Influence of the Superconducting State of YBa2Cu3O7-x Ceramics on the Nature of Collisions between Paramagnetic Dioxygen Molecules and the Ceramic Surface
Superconductor Science & Technology
, E-ISSN: 1361-6668
Boreskov Institute of Catalysis, prospekt akademika Lavrentieva, Novosibirsk 630090, Russia
Measuring the heating rate of well prepared superconducting ceramics YBa2 Cu3 O7-x in atmospheres of dinitrogen and dioxygen at 77.4-92 K, we have shown that the paramagnetic dioxygen molecules provide a less effective heat transfer to the YBa2 Cu3 O7-x than the diamagnetic dinitrogen molecules. It was suggested that the phenomenon results from the predominantly elastic collisions between the paramagnetic dioxygen molecules and the ceramic surface. The elasticity is induced by the superconducting state of the material possessing a high value of the lower critical field H c 1g = 1.04 × 104 A m-1 and with the mean size for the granules rms ~40 µm. If the value of applied field Ha >H c 1g the elastic collisions between dioxygen molecules and the superconductor surface are suppressed. For the superconductor with a low value of H c 1g = 1.4 × 103 A m-1 and rms ~10 µm there are no elastic collisions of dioxygen molecules with the superconducting surface. We propose that this phenomenon is associated with interaction between the paramagnetic moment of the dioxygen molecule and the magnetic flux `frozen' into the superconductor.