Polarized neutron radiography with a periscope

The interaction of the magnetic moment of the neutron with magnetic fields provides a powerful probe for spatially resolved magnetisation measurements in magnetic materials. We have tested a periscope as a new type of polarizer providing neutron beams with a high polarization and a low divergence. The observed inhomogeneity of the beam caused by the waviness of the glass substrates was quantified by means of Monte-Carlo simulations using the software package McStas. The results show that beams of high homogeneity can be produced if the waviness is reduced to below 1.0·10^-5 rad. Finally, it is shown that radiography with polarized neutrons is a powerful method for measuring the spatially resolved magnetisation in optically float-zoned samples of the weak itinerant ferromagnet Ni₃Al, thereby aiding the identification of the appropriate growth parameters.