New Compounds of the ThCr2Si2-Type and the Electronic Structure of CaM2Ge2 (M: Mn–Zn)

Two new compounds were synthesized by heating mixtures of the elements at 975–1025 K and characterized by single-crystal X-ray methods. CaZn2Si2 (a=4.173(2) A˚, c=10.576(5) A˚) and EuZn2Ge2 (a=4.348(2) A˚, c=10.589(9) A˚) crystallize in the ThCr2Si2-type structure (space group I4/mmm; Z=2). Magnetic susceptibility measurements of EuZn2Ge2 show Curie–Weiss behavior with a magnetic moment of 7.85(5)μB/Eu and a paramagnetic Curie temperature of 10(1) K. EuZn2Ge2 orders antiferromagnetically at TN=10.0(5) K and undergoes a metamagnetic transition at a low critical field of about 0.3(2) T. The saturation magnetization at 2 K and 5.5 T is 6.60(5) μB/Eu. 151Eu Mo¨ssbauer spectroscopic experiments show one signal at 78 K at an isomer shift of −11.4(1) mm/s and a line width of 2.7(1) mm/s compatible with divalent europium. At 4.2 K full magnetic hyperfine field splitting with a field of 26.4(4) T is detected. The already known compounds CaM2Ge2 (M: Mn–Zn) also crystallize in the ThCr2Si2-type structure. Their MGe4 tetrahedra are strongly distorted with M=Ni and nearly undistorted with M=Mn or Zn. According to LMTO electronic band structure calculations, the distortion is driven by a charge transfer from M–Ge antibonding to bonding levels. [Copyright &y& Elsevier]