Magnetic structures of Mn3−xFexSn2: An experimental and theoretical study

Abstract

We investigate the magnetic structure of Mn${}_{3\ensuremath{-}x}$Fe${}_{x}$Sn${}_{2}$ using neutron powder diffraction experiments and electronic structure calculations. These alloys crystallize in the orthorhombic Ni${}_{3}$Sn${}_{2}$ type of structure ($Pnma$) and comprise two inequivalent sites for the transition metal atoms (4$c$ and 8$d$) and two Sn sites (4$c$ and 4$c$). The neutron data show that the substituting Fe atoms predominantly occupy the 4$c$ transition metal site and carry a lower magnetic moment than Mn atoms. Four kinds of magnetic structures are encountered as a function of temperature and composition: two simple ferromagnetic structures (with the magnetic moments pointing along the $b$ or $c$ axis) and two canted ferromagnetic arrangements (with the ferromagnetic component pointing along the $b$ or $c$ axis). Electronic structure calculations results agree well with the low-temperature experimental magnetic moments and canting angles throughout the series. Comparisons between collinear and noncollinear computations show that the canted state is stabilized by a band mechanism through the opening of a hybridization gap. Synchrotron powder diffraction experiments on Mn${}_{3}$Sn${}_{2}$ reveal a weak monoclinic distortion at low temperature ($\ensuremath{\beta}\ensuremath{\sim}90.08$${}^{\ensuremath{\circ}}$ at 175 K). This lowering of symmetry could explain the stabilization of the $c$-axis canted ferromagnetic structure, which mixes two orthorhombic magnetic space groups, a circumstance that would otherwise require unusually large high-order terms in the spin Hamiltonian.