Setup for polarized neutron diffraction using a high-Tc superconducting magnet on the instrument POLI at MLZ and its applications

Abstract

A new polarized neutron diffraction setup has been developed for the hot neutron single crystal diffractometer POLI at the Maier-Leibnitz Zentrum (MLZ) in Germany. This setup consists of a 3He spin filter cell for polarization, a Mezei type double coil flipper optimized for short-wavelength neutrons, and a new high-Tc superconducting magnet producing fields up to 2.2 T. Because the magnet provides a symmetric field configuration, a dedicated guide field system was designed in order to avoid neutron depolarization in the zero-field node. The polarization transport efficiency of the whole setup was numerically simulated and optimized using COMSOL Multiphysics®. The polarization losses between the polarizer and the sample were confirmed to be smaller than 1.5% over the total field range of the magnet and the stray fields of the magnet did not affect the relaxation time T 1 of the 3He spin filter polarizer. First experiments with antiferromagnetic and paramagnetic samples using the new setup have been successfully performed. Using the CCSL software, a reconstruction of the field induced spin density distribution in the weak ferromagnet MnCO3 was performed in the paramagnetic state. Our results show the high performance and good resolution of the new setup.