These Δ1 states are fully spin-polarized and are responsible for the observed high magnetocurrent in these heterostructures. Among these k|| ≈ 0 states, conservation of the electron wave-function symmetry at the Fe/Au epitaxial interfaces additionally selects electrons with the Δ1 symmetry. Above the Schottky barrier height, hot-electrons are collected in the Г valley of GaAs selecting thus only electrons with a transverse momentum (k║) close to zero. The electron wave function transmission at the interfaces should satisfy two selection rules: the transverse momentum (k║) of the electron wave vector and the symmetry of the electron wave function should be conserved. In the metallic thin films, electrons propagate as Bloch states. In this epitaxial heterostructure, the hot electron beam is mainly spin-polarized at the interfaces due to band structure effects. This high magnetocurrent value is observed to be almost independent of the Fe layers thickness, and thus can not be explained by the spin asymmetry of the electron attenuation length in the iron layers. BEMM measurements on epitaxial Fe/Au/Fe/GaAs(001) samples demonstrate hot electron magnetocurrent as high as 500% at room temperature. The first part of this work consists in the study of a planar heterostructures.

The measurement of the ballistic electron current collected at the back of the substrate under magnetic field gives access to the local magnetoconductance properties of the sample.

In these experiments, hot electrons are injected from an STM tip through the metallic base. During this thesis work, we studied by ballistic electron magnetic microscopy (BEMM) the hot electron magnetotransport properties of epitaxial Fe/Au/Fe/GaAs(001) heterostructures.

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