  FeXMn1-XS (0 <x< 0.3) synthesized on the basis of {\alpha}-MnS are the novel
Mott-type substances with the rock salt structure. Neutron diffraction study
shows that the shift of the Neel temperature of these materials from 150 (x =
0) to 200 K (x = 0.29) under the action of chemical pressure (x) is accompanied
by a decrease in the cubic NaCl lattice parameters. The structural transition
with a change in crystal symmetry and a decrease in resistance before the
magnetic transition at x = 0.25 is found. Therefore, FeXMn1-XS are interesting
materials for both fundamental study of the interrelation between the magnetic,
electrical, and structural properties in systems with the strong electron
correlations of a MnO-type and application.
