The origin of paramagnetic magnetization in field-cooled YBa2Cu3O7 films

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Temperature dependences of the magnetic moment have been measured in YBa₂Cu₃O₇₋δ thin films over a wide magnetic field range (5 <= H <= 10⁴ Oe). In these films a paramagnetic signal known as the paramagnetic Meissner effect has been observed. The experimental data in the films, which have strong pinning and high critical current densities (Jc 2 × 10⁶ A/cm² at 77 K), are quantitatively shown to be highly consistent with the theoretical model proposed by Koshelev and Larkin [Phys. Rev. B 52, 13559 (1995)]. This finding indicates that the origin of the paramagnetic effect is ultimately associated with nucleation and inhomogeneous spatial redistribution of magnetic vortices in a sample which is cooled down in a magnetic field. It is also shown that the distribution of vortices is extremely sensitive to the interplay of film properties and the real experimental conditions of the measurements.