Electron transmission through ultra-thin metal layers and its spin dependence for magnetic structures

Abstract

We present a new set of experiments in which the attenuation of a ‘monoenergetic’, possibly spin-polarized, free-electron beam is measured by direct transmission through an ultra-thin metal layer. The self-supported metal target is either a reference gold sample or a ferromagnetic structure. The overall thickness is of the order of 25 nm. The magnetic structure consists of a 1 nm thick cobalt film sandwiched between 21-2 nm thick gold layers, with perpendicular magnetization. Measurements are performed throughout a wide energy range, with incident electron energies 2–1000 eV above the Fermi level. The transmission of the gold layer is found to be substantially higher than that of the magnetic structure. In the latter case, at low energy, close to the clean surface vacuum level, we find that the majority spin electrons are more easily transmitted than the minority spin electrons. Cesium deposition on the exit side or on both sides of the target increases the overall transmitted current by almost an order of magnitude. In the case of the magnetic structure, this also increases the transmission spin asymmetry from 16 to about 40%. Such structures appear to be well-suited to the construction of convenient and compact spin-detectors.