Chemical synthesis of nanoporous EuTiO3 thin film and induced ferromagnetism

Porosity was chemically introduced into a EuTiO3 thin film to distort EuTiO3 and induce ferromagnetism. Scanning electron microscope images confirmed the successful preparation of a crack-free film with nanopores. High magnification transmission electron microscopy revealed that the framework was well crystallized and the surface was amorphous, forming a core-shell structure. Although bulk EuTiO3 is G-type antiferromagnetic, the obtained film had ferromagnetism. A fast Fourier transform mapping method revealed that a biaxial strain sufficient to induce ferromagnetism was created inside the crystallized framework core. The amorphous shell may contribute to the ferromagnetism because the enlarged crystal field splitting enhanced the ferromagnetic interaction between the nearest-neighboring Eu2+ by indirect exchange coupling between 4f spins via the 5d state of Eu2+ and the interaction between Eu spins by freely moving Ti 3d electrons originating from the oxygen vacancy.