Speaker
Description
The mobility of Fe in magnetite is a key ingredient towards a better understanding of its defect structure and resulting properties. For nanoparticles, which find a range of applications in medicine, spintronics, material science and catalysis, the near-surface is particularly important. Recent scanning tunnelling microscopy (STM) and low energy electron diffraction (LEED) studies of the ($\sqrt{2}$×$\sqrt{2}$)R45° reconstructed (001) surface suggested a subsurface vacancy stabilisation model for this surface, later proved by surface x-ray diffraction (SXRD) [1,2]. Low energy electron microscopy (LEEM) experiments under catalytic conditions showed a regrowth process of $\text{Fe}_3\text{O}_4$-layers on (001) surfaces [3]. These results point towards an interesting interplay between cation vacancy formation and diffusion.
We present the results of iron exchange at the interface between $^{57}\text{Fe}_3\text{O}_4$ thin-films and a $\text{Fe}_3\text{O}_4$ (001) substrate after ultra high vacuum annealing at multiple temperatures. By exploiting the scattering length variation of $^{57}\text{Fe}$ and natural Fe, its interdiffusion across the film-substrate interface is characterized by neutron reflectometry at MARIA at MLZ [4].
The results on growth and diffusion are complemented by x-ray reflectometry data.
[1] Bliem, R. et al. Science. 346, 1215 (2014)
[2] Arndt, B. et al. Surf. Sci. 653, 76 (2016)
[3] Nie, S. et al., J. Am. Chem. Soc. 135, 10091 (2013)
[4] Schmidt, H. et al. Adv. Eng. Mat. 11, 446 (2009)
