Development of Spin-Polarized Pulsed TEM

Recent nanointegration of magnetic storage and spintronic devices is expected to lead to the development of systems that can analyze magnetic and spin states with a nanometer-order spatial resolution. Development of a polarized transmission electron microscope (SPTEM) that employs a spin-polarized electron source (PES) has commenced at Nagoya University. A spin-polarized electron beam is extracted from a photocathode that has a negative electron affinity surface. The temporal profile of the electron beam can be modulated by varying the temporal profile of the driving laser. The SPTEM can obtain temporal and spatial information about spin. The design and construction of the PES were optimized for the SPTEM. A beam energy of less than 40 keV (a low energy for a TEM) was used because the spin interaction with condensed matter is very small compared with the Coulomb interaction. A polarized electron gun was realized in an extreme high vacuum by applying a high field gradient of 4 MV/m to the photocathode surface. A 40-keV polarized electron beam with sub-millisecond pulses was generated using a backside-excited photocathode. The illumination system of the TEM was designed with the aim of producing a spin-polarized electron beam. The system contains two components that rotate spin: one performs azimuthal rotation and the other performs in-plane rotation in the condenser magnet system. The SPTEM has the potential to dynamically generate magnetic-field images with high contrast and high temporal resolution.