Enhancing the ferromagnetic interlayer coupling between epitaxial SrRuO3 layers

Magnetic interlayer coupling is a key ingredient in designing magnetic multilayers with functionalities that reach out to the realm of applications. In epitaxial ferromagnetic (FM) oxide multilayers, the magnetic interlayer coupling is, however, less studied and its prediction is often a challenging task. Ultrathin FM SrRuO3 epitaxial films with perpendicular magnetic anisotropy, interfaced with suitable oxides, may be susceptible of forming skyrmions. Hence, a strong FM interlayer coupling would be beneficial to achieve uniform switching behavior of a SrRuO3-based multilayer. Previous studies reported that the coupling of two SrRuO3 layers separated by a non-FM oxide spacer is at best weakly FM and the two FM layers switch at markedly different fields. Here we study the magnetic interlayer coupling between two FM SrRuO3 layers separated by ultrathin LaNiO3 in epitaxial heterostructures grown on SrTiO3(100) single crystals. We found that FM SrRuO3 layers separated by 2 monolayers (MLs) thick LaNiO3 show weak FM interlayer coupling of about 106μJ/m2 at 10 K. The coupling becomes strongly FM for four MLs thick (about 1.6 nm) LaNiO3 spacers and the two SrRuO3 layers reverse their magnetization at a common value of the perpendicular magnetic field. This is likely due to a transition of the LaNiO3 spacer from insulating to metallic, as its thickness increases.