Atomic and electronic structure of twin growth defects in magnetite

Daniel Gilks,Keith Mckenna,Kosuke Matsuzaki,Zlatko Nedelkoski,Richard Evans,Demie Kepaptsoglou,Vlado K Lazarov,Leonardo Lari,Quentin Ramasse,Balati Kuerbanjiang,Tomofumi Susaki

doi:10.1038/srep20943

Abstract

We report the existence of a stable twin defect in Fe3O4 thin films. By using aberration corrected scanning transmission electron microscopy and spectroscopy the atomic structure of the twin boundary has been determined. The boundary is confined to the (111) growth plane and it is non-stoichiometric due to a missing Fe octahedral plane. By first principles calculations we show that the local atomic structural configuration of the twin boundary does not change the nature of the superexchange interactions between the two Fe sublattices across the twin grain boundary. Besides decreasing the half-metallic band gap at the boundary the altered atomic stacking at the boundary does not change the overall ferromagnetic (FM) coupling between the grains.

Highlights

We report the existence of a stable twin defect in Fe3O4 thin films
In this work we focus on a different type of structural boundary, the twin boundary, which we observed in thin films of Fe3O4
In this work we have shown that twin defects are present in thin film Fe3O4(111)/yttria-stabilised ZrO2 (YSZ)[111]

Summary

Experimental Methods

Fe3O4 films of 100 nm thickness have been grown on [111] oriented yttria-stabilised zirconia (YSZ) by pulsed laser deposition (PLD) with a KrF excimer laser incident on a stoichiometric sintered Fe3O4 target. In order to minimize the effect of elastic scattering in the EELS signal, the EELS spectra were acquired at a relatively large collection angle (36 mrad). The relative thickness of the sample in the areas of interest did not exceed 0.5∙t/λ (where t the thickness and λ the electron free mean path for 100kV electron beam), as determined by using low loss EELS spectrum images of identical dimension, acquired subsequently in the exact same areas as the core-loss data. In order to assess the effect of multiple scattering in the EELS signal, low loss EELS spectrum images were systematically acquired at the same areas as the core loss signal. Post mortem images were acquired immediately after each EELS acquisition to assess possible beam damage effects. In order to minimise the electron beam damage electron dose distributed EELS SMART acquisition technique was employed, yielding very similar results (see Figure S5)

Theoretical Methods

Author Contributions

Additional Information