Magnetic properties of the RCoxGe2 (RÂ =Â Gd-Er) compounds

Magnetization, magnetic susceptibility, X-ray and neutron diffraction measurements down to 1.5 K were performed on polycrystalline RCoxGe2 (R = Gd-Er) samples, in which x = 0.4-0.5. All of them crystallize in the orthorhombic structure of the CeNiSi2-type. The compounds were found to order antiferromagnetically at low temperatures except for the Tb and Dy samples, in which no magnetic contributions were observed in the neutron diffraction patterns recorded at 1.5 K although transitions are visible in the temperature dependences of the magnetic susceptibility of these compounds. In the case of HoCo0.4Ge2 magnetic order appearing below the Néel temperature of 8 K is described by the propagation vector k = (1/2, 1/2, 0) and for the ErCoxGe2 compounds at 1.5 K the structure is described by k = (kx, kx, 0). The value of the kx component depends on the concentration x.