Tuning unexpected room temperature ferromagnetism in heteroepitaxial PbTiO3 thin films fabricated by hydrothermal epitaxy: crystal quality

摘要

The unexpected room temperature ferromagnetism in well-crystallized lead titanate (PbTiO3) heteroepitaxial thin films is attributed to crystal quality, which is produced by mild hydrothermal epitaxy on strontium titanate (100) substrates. The morphological, structural and magnetic properties of these epitaxial films were examined by a variety of experimental techniques. In the growth process of PbTiO3 films with a perovskite structure, the nucleations appear as islands firstly and subsequent growth follows the layer-by-layer growth mode; simultaneously as increase of growth time the stress between films and substrates releases gradually, the lattices of films follow substrates at first and then the films obey their own lattices; the crystal quality is increasing during this growth process. Meanwhile the results of magnetic measurement reveal that our films have the unambiguous ferromagnetism, and the strength of the ferromagnetic component decreases monotonously as increasing crystal quality. In addition, the growth mechanism involved a dissolution-crystallization mechanism is exposed.