Abstract: The present invention relates to a core composite film for magnetic/nonmagnetic/magnetic multilayer thin film comprising a free magnetic layer, a spacer layer and a pinned magnetic layer. As the core composite film, it may be only the spacer layer is an LB film; and the spacer layer is an organic LB film consisting of materials with insulative, conductive or semiconductive character. As the core composite film, it may also be said free magnetic layer, spacer layer and pinned magnetic layer are all LB films; wherein the pinned magnetic layer and the free magnetic layer are organic films made of magnetic materials. The core composite film can be applied to a magnetic spin valve sensor, which can compose a magnetic induction unit of a magnetic spin valve sensor; and it can also be applied to a magnetic random access memory as a memory cell.