Electrical, electronic and magnetic property correlation via oxygen vacancy filling and scaling-law analysis in LiFe5O8 thin films prepared by pulsed laser deposition

Abstract

We report on scaling law analysis of impedance data and the effect of thickness and oxygen vacancy filling on controlling the band edge parameters, and electrical, optical and magnetic properties in LiFe₅O₈ thin films. LiFe₅O₈ thin films with ordered α-phase are prepared at various thicknesses. The in-plane and out-of-plane saturation magnetization values are seen to increase from 152 to 225 emu cc⁻¹ and 118 to 175 emu cc⁻¹, respectively, with increasing the film thickness from 60 to 135 nm. The band gap value is seen to decrease from 2.64 eV to 2.24 eV and the separation between the Fermi energy and valence band edge energy is found to decrease from 0.53 eV to 0.18 eV. Further increase in thickness leads to an enhanced magnetization value and a decrease in the band gap towards the bulk material value. X-Ray photoelectron studies clearly indicate the oxygen vacancy filling and movement of the Fermi level towards the valence band edge with increasing thickness. The frequency and temperature dependent impedance of the LiFe₅O₈ thin films follows the time-temperature superposition principle (TTSP) scaling law and the conductivity is mainly attributed to the bulk grains. The DC conductivity of the LiFe₅O₈ thin film increases when the thickness is increased from 60 nm to 81 nm and decreases further with increasing the thickness to 103 nm. Changes in the conductivity values can be directly correlated with the bang gap values and grain size of the thin films. Precise control and tuning of the band edge parameters, and magnetic, electrical and electronic properties can be achieved by controlling the thickness and the oxygen vacancies in LiFe₅O₈ thin films.