Neutron and X-Ray Diffraction Study of the Low-Temperature Chemical and Magnetic Structure of Alpha-Manganese

The low-temperature chemical and magnetic structures of antiferromagnetic $\alpha$-manganese have been investigated. High-resolution neutron powder data indicate that the chemical and the magnetic unit cell are identical in size. An x-ray powder study of 60 reflections at 77 and 4 °K indicates no significant changes at low temperature in the atomic coordinates. Fourteen independent magnetic reflections measured at 77, 50, and 4 °K were used to determine the signs and magnitudes of the four magnetic moments for a collinear spin model. At 4 °K, they are 1.72±0.19, 1.46±0.08, 1.11±0.04, and 0.02±0.05 in units of ${\mu }_B$ for atoms I, II, III, and IV, respectively. The fit of the observed and calculated magnetic intensities indicates the need for a less restricted model for the magnetic structure. These results are compared with those of other experiments.