Thickness tuneable dielectric, optical and magnetic response of lithium ferrite thin films deposited by pulsed laser deposition

Abstract

Spinel ferrite thin films are in demand for efficient device applications due to their promising properties. So, improvement of their magnetic and dielectric behavior for miniaturizing devices is necessary. The lithium ferrite thin films (single phase with a spinel structure space group - P4132) are deposited at 700 °C on Pt(111)/Ti/SiO2/Si and quartz substrates with different thicknesses. The calculated d – spacing of 240 nm from the selected area electron diffraction pattern is in good agreement with the X-ray diffraction results. X-ray photoelectron spectroscopy confirmed the presence of Li, O, and other valance states of Fe ions. The microstructure of the films revealed the formation of uniform grains with well-separated grain boundaries. Further, the root-mean-square surface roughness is decreased from 11 nm (160 nm) to 9 nm (240 nm) and increased only for 300 nm. The optical bandgap is found to be in the range of 2.58 ‒ 2.30 eV and decreaded with the increase in film thickness. The saturation magnetization in-plane and out-of-plane is reduced monotonically with an increase in thickness attributed to the decrease in the compressive strain. The coercivity increased with the increase in film thickness. The dielectric constant improved, whereas dielectric loss decreased with an increase in thickness. The impedance spectra revealed the contribution of grain boundary is reduced with the increase in film thickness and is analyzed using the equivalent circuit model. The involved conduction process is well fitted with the Mott's variable range hopping mechanism. The obtained results demonstrate that desired response can be obtained by tailoring the film thickness for the microwave and magnetic devices such as magnetic oxide semiconductor.