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International audience; We demonstrate quantitative ballistic electron magnetic microscopy (BEMM) imaging of simple model Fe(001) nanostructures. We use in situ nanostencil shadow mask resistless patterning combined with molecular beam epitaxy deposition to prepare under ultra-high vacuum conditions nanostructured epitaxial Fe/Au/Fe/GaAs(001) spin-valves. In this epitaxial system, the magnetization of the bottom Fe/GaAs(001) electrode is parallel to the [110] direction, defining accurately the analysis direction for the BEMM experiments. The large hot-electron magnetoresistance of the Fe/Au/Fe/GaAs(001) epitaxial spin-valve allows us to image various stable magnetic configurations on the as-grown Fe(001) microstructures with a high sensitivity, even for small misalignments of both magnetic electrodes. The angular dependence of the hot-electron magnetocurrent is used to convert magnetization maps calculated by micromagnetic simulations into simulated BEMM images. The calculated BEMM images and magnetization rotation profiles show quantitative agreement with experiments and allow us to investigate the magnetic phase diagram of these model Fe(001) microstructures. Finally, magnetic domain reversals are observed under high current density pulses. This opens the way for further BEMM investigations of current-induced magnetization dynamics.

International audience; We report on ballistic electron-emission spectroscopy on high-quality Au(110)/GaAs(001) and Fe(001)/GaAs(001) Schottky contacts. For the Au(110)/GaAs(001) interface, the ballistic current is characterized by a strong electron injection in the L valley of the GaAs conduction band. This remarkable spectroscopic feature is absent for the Fe(001)/GaAs(001) interface. These observations are explained by the different electronic structures in the two metal layers, assuming conservation of the electron transverse momentum at the metal/semiconductor epitaxial interfaces. Conversely, this comparative study suggests that the technique can be used for the analysis of local electronic states propagating in the metal films.

International audience; The spatially resolved electronic structure of the epitaxial Au/MgO/GaAs(001) tunnel junction has been studied by ballistic electron emission microscopy. The Schottky barrier height of Au on the MgO/GaAs heterostructure is determined to be 3.90 eV, in good agreement with spatially averaged x-ray photoelectron spectroscopy measurements. Locally, two well-defined conduction channels are observed for electrons energies of 2.5 and 3.8 eV, i.e., below the conduction band minimum of the oxide layer. These conduction channels are attributed to band of defect states in the band-gap of the tunnel barrier related to oxygen vacancies in the MgO layer. These defect states are responsible for the low barrier height measured on magnetic tunnel junctions with epitaxial MgO(001) tunnel barriers.