Novel germanide Ce2RuGe: Synthesis, crystal structure and low-temperature physical properties

Novel ternary intermetallic phase Ce₂RuGe was synthesized via arc-melting of the constituents and subsequent annealing at 700°C. Its crystal structure was determined from the powder X-ray diffraction data collected at room temperature. The compound crystallizes in the orthorhombic structure of a new type: space group Pmmn (No. 59), lattice parameters: a = 4.38235(5) Å, b = 4.31818(5) Å, c = 9.91496(15) Å, Z = 2, Pearson symbol oP8. In the fully ordered unit cell of Ce₂RuGe, there are two crystallographic positions for Ce atoms, single site with Ru atoms, and single site with Ge atoms, each with the multiplicity of two. The crystal structure is built of infinite zigzag-like chains of the Ru and Ge atoms, propagating along the [010] direction. The essential feature is a very short interatomic distance between the Ce1 atoms and the Ru atoms being equal to 2.226(2) Å, while the Ce2–Ru distance is of regular length. This structural property gives rise to distinctive physical behavior of the compound that exhibits the coexistence of valence fluctuations associated with unstable 4f shell of the Ce1 ions and a long-range magnetic ordering that emerges in the Ce2 ions sublattice. As revealed by means of magnetization, heat capacity and electrical resistivity measurements, Ce₂RuGe orders antiferromagnetically at T_N = 12.0(1) K, and becomes ferromagnetic below T_C = 8.5(3) K.