Search for Multi-Ferroic Manganites with Elongated Mn-O bonds

Development of multi-ferroic materials, where magnetism and ferroelectricity are strongly coupled near room temperature, is of fundamental technological and theoretical importance. Typically, both phenomena tend to be mutually exclusive because ferroelectricity is usually present for d$^{0}$ and magnetism for non-d$^{0}$ transition metals. By analogy to perovskite Ba$^{2+}$Ti$^{4+}$O$_{3}$ (d$^{0})$ for which [Ti-O] bonds are highly elongated beyond their equilibrium lengths resulting in Ti distortion out of the center of the TiO$_{6}$ octahedral unit, resulting in T$_{F}\sim $400 K ferroelectricity, we have projected that similar effect should be observed for the non-d$^{0}$ insulating and antiferromagnetic (T$_{N}\sim $240 K) perovskites of Mn$^{4+}$ (d$^{3})$. I will describe our search for such compounds guided by our ``tolerance factor design rules'' in the (Sr,Ba)Mn O$_{3}$ system for which strong multi-ferroic behavior was achieved near room temperature.