The spatial distribution of ferromagnetic moment in MnCO3

Measurements of the scattering from the ferromagnetic component of magnetic moment in MnCO 3 at 4.2 °K in applied fields of 1.57 and 7.0 kOe have been made using the polarized neutron method. An x-ray refinement of the structure was carried out to obtain accurate values for the positional parameter of the oxygen atom. From the results the distributions of the aligned spin density in the [1[1 over bar]10] projection have been calculated and these indicate that a significant proportion of the ferromagnetically aligned moment is not located within 1.2 Å of the manganese nucleus. The observed distributions have been separated into field-dependent and spontaneous parts, and the contribution of spin-orbit coupling to the spontaneous part has been estimated. Both moment distributions show considerable departures from spherical symmetry around the manganese atoms; the degree to which these can be explained by a simple theory of covalency is discussed.