The relationship between structural and magnetic properties in stoichiometric pyrrhotite Fe7S8 has been investigated using variable-temperature neutron-diffraction data. Below its magnetic ordering temperature, TN=598(5) K, Fe7S8 exhibits a monoclinic 4C structure, related to that of NiAs, in which fully occupied cation layers alternate with cation-deficient layers. The magnetic structure consists of ferromagnetically aligned layers, with antiferromagnetic coupling of adjacent layers. The ordered moment of 3.16(1)µB at 11 K is directed at an angle of 29° to the layers. The magnetic transition is accompanied by a structural transformation from the monoclinic 4C structure to a hexagonal cation-deficient NiAs structure, in which the vacancies are statistically distributed between all layers. Although the 4C structure is recovered on cooling through the magnetic transition, the resultant phase exhibits a significant degree of intralayer cation disorder.
|Journal||Physical Review B: Condensed Matter and Materials Physics|
|Publication status||Published - Jul 2004|