Diffusion of iron in the near-surface region of magnetite (001)

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 dif- fraction (LEED) studies of the ( √2× √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 Fe3O4-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 57Fe3O4 thin-films and a Fe3O4 (001) substrate after ultra high vacuum annealing at multiple temperatures. By exploiting the scattering length variation of 57Fe 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