Spin-polarized positron annihilation measurements of polycrystalline Fe, Co, Ni, and Gd based on Doppler broadening of annihilation radiation

Kawasuso, Atsuo; Maekawa, Masaki; Fukaya, Yuki   ; Yabuuchi, Atsushi; Mochizuki, Izumi

The Doppler broadening of annihilation radiation (DBAR) spectra of Fe, Co, Ni and Gd polycrystals measured using spin-polarized positrons from a Ge-Ga source in magnetic fields exhibited clear asymmetry upon field reversal. The differential DBAR spectra between field-up and field-down conditions were qualitatively reproduced in calculations considering polarization of positrons and electrons. The magnitudes of the field-reversal asymmetry for the Fe, Co and Ni samples was approximately proportional to the effective magnetization. The magnetic field dependence of the DBAR spectrum for the Fe sample showed hysteresis that is similar to a magnetization curve. These results demonstrate that spin-polarized positron annihilation spectroscopy will be useful in studying magnetic substances.