Structure and properties of the 5.5 K antiferromagnet EuAu2Ge2

A well crystallized sample of EuAti(2)Ge(2) was synthesized by arc-melting of the elements. The structure was refined on the basis of single crystal X-ray diffractometer data: ThCr2Si2 type, 14/mmm, a = 447.3(1), c = 1034.0(4) pm, wR2 = 0.0575, 148 F-2 values and 9 variables. The gold atoms have tetrahedral germanium coordination (261 pm Au-Ge). These AuGe4/4 tetrahedra share four common edges, leading to layers which are connected via Ge-Ge bonds (247 pm). The europium atoms fill cages of coordination number 16 within the [Au2Ge2](delta-) polyanion. Temperature dependent susceptibility measurements show a magnetic moment of 7.79(1)mu(B)/formula unit. Together with the Eu-151 Mossbauer spectroscopic data (isomer shift of -11.43 mm/s at 77K), the magnetic data point to stable divalent europium. EuAu2Ge2 orders antiferromagnetically at T-N1 = 5.5(1) K, followed by a spin-reorientation at T-N2 = 3.5 K. A metamagnetic step occurs around 20 kOe in the 4 K magnetization isotherm.