Doppler broadening of annihilation radiation measurements on 3 and 4 ferromagnets using polarized positrons

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

We measured the Doppler broadening of annihilation radiation (DBAR) spectra of 3 (Fe, Co and Ni) and 4 (Gd, Tb and Dy) ferromagnets under magnetic field by using spin-polarized positrons from a Ge-Ga source. The results showed that the DBAR spectra of these metals have notable different magnetic field dependences. The differences among Fe, Co and Ni reflect that the upper minority spin bands of Fe and Co are nearly empty, while those of Ni are still mostly occupied. For the rare-earth metals, instead of the inner 4 electrons, 5d electrons that mediate the exchange interaction of the 4 electrons, are primarily responsible for magnetic field effects on the DBAR spectra. Furthermore, magnetic field effects on the DBAR spectra of Gd, Tb and Dy vanished above the Curie temperatures of the magnetic phase transition for these metals.