied field (in the presence of the earth field). The vortex images were obtained in real time mode as the temperature increased slowly for 3.36 h. At 77.3 K, the vortices were arranged in a chain structure. With the increase of the temperature, two jumps in the vortex array occur at 77.3 K, immediately when the temperature starts to rise, and at 79.2 K with a good stability between jumps. The second jump is accompanied by the jump in the average magnetic induction when bundles of 4-5 additional vortices enter the scanning area and the vortex array get disordered. These directly visualized transitions in the vortex lattice are consistent with a vortex creep over the surface barriers at high temperatures. A short movie is presented. ,