Crystal structures and magnetic properties of CeAu4Si2 and CeAu2Si2

Single crystals of CeAu4Si2 and CeAu2Si2 have been grown out of ternary fluxes rich in Au, and the former, also by sintering the stoichiometric composition at 750 °C. The single-crystal X-ray refinement result for CeAu4Si2 is orthorhombic, Cmmm (No. 65, Z=2), different from a tetragonal result found from an X-ray powder diffraction refinement [H. Nakashima, et al., J. Alloys Compds. 424 (2006) 7]. For CeAu2Si2, this is the first report of the stoichiometric crystalline phase, in the known tetragonal I4/mmm structure. The anisotropic field- and temperature-dependent magnetizations, as well as specific heat and resistivity data are compared. Although both compounds have related structural packing, they present unique magnetic features. CeAu2Si2 is a typical antiferromagnet with TN=8.8(1) K and CeAu4Si2 features a ferromagnetic component below Tc=3.3(1) K. Both phases have effective moments close in value to that of free Ce3+.