Structure and magnetic properties of RCu4Mn (R=La-Gd)

We report the synthesis of new alloys of composition RCu4Mn for R=La, Ce, Pr, Nd, Sm, and Gd. The ternary compounds are found to crystallize in the hexagonal CaCu5-type structure of the RCu5 parent compounds, but for the Gd compound, this proved to be the high-temperature form. X-ray diffraction on a single crystal of GdCu4Mn was used to determine the site occupancies. The Mn ions substitute randomly on the Cu sublattice. The magnetization, electrical resistivity, and the heat capacity data show the absence of long range magnetic order in all the alloys in marked contrast to the parent RCu5 (R=Ce, Nd, Sm, and Gd) compounds which order magnetically. A complex, inhomogeneous magnetic state arising from the Cu-Mn disorder and 3d-3d and 3d-4f interactions is proposed.