Origin of paramagnetic magnetization in field-cooledYBa2Cu3O7−δfilms

Abstract

Temperature dependences of the magnetic moment have been measured in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ thin films over a wide magnetic-field range $(5<~H<~{10}^{4}\mathrm{Oe}).$ 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 ${(J}_{c}\ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}{10}^{6}{\mathrm{A}/\mathrm{c}\mathrm{m}}^{2}$ at 77 K), are shown to be highly consistent with the theoretical model proposed by Koshelev and Larkin [Phys. Rev. B 52, 13 559 (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.