Enhanced magnetodielectric coupling in strongly ferroic composite oxide film

Abstract

Lead-free all oxide composite thin films comprising ferromagnetic (FM) and ferroelectric (FE) phases are observed as promising candidates for multifunctional device applications. A series of composites having systematic replacement of FM La0.67Sr0.33MnO3 (LSMO) by FE-Na0.5K0.5NbO3 (NKN), all oxide composite thin films were optimally grown by pulsed laser deposition. While x-ray diffraction confirmed a systematic phase change from a rhombohedral to an orthorhombic structure, almost monodispersed grain size distribution and smooth surface topography were revealed by atomic force microscopy. Two-probe dielectric spectroscopy indicated a pronounced enhancement of real permittivity for 0.4 sample as compared to the pure FM and FE parent compounds. Similarly, an enhancement in the magnetodielectric permittivity revealed high values for intermediate composites. The enhancement in the dielectric and magnetoelectric coupling is suggested to be due to the magnetostriction effect in FM (LSMO), which induces stress that is in turn transferred to the FE (NKN) phase, leading to strong FM–FE coupling. X-ray photoelectron spectroscopy reveals the presence of Mn in +3 and +4 states in the FE–FM composites. The presence of these mixed valence states can be ascribed to the magnetic properties within the composites.