Temperature and terahertz frequency dependence of the dielectric properties of Fe3O4 thin films deposited on Si substrate

TL;DR

This study investigates how temperature and terahertz frequency affect the dielectric and optical properties of Fe3O4 thin films on silicon, revealing that slight compositional changes significantly alter their THz optical behavior relevant for spintronic applications.

Contribution

It provides detailed analysis of the dielectric and optical conductivity variations of Fe3O4 films across temperatures and frequencies, highlighting the impact of Fe ion ratios on their properties.

Findings

Maximum optical conductivity at Fe2+/Fe3+ ratio of 0.54

Significant changes in dielectric properties with slight compositional variations

Optical properties differ drastically despite similar magnetization behavior

Abstract

The Fe$_3$O$_4$/Si films are considered to be promising materials for THz spintronic applications due to their high temperature magnetic transition and semiconducting properties. In this article, we present the real part of the dielectric constant ($\epsilon_1$) and the optical conductivity ($\sigma_1$) of Fe$_3$O$_4$ films of different thicknesses deposited on Si substrate (Fe$_3$O$_4$/Si) in the THz range at temperatures 2- 300 K. Although the magnetization of the films with thickness $\geq$ 115 nm shows a clear change at the Verwey transition temperature T$_v$ = 121 K, their optical properties in the THz frequency range are drastically different from each other. We have shown that $\sigma_1$ is maximum and $\epsilon_1$ is minimum when the Fe$^{+2}$/Fe$^{+3}$ ratio is equal to 0.54 which is the ratio of Fe+2/Fe+3 for pure Fe$_3$O$_4$. The $\sigma_1$ reduces and $\epsilon_1$ increases at all temperatures when the Fe$^{+2}$/Fe$^{+3}$ ratio deviates from 0.54. We have shown that a slight change in the Fe$^{+2}$/Fe$^{+3}$ ratio can induce large changes in the optical properties which shall have implications in the application of the Fe3O4 films in THz spintronics.