Neutron-spin-echo from polarizing samples

Abstract

The dependence of the neutron spin polarization on the difference of the magnetic field integrals along the precession fields before and after the sample gives rise to a spin-echo signal. In neutron spin-echo (NSE) experiments with non-polarizing samples, a single spin-echo group is observed (or two in case of some magnetic sample systems). However, in NSE experiments using polarizing samples, three different groups appear: i) the spin rotation (SR) group, ii) the antiparallel echo (APE) group and iii) the parallel echo (PE) group. The echo groups contain information on the life time of the excitations from which the intermediate scattering function S(Q,t) can be derived. In this article, we discuss the basic strategies for NSE measurements using the 2-, 4-, and 20-point method. Finally, we report on quasi elastic NSE experiments on a polarizing magnetic sample MnSi, which stabilizes a single-handed spin spiral. Here, the overlap of the spin rotation and spin-echo group for small spin-echo times requires a measurement of the NSE signal over a wide range of phase angles.