Doppler-broadening of annihilation radiation spectroscopy under high magnetic field using a longitudinally spin-polarized slow positron beam

Abstract

A spin-polarized positron beam generated using a ²²Na source, solid neon moderator and magnetic lens was developed. The beam diameter, beam flux and spin polarization were 0.5 mm, 1 × 10⁵ e⁺ s⁻¹ and 27%, respectively. An electromagnet system, which can generate ±1 T magnetic field, was also developed and equipped with the beam apparatus. Using this apparatus, Doppler broadening of annihilation radiation spectra under a high magnetic field were measured for bulk polycrystalline Fe, Co, and Ni samples and a thin film Co₂MnSi sample. These spectra showed a clear asymmetry upon field reversal.