Kinetics and Intermediate Phases in Epitaxial Growth of Fe3O4 Films from Deposition and Thermal Reduction

TL;DR

This study investigates the growth process, phase transitions, and kinetics of Fe3O4 films on Al2O3 substrates, revealing slow reduction kinetics but high crystallinity despite grain boundary issues.

Contribution

It introduces a combined pulsed laser deposition and thermal reduction method to grow high-quality Fe3O4 films and analyzes the phase transition kinetics.

Findings

Transition from Fe2O3 to Fe3O4 is slow due to high activation energy.

Fe3O4 films exhibit high crystallinity despite grain boundary mismatch.

Thermal reduction from α-Fe2O3 to Fe3O4 is kinetically limited.

Abstract

We have studied the growth of Fe3O4 (111) epitaxial films on Al2O3 (001) substrates using a pulsed laser deposition / thermal reduction cycle using an {\alpha}-Fe2O3 target. While direct deposition onto the Al2O3 (001) substrates results in an {\alpha}-Fe2O3 epilayer, deposition on the Fe3O4 (111) surface results in a {\gamma}-Fe2O3 epilayer. The kinetics of the transitions between Fe2O3 and Fe3O4 were studied by measuring the time constants of the transitions. The transition from {\alpha}-Fe2O3 to Fe3O4 via thermal reduction turns out to be very slow, due to the high activation energy. Despite the significant grain boundaries due to the mismatch between the unit cells of the film and the substrate, the Fe3O4 (111) films grown from deposition/thermal reduction show high crystallinity.