  The origin of the spin-glass state in (Fe,Sn)4N alloys is studied on the
basis of a Heisenberg Hamiltonian with parameters derived from first principles
within the magnetic force theorem applied in the framework of the disordered
local moments method and local spin-density approximation. We show that in the
alloy concentration range where the spin-glass state is stable only one Fe
sublattice is intrinsically magnetic and the interatomic exchange magnetic
interactions are essentially short ranged due to effects of chemical and
magnetic disorder. The magnetic Fe atoms with well-localized spin moments are
randomly distributed over the nongeometrically frustrated simple cubic lattice.
The magnetic frustration, which generally is believed to be an essential
ingredient of the spin-glass state formation condition, may occur only due to
the competition of the two nearest-neighbor interactions. We thus argue that
(Fe,Sn)4N is a rare example of a spin-glass system where the mechanism of
spin-glass state formation might be studied in the framework of the minimal
random-site model on a simple cubic lattice with competing interactions, while
the effects of the geometrical frustration can be excluded.
