Low Dimensional Magnetic Lattice and Room Temperature Magneto(di)electric Effect in Polyanion Ruddlesden-Popper Iron Oxides.

We have shown a new design strategy which exploits different oxyanions in a Ruddlesden-Popper (RP)-type phase to modulate the local crystal structure and magnetic lattice. Material (Sr4Fe2(SO4)0.5O6.5) with the larger voluminous oxyanion (SO4, S-O distance = 1.49 Å) as separating blocks between magnetic FeO layers shows a two-dimensional magnetic lattice. A three-dimensional magnetic lattice and spin reorientation transition is observed for the Sr4Fe2(CO3)O6, having CO3 (C-O distance = 1.25 Å), a smaller oxyanion, as a separating layer. Using mixed oxyanions (SO4 and CO3) in the central perovskite block of the RP3 phase, we have demonstrated a facile strategy to modulate the local crystal structure. The modulated displacement of the magnetic cations, which can break the local centrosymmetry, is suggested to originate the magnetodielectric effect near the magnetic ordering temperatures (higher than room temperature). Further, all CO3 containing samples show magnetodielectric coupling below room temperature due to the spin reorientation transition. The room temperature magnetodielectric effect coupled to the targeted local modulation of the crystal structure by oxyanions (in the absence of second-order Jahn-Teller active "distortion centers") opens a new door to the design of new multifunctional materials with the possibility for the room temperature application.