Abstract
The complex and intriguing properties of the ferrimagnetic half metal magnetite (Fe3O4) are of continuing fundamental interest as well as being important for practical applications in spintronics, magnetism, catalysis and medicine. There is considerable speculation concerning the role of the ubiquitous antiphase boundary (APB) defects in magnetite, however, direct information on their structure and properties has remained challenging to obtain. Here we combine predictive first principles modelling with high-resolution transmission electron microscopy to unambiguously determine the three-dimensional structure of APBs in magnetite. We demonstrate that APB defects on the {110} planes are unusually stable and induce antiferromagnetic coupling between adjacent domains providing an explanation for the magnetoresistance and reduced spin polarization often observed. We also demonstrate how the high stability of the {110} APB defects is connected to the existence of a metastable bulk phase of Fe3O4, which could be stabilized by strain in films or nanostructures.
Highlights
The complex and intriguing properties of the ferrimagnetic half metal magnetite (Fe3O4) are of continuing fundamental interest as well as being important for practical applications in spintronics, magnetism, catalysis and medicine
We present the density of states (DOS) calculated at the density functional theory (DFT) level rather than the DFT þ U level since it provides a better representation of the half-metallic electron structure above the Verwey transition, which is most relevant for spintronic devices and electron transport spin polarization measurements
The predicted atomic structure of the most stable antiphase boundary (APB) defect has subsequently been verified in all three dimensions by high-resolution electron microscopy highlighting the predictive power of our theoretical approach
Summary
The complex and intriguing properties of the ferrimagnetic half metal magnetite (Fe3O4) are of continuing fundamental interest as well as being important for practical applications in spintronics, magnetism, catalysis and medicine. While the presence of APB defects in Fe3O4 is well known (for example, from electron or scanning probe microscopy studies15,16) precise determination of their atomic-scale structure and magnetic properties has proved challenging. The presence of AF superexchange interactions in APBs has largely been inferred from crystallographic arguments rather than from direct experimental or theoretical evidence[17,18] While these simple models are often very useful, they bring no information on the relative stability or electronic properties of APB defects, which presents a significant obstacle to developing a deeper understanding of their role to optimize materials for applications. We employ first principles-based theoretical modelling to predict the detailed atomic structure, magnetic and electronic properties of stable APB defects in magnetite. Following a thorough theoretical screening of structures, we identify two possible {110} APB structures both of which are [110] [001]
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