Structure and properties of the 5.5 K antiferromagnet EuAu2Ge2

Abstract

Abstract A well crystallized sample of EuAu2Ge2 was synthesized by arc-melting of the elements. The structure was refined on the basis of single crystal X-ray diffracto meter data: ThCr2Si2 type, I4/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] δ– polyanion. Temperature dependent susceptibility measurements show a magnetic moment of 7.79(1)μ B/formula unit. Together with the 151 Eu Mössbauer spectroscopic data (isomer shift of –11.43 mm/s at 77 K), 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.