Conventional ferroelectricity and magnetism are chemically contraindicated in ABO3-type perovskite-structure materials. The presence of unoccupied B d orbitals and the B d – O 2p orbital hybridization are considered as causing the polar ferroelectric distortion (e.g. Ti 3d – O 2p in BaTiO3) in many perovskite ferroelectrics, while the partially filled 3d or 5f orbitals are a prerequisite for magnetism. Moreover, ferromagnetic coupling is favored if the density of states at the Fermi level is high enough. Here we demonstrate that d0 ferromagnetism can be obtained at a charge-imbalanced interface between non-magnetic perovskite-structure ferroelectrics.
Epitaxial films of KTaO3,KNbO3, and NaNbO3are grown on Ti-terminated single-crystal SrTiO3 substrates. First-principles calculations show that the charge imbalance at the interfaces between these films and SrTiO3can introduce holes in SrTiO3 and induce a d0 ferromagnetic half-metallic 2D hole gas at the interfacial oxygen 2p orbitals. Presence of such an interfacial layer is experimentally detected from spectroscopic ellipsometry measurements. Magnetic investigations evidence ferromagnetic behavior at room temperature. The phenomenon makes it possible to obtain materials combining polar and magnetic ordering without any magnetic elements.
