Buffer-layer effect on the ferromagnetism of manganite heterojunctions

Identifying and understanding interfacial magnetic structures of transition-metal oxides are of great importance not only for fundamental physics but also for potential device applications. Among them, manganite and ruthenate heterostructures have attracted considerable interest due to their intriguing interfacial properties induced by complex magnetic interactions. Here, we report the observation of dramatic buffer-layer dependence of ferromagnetism in ultrathin $(\mathrm{L}{\mathrm{a}}_{2/3}\mathrm{C}{\mathrm{a}}_{1/3})\mathrm{Mn}{\mathrm{O}}_{3}$ (LCMO)-based heterostructures. Though all trilayers are nonmetallic, the $\mathrm{SrRu}{\mathrm{O}}_{3}$-buffered LCMO trilayer exhibits enhanced ferromagnetism with the Curie temperature (${T}_{\mathrm{C}}\ensuremath{\sim}198\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) much higher than for $\mathrm{CaRu}{\mathrm{O}}_{3}$ (${T}_{\mathrm{C}}\ensuremath{\sim}99\phantom{\rule{0.16em}{0ex}}\mathrm{K}$)- and $\mathrm{SrTi}{\mathrm{O}}_{3}$ (${T}_{\mathrm{C}}\ensuremath{\sim}42\phantom{\rule{0.16em}{0ex}}\mathrm{K}$)-buffered counterparts, as well as the monolithic LCMO films with similar thickness. Combining atomically resolved scanning transmission electron microscopy imaging with electron energy loss spectroscopy mapping, we reveal that asymmetric interfaces exist in the $\mathrm{SrRu}{\mathrm{O}}_{3}$ buffered trilayer, with one exhibiting 1 unit-cell Sr diffusion into LCMO, which is responsible for the ${T}_{\mathrm{C}}$ enhancement. In contrast, charge transfer, which has been proposed previously as a possible mechanism, is excluded in this study. Our results may pave a promising road toward effective atomic control of interfacial magnetism.