Powder neutron thermodiffraction studies have allowed a precise determination of the magnetic phase diagrams of the $R{\mathrm{Mn}}_{12-x}{\mathrm{Fe}}_x$ series $({\mathrm{ThMn}}_{12}$ structure) with the occurrence of two different ordering temperatures $T_N$ and $T_C$ correlated, respectively, to antiferromagnetic and ferromagnetic couplings. At low iron contents $(x<~5)$ and for all R elements, the $3d$ metal sublattices exhibit antiferromagnetic (AF) configurations lying in the basal plane (a, b). The R magnetic moments order ferromagnetically at very low temperature only with c as an easy axis. For higher iron concentrations, the $3d$ magnetic moment arrangements change progressively with ferromagnetic (F) components collinear with the c axis superimposed on the AF components. For $x>\mathrm{}6,$ the Curie temperature $T_C$ coming from the F components of the $3d$ and R sublattices increases markedly. In addition, $T_N$ and the $3d$ AF components both decrease with x.

• Received 7 February 2001

DOI:https://doi.org/10.1103/PhysRevB.64.144426