Spontaneous positive exchange bias effect in SrFeO 3− x /SrCoO 3− x epitaxial bilayer

A novel phenomenon of spontaneous positive exchange bias (PEB) is reported in SrFeO 3− x /SrCoO 3− x epitaxial bilayer without undergoing any magnetic field treatment. When inserting a thick SrTiO 3 (STO) nonmagnetic spacer (about 6 nm) into the bilayer interface, this phenomenon still exists. Based on a series of testing means, the spontaneous PEB effect is supposed to be mainly related to short-range ferromagnetic (FM) exchange coupling at the interface when there is no STO spacer. As the STO interlayer reaches up to a certain thickness, short-range coupling interaction basically disappears. At this time, the long-range dipole field may be responsible for the coupling of the FM and antiferromagnetic (AFM) layer across the nonmagnetic STO and then leads to the same bias effect. Our discoveries provide a new way to realize and manipulate spontaneous exchange bias-based spintronics devices, such as magnetic recording heads and spin valves.