The crystallographic structures and magnetic properties of $R\left({\mathrm{Fe}}_x{\mathrm{Mn}}_{1-x}{)}_{12}\hspace{0.5em}\right(R=\mathrm{H}\mathrm{o},\mathrm{Y};$ $x=0,$ 0.2, 0.5, 0.6, 0.7) have been studied using powder neutron diffraction and magnetic measurements. These compounds crystallize in a ${\mathrm{ThMn}}_{12}$-type structure. The rare earths occupy the $2a$ sites, and Fe and Mn atoms are distributed on three nonequivalent sites: $8i,$ $8j,$ and $8f.$ The Mn and Fe atoms are found to exhibit strong site preferences, with the $8i$ sites favoring Mn atoms and the $8f$ sites favoring Fe atoms. $\mathrm{Ho}(\mathrm{F}\mathrm{e},\mathrm{M}\mathrm{n}{)}_{12}$ compounds show a noncollinear magnetic structure within the Mn(Fe) sublattice. Spin-glass-like behavior has been observed in these two series. There are two characteristic temperatures for the $\mathrm{Ho}({\mathrm{Mn}}_{1-x}{\mathrm{Fe}}_x{)}_{12};$ one corresponding to the compensation of the ordered Ho and (Mn,Fe) magnetic moments, and the other to the ordering of the (Mn,Fe) lattice. The uncommon feature of two ordering temperatures in this compound is due to the weak rare-earth (R) transition-metal (T) interaction. The addition of Fe substantially modifies the magnetic interactions, thus increasing the ordering temperature and changing the type of magnetic order of the (Mn,Fe) sublattice.

• Received 29 April 2001

DOI:https://doi.org/10.1103/PhysRevB.65.064444