# Real-time monitoring of the structure of ultra thin Fe$_3$O$_4$ films during growth on Nb-doped SrTiO$_3$(001)

## TL;DR

This study uses in-situ x-ray diffraction to monitor the real-time growth and strain evolution of ultra-thin Fe$_3$O$_4$ films on SrTiO$_3$ substrates at different temperatures, revealing strain behaviors and sublattice occupancy changes.

## Contribution

It introduces real-time x-ray diffraction monitoring during magnetite film growth, providing new insights into strain development and atomic site occupancy at various temperatures.

## Key findings

- Higher growth temperature leads to relaxed vertical lattice constant.
- Lower temperature results in strong vertical compressive strain.
- A decrease in A-site occupancy correlates with increased temperature.

## Abstract

In this work thin magnetite films were deposited on SrTiO$_3$ via reactive molecular beam epitaxy at different substrate temperatures. The growth process was monitored in-situ during deposition by means of x-ray diffraction. While the magnetite film grown at 400$^\circ$C shows a fully relaxed vertical lattice constant already in the early growth stages, the film deposited at 270$^\circ$C exhibits a strong vertical compressive strain and relaxes towards the bulk value with increasing film thickness. Furthermore, a lateral tensile strain was observed under these growth conditions although the inverse behavior is expected due to the lattice mismatch of -7.5%. Additionally, the occupancy of the A and B sublattices of magnetite with tetrahedral and octahedral sites was investigated showing a lower occupancy of the A sites compared to an ideal inverse spinel structure. The occupation of A sites decreases for a higher growth temperature. Thus, we assume a relocation of the iron ions from tetrahedral sites to octahedral vacancies forming a deficient rock salt lattice.