Development of a Compact Angle Resolving Spin Polarized Photoemission Spectrometer for''Double Polarization'' X-Ray Photoelectron Diffraction Spectroscopy of Magnetic Nanostructures

X-ray Photoelectron Diffraction (XPD) is a well established technique for probing element and site specific surface structure of epitaxial thin films and nanostructures. Furthermore, recent studies have demonstrated that excitation of the photoelectrons via circularly polarized photons results in additional sensitivity to the element and site specific local magnetic order via the dipole selection rules. However the asymmetries involved in such experiments are very low, typically 1-2%. Calculations suggest that combining excitation via circularly polarized photons with spin polarized photoelectron detection into a complete ''double polarization'' experiment should lead to a 5-10 fold increase in asymmetry. However combining high angular resolution XPD with spin resolving capability poses significant experimental challenges. A new compact angle resolving spin spectrometer for conducting such double polarization experiments has recently been developed at the Advanced Light Source by the authors. This spectrometer combines a large (11 inch) diameter fixed hemispherical analyzer with a novel rotatable input lens system allowing data with ±1 degree angular resolution to be acquired for any combination of incident and emission angles, including normal incidence/normal emission (figure 1). The analyzer is equipped with both multichannel detection for high resolution (50meV) spin integrated spectroscopies, such as XPS and magnetic linear or circular dichroism, and a Mott detector capable of resolving the photoelectron spin polarization simultaneously along the two perpendicular axes of the rotational plane. Rapid switching between spin integrated and spin resolved modes is achieved by focusing the photoelectrons through a small hole in the detector of the hemispherical analyzer and into a compact mini-Mott detector situated immediately behind the channel plates