Superconducting magnetic levitation force measurements on large field cooled cylindrical MgB₂ bulks with different diameters and thicknesses are reported. For these experiments, a special set-up permitting one to measure forces up to 500 N was used. In contradiction to previous measurements, the obtained force hysteresis cycles could not be reproduced with the analytical mean field model proposed by Bernstein et al (2017 Supercond. Sci. Technol. 30 065007). The failure of the model has been attributed to surface barriers effects which were not taken into account in the model. This last one was accordingly modified in order that the measured force cycles could be reproduced. Contrary to most other models describing surface barriers effects, the modified model suggests that above a threshold field anti-vortices and not vortices enter the superconductor. This behaviour is related to the storage by the superconductor of the mechanical work done by the operator. In addition, it has turned out that the threshold field is a decreasing function of the critical surface current density of the samples. As a consequence, the surface barriers effects occur only if this quantity and the critical current density are large enough. Otherwise, the internal magnetic field of the superconductor could be computed and was seen to be a decreasing function of the thickness of the superconductors.

中文翻译：

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表面势垒对圆柱形超导体磁悬浮的可能影响

报告了对不同直径和厚度的大场冷却圆柱形 MgB ₂块体的超导磁悬浮力测量。在这些实验中，使用了一种特殊的装置，可以测量高达 500 N 的力。与之前的测量相矛盾的是，所获得的力滞后周期无法用伯恩斯坦提出的分析平均场模型重现等人(2017年超条件。科学。技术。 30065007）。该模型的失败归因于模型中未考虑的表面障碍效应。最后一个进行了相应的修改，以便可以重现测量的力循环。与描述表面势垒效应的大多数其他模型相反，修改后的模型表明，在阈值以上，场反涡流而不是涡流进入超导体。这种行为与超导体存储操作者所做的机械功有关。此外，事实证明阈值场是样品临界表面电流密度的递减函数。因此，只有当这个量和临界电流密度足够大时，才会出现表面势垒效应。否则，可以计算超导体的内部磁场，并将其视为超导体厚度的递减函数。