Interfacial Control of Ferromagnetism in Ultrathin SrRuO 3 Films Sandwiched between Ferroelectric BaTiO 3 Layers.

Interfaces between materials provide an intellectually rich arena for fundamental scientific discovery and device design. However, the frustration of magnetization and conductivity of perovskite oxide films under reduced dimensionality is detrimental to their device performance, preventing their active low-dimensional application. Herein, by inserting the ultrathin 4d ferromagnetic SrRuO layer between ferroelectric BaTiO layers to form a sandwich heterostructure, we observe the enhanced physical properties in ultrathin SrRuO films, including longitudinal conductivity, Curie temperature and saturated magnetic moment. Especially, the saturated magnetization can be enhanced to ~3.12 µ/Ru in ultrathin BaTiO/SrRuO/BaTiO trilayers, which is beyond the theoretical limit of bulk value (2 µ/Ru). This observation is attributed to the synergistic ferroelectric proximity effect (SFPE) at upper and lower BaTiO/SrRuO heterointerfaces as revealed by high-resolution lattice structure analysis. This SFPE in dual-ferroelectric interface cooperatively induces the ferroelectric-like lattice distortions in RuO6 oxygen octahedra and subsequent spin state crossover in SrRuO, which in turn accounts for the observed enhanced magnetization. Besides the fundamental significance of interface-induced spin-lattice coupling, our findings also provide a viable route to the electrical control of magnetic ordering, taking a step toward low-power applications in all-oxide spintronics.