Interpretation of large room-temperature diamagnetism at low magnetic fields in films of oxidized atactic polypropylene in terms of superconducting current loops

摘要

A simple model is used to analyze published results on large room-temperature diamagnetism for two films of oxidized atactic polypropylene (OAPP) at low magnetic fields. The model involves induced currents expected in circular closed loops of superconductors in fields below the lower critical field H{sub}(c1) at which flux penetration would first occur if a metamagnetic transition did not intervene as in OAPP, and the assumption that resistance would be restored at H{sub}(c1) (negligible pinning). Fits to the data for the more strongly magnetic sample with the model, allowing two different types of loops with different loop radii b{sub}1 and b{sub}2, but with the same cross-section a of loop material yield H{sub}(c1)≈5260 Oe, and fits to the data for the less strongly magnetic sample with two loop sizes and with the same value of H{sub}(c1), combined with the knowledge that the minimum number of closed loops of any type is 1, requires that the radius a of the cross-section of the material should be less than about 0.8 μm, in fair agreement with the maximum radius of 1 μm obtained previously from other data.