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.

Highlights

  • For further research of spintronics materials, the evaluation of electron spin is an important issue

  • When both positrons and electrons are spin-polarized, the positron-electron momentum distribution shows an asymmetry upon spin reversal

  • We have demonstrated that the Doppler broadening of annihilation radiation (DBAR) technique with spin-polarized positrons can be used for studying ferromagnetic band structures [1, 2]

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Summary

Introduction

For further research of spintronics materials, the evaluation of electron spin is an important issue. A new technique, “spin-polarized positron annihilation spectroscopy” (SP-PAS) method, is one of such advanced methods to evaluate electron spin polarization at the surface, interface and in the bulk. The pair-annihilation probability of a positron and an electron depends on their relative spin direction. Employing a longitudinally spin-polarized positron beam, longitudinal excess electron spins in magnetic substances under a strong magnetic field can be estimated. For such measurements, the maximum field strength of the magnetic field is important. There are some reports about construction of a magnet system for the in situ PAS measurements using a slow positron beam [8, 9], in most cases the maximum field strength was limited.

Beam development
DBAR measurements on ferromagnetic materials
Findings
Summary
Full Text
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