Development of a new neutron 4-circle diffractometer and application to the crystal and magnetic structure of MnF₂

We have developed a four-circle diffractometer for a single-crystal sample at the guide-hall of the reactor JRR-3M at JAERI (Japan Atomic Energy Research Institute). We have also developed a horizontally and vertically bent monochromator with silicon crystals. The wavelength of the neutron is 1.57 Å, and the maximum scattering angle of the detector is 156°. To evaluate the apparatus, we investigated crystal and magnetic structures of manganese fluoride MnFa. A very good R factor is obtained for structure analysis, and the 3d-electron density, which is carrying spins, is obtained by analyzing the magnetic structure factors. The structure parameters obtained compare well to the reported values, and the imaging of the spin density indicates the powerfulness of the single-crystal neutron experiments.