Enhancing the ferromagnetic interlayer coupling between epitaxial SrRuO3 layers

Abstract

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 ${\mathrm{SrRuO}}_{3}$ 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 ${\mathrm{SrRuO}}_{3}$-based multilayer. Previous studies reported that the coupling of two ${\mathrm{SrRuO}}_{3}$ 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 ${\mathrm{SrRuO}}_{3}$ layers separated by ultrathin ${\mathrm{LaNiO}}_{3}$ in epitaxial heterostructures grown on ${\mathrm{SrTiO}}_{3}$(100) single crystals. We found that FM ${\mathrm{SrRuO}}_{3}$ layers separated by 2 monolayers (MLs) thick ${\mathrm{LaNiO}}_{3}$ show weak FM interlayer coupling of about $106\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{J}/{m}^{2}$ at 10 K. The coupling becomes strongly FM for four MLs thick (about 1.6 nm) ${\mathrm{LaNiO}}_{3}$ spacers and the two ${\mathrm{SrRuO}}_{3}$ layers reverse their magnetization at a common value of the perpendicular magnetic field. This is likely due to a transition of the ${\mathrm{LaNiO}}_{3}$ spacer from insulating to metallic, as its thickness increases.