Spin-dependent transmission of free electrons through ultrathin cobalt layers

We present an original technique to investigate spin-dependent electron interactions in ferromagnetic metals, and place it in the context of previous studies. Our technique is based on spin-polarized electron transmission through ultrathin, free-standing, metal foils. A longitudinally spin-polarized, quasimonoenergetic, free-electron beam impinges onto a ferromagnetic target consisting of a few atomic layers of cobalt sandwiched between gold layers, for an overall thickness of the order of 25 nm. It is remanently magnetized perpendicular to the film plane. The current transmitted through the foil is energy analyzed and its dependence on the relative orientation between the spin polarization of the primary beam and the magnetization direction of the cobalt layer is measured. The experiments are performed over a wide primary energy range, starting from the vacuum level of the target; the work function of the target can be lowered down to 2 eV by cesium deposition. We demonstrate a spin-filter effect, favoring the transmission of majority electrons. It is very large at low primary energy, when the electrons travel close to the 3d bands. Perspectives for compact-and highly discriminative spin detectors are discussed. (C) 1996 American Institute of Physics.