New Compounds of the ThCr 2Si 2-Type and the Electronic Structure of Ca M2Ge 2 ( M: Mn–Zn)

Abstract

Two new compounds were synthesized by heating mixtures of the elements at 975–1025 K and characterized by single-crystal X-ray methods. CaZn 2Si 2 ( a=4.173(2) Å, c=10.576(5) Å) and EuZn 2Ge 2 ( a=4.348(2) Å, c=10.589(9) Å) crystallize in the ThCr 2Si 2-type structure (space group I4/ mmm; Z=2). Magnetic susceptibility measurements of EuZn 2Ge 2 show Curie–Weiss behavior with a magnetic moment of 7.85(5) μ B/Eu and a paramagnetic Curie temperature of 10(1) K. EuZn 2Ge 2 orders antiferromagnetically at T N=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) μ B/Eu. 151Eu Mössbauer 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 Ca M 2Ge 2 ( M: Mn–Zn) also crystallize in the ThCr 2Si 2-type structure. Their MGe 4 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.