Abstract
A polarized neutron scattering beamline at W3 beam port in Tsing Hua Open-pool Reactor (THOR) was constructed for polarized neutron reflectivity, neutron depolarization, and neutron diffraction. Polarized neutrons are powerful for measuring the magnetic properties of a magnetic material. Polarized neutron reflectivity is used to measure the magnetic depth profiles of a thin film system; and neutron depolarization is for measuring the magnetic correlation lengths, which are also called magnetic domains, in the range from sub-μm to sub-mm at THOR. For polarized neutron reflectivity at THOR, the dynamical range of the reflectivity measurement is limited to 2 orders of magnitude, only critical angle can be measured with a Q-resolution of 0.2 nm-1, i.e., the average magnetic moment can be measured but the depth profile of the sample is not possible to be obtained. Comparing to the reflectivity measurement on Ni80Fe20/Ru multilayer system at NRU reactor of Chalk River, Canada, a dynamical range of 5 orders is achieved. For neutron depolarization measurement, traditionally, only the observation of magnetic domain on the surface was used to explain the domain distribution in the interior of a bulk magnetic material, but rare experiments to measure the magnetic domain in the bulk were carried. Neutron depolarization can be used to determine the interior of a magnetic material non-destructively. A one-dimensional neutron depolarization experiment on NixFe100-x alloys was carried out at THOR. A magnetic correlation length of about 35 μm with an average induction of 240 Oe in the remnant state were deduced from the measured depolarization factor 0.79, and rotation angle 0.63 rad. Furthermore, this neutron scattering beamline is in process to be extended for doing 3-dimensional neutron depolarization experiments. The preliminary test on measuring the 3-dimensional neutron depolarization experiments is also reported.