Magnetic depth profile of La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ / YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ trilayers

Recent experiments showed magnetoresistance in excess of 1000\% in epitaxial tri- layers containing highly spin polarized La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ (LCMO) manganite and high Tc superconducting YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ [1]. This large magnetoresistance originates from spin imbalance due to the injection of spin polarized carriers. In a series of trilayers, with varying LCMO layer thickness, polarized neutron reflectometry has determined the detailed magnetization depth profile. For trilayers exhibiting a strong magnetoresistance, differences in the magnetization profiles of the two LCMO layers is observed, providing a mechanism for antiferromagnetic alignment during the magnetization reversal process. Obtained details of the magnetization at the interfaces lead to a better understanding of these variations. [1] V. Pe\~{n}a {\it et al.}, Phys. Rev. Lett {\bf 94} (2005) 057002.