Spin polarization and magneto-dielectric coupling in Al-modified thin iron oxide films -microwave mediated sol-gel approach

Abstract

Production of single-phase materials with multifunctional properties is still a challenge faced by material scientists. In addition, obtaining high spin polarization efficiency in the materials that exhibit multifunctional properties is a big issue. A novel approach is suggested in this work for obtaining multifunctionality and spin polarization in the same material. This approach has combined the effect of microwave radiations and aluminum (Al) doping in iron oxide thin films during synthesis. Combined effect of microwave radiations and Al doping results in controlling / tuning the structural transitions in iron oxide thin films. Pristine and 2–10 wt% Al doped iron oxide thin films are prepared and studied in detail. Raman analysis shows that 2 and 4 wt% Al concentration results in γ-Fe2O3 + Fe3O4 phase with 71.3% and 64.5% of γ-Fe2O3 content, respectively. XRD and Raman analyses confirm the transition from γ-Fe2O3 to Fe3O4 thin films at Al concentrations of 6–10 wt%. Structural transformation shows that microwave radiations catalyzes that Al3+ions to occupy the vacancies on B sites of iron oxide thus, lead to the formation of Fe3O4. Observation of Verwey transition ~ 126 K also supports the transition in phases of iron oxide with increase in saturation magnetization from 251.3emu/cm3 (pristine films) to 405.6emu/cm3 (8 wt% Al concentration). High dielectric constant of ~ 135.5 (log f = 5.0) is observed for 8 wt% Al concentration. Conductivity and detailed impedance & modulus analyses depict Mott’s hopping phenomenon along with presence of different relaxation times. Coupling between magnetic and dielectric properties is observed at room temperature. Magnetoresistance curves indicate spin polarization efficiency of ~24%.