Spin reorientation and magnetodielectric anomalies in FexO1+x (x = 2,3) thin films-effect of microwave radiations

Abstract

Materials with remarkable magnetodielectric properties are promising candidates for multifunctional devices. Microwave assisted sol-gel method is adopted to synthesize iron oxide thin films under microwave irradiations of 180 W-1000 W. Ferromagnetic response of sols is observed at 360–450 W, 630 W and 720 W powers, while superparamagnetic behavior is obtained at 810 W-1000 W. Films prepared using sols synthesized at 180 W, 270 W and 540 W exhibit amorphous nature. α-Fe2O3 phase is observed at microwave power (MW) of 360 W-450 W. γ-Fe2O3 phase is observed at MW of 630 W and 720 W and Fe3O4 phase is observed at 810–1000 W. Highest saturation magnetization of 45.23emu/cm3, 248.403emu/cm3 and 419.43emu/cm3are observed for α-Fe2O3, γ-Fe2O3 and Fe3O4, respectively. The transition of Verwey in Fe3O4 thin film is observed at ∼ 115.2 K, whereas γ-Fe2O3 phase does not show any such variation. Further, α-Fe2O3 phase show spontaneous magnetization at low temperatures from FC/ZFC curves. Highest dielectric constant of ∼ 54.26, 84.19 and 121.34 (log f = 5.0) are observed for α-Fe2O3, γ-Fe2O3 and Fe3O4, respectively. Magnetodielectric coupling (MDE) of ∼ −3.9%, −5.1% and −7.5% is obtained for α-Fe2O3, γ-Fe2O3 and Fe3O4 thin films. Fe3O4 phase is found to exhibit peculiar MDE coupling with respect to other phases, revealing exotic magnteodielectric coupling anomalies.