Physique du Solide présentée par:

Spin dependent hot electron transport and nanoscale imaging of metal/silicon structures In this work, we experimentally study spin-dependent hot electron transport through metallic multilayers (ML), containing single magnetic layers or “spin-valve” (SV) trilayers. For this purpose, we have set up a ballistic electron emission microscope (BEEM), a three terminal extension of scanning tunnelling microscopy on metal/semiconductor structures. The implementation of the BEEM requirements into the sample fabrication is described in detail. Using BEEM, the hot electron transmission through the ML’s was systematically measured in the energy range 1-2 eV above the Fermi level. By varying the magnetic layer thickness, the spin-dependent hot electron attenuation lengths were deduced. For the materials studied (Co and NiFe), they were compared to calculations and other determinations in the literature. For sub-monolayer thickness, a non uniform morphology was observed, with large transmission variations over subnanometric distances. This effect is not yet fully understood. In the imaging mode, the magnetic configurations of SV’s were studied under field, focussing on 360 domain walls in Co layers. The effects of the applied field intensity and direction on the DW structure were studied. The results were compared quantitatively to micromagnetic calculations, with an excellent agreement. From this, it can be shown that the BEEM magnetic resolution is better than 50 nm. Keyword(s): magnetic multilayers metal/semiconductor structures spin-dependent transport hot electrons STM-BEEM magnetic microscopy micromagnetic calculations 137 te l-0 03 54 76 9, v er si on 1 20 J an 2 00 9