We report on the magnetic properties of CeCoGe 3 by measuring the electrical resistivity, magnetic susceptibility, magnetization and specific heat, together with the magnetic properties of a reference compound LaCoGe 3 . The measurements were performed on a single crystal grown from a high-temperature solution using a third element, bismuth as flux. From the magnetic susceptibility and magnetization measurements, CeCoGe 3 is an antiferromagnet with a Neel temperature T N1 =21 K and undergoes two successive transitions T N2 =12 K and T N3 =8 K. The magnetization for H ∥[001] indicated a metamagnetic transition with three steps. We constructed a magnetic phase diagram from the magnetization measurements, which is very complex and is roughly similar to the previous result performed on a polycrystalline grain-aligned sample.

Unique Magnetic Phases in an Antiferromagnet CeCoGe3

A comparative chemical bonding analysis for the germanides La2 MGe6 (M=Li, Mg, Al, Zn, Cu, Ag, Pd) and Y2 PdGe6 is presented, together with the crystal structure determination for M=Li, Mg, Cu, Ag. The studied compounds adopt the two closely related structure types oS72-Ce2 (Ga0.1 Ge0.9 )7 and mS36-La2 AlGe6 , containing zigzag chains and corrugated layers of Ge atoms bridged by M species, with La/Y atoms located in the biggest cavities. Chemical bonding was studied by means of the quantum chemical position-space techniques QTAIM (quantum theory of atoms in molecules), ELI-D (electron localizability indicator), and their basin intersections. The new penultimate shell correction (PSC0) method was introduced to adapt the ELI-D valence electron count to that expected from the periodic table of the elements. It plays a decisive role to balance the Ge-La polar-covalent interactions against the Ge-M ones. In spite of covalently bonded Ge partial structures formally obeying the Zintl electron count for M=Mg2+ , Zn2+ , all the compounds reveal noticeable deviations from the conceptual 8-N picture due to significant polar-covalent interactions of Ge with La and M ≠ Li, Mg atoms. For M=Li, Mg a formulation as a germanolanthanate M[La2 Ge6 ] is appropriate. Moreover, the relative Laplacian of ELI-D was discovered to reveal a chemically useful fine structure of the ELI-D distribution being related to polyatomic bonding features. With the aid of this new tool, a consistent picture of La/Y-M interactions for the title compounds was extracted.

Polar-Covalent Bonding Beyond the Zintl Picture in Intermetallic Rare-Earth Germanides.

In this study we report the physical properties of the new ternary compound Ce2Rh3Ge that crystallizes in the rhombohedral, triple hexagonal MgCu2-type of structure. The electronic ground state properties of Ce2Rh3Ge were characterized by magnetic susceptibility, specific heat, electrical resistivity and thermal transport measurements. The results indicate the presence of short range magnetic interaction, probably of ferromagnetic origin below T(C)  =  4 K. The shape of χ(-1)(T) deviates from the Curie-Weiss behavior with a broad minimum at about T(min)(χ(-1))  =  450 K reminiscent of valence fluctuating cerium systems. At T  =  10 K, the magnetic part of the resistivity ρ(4 f) (T) exhibits a shallow minimum followed by increase of resistivity ρ(T) ∝  -lnT, which hints at a substantial Kondo screening effect. Ce2Rh3Ge belongs to a small group of strongly correlated cerium compounds in which the two competing effects of Kondo and RKKY interactions produce long-range magnetic order from strongly hybridized and intermediate-valent 4 f spins. At sufficiently low temperatures Ce2Rh3Ge scales well with the Kadowaki-Woods ratio A/γ(2) and the value of the Wilson ratio χ(T  →  0)/γ found for this compound classifies it as a mixed-valence compound. The presence of valence fluctuation and magnetic order it is rare for these attributes to be found simultaneously in same compound, in same temperature range. In our opinion a novelty of presented results of Ce2Rh3Ge is that this compound adds a new member to a small but growing class of systems bearing a strongly mixed- or intermediate-valent 4 f magnetic moment, but in which the lattice of spins nevertheless end up finding it possible to order magnetically.

http://iopscience.iop.org/article/10.1088/0953-8984/27/39/395601/pdf

Cooperative magnetic behaviour in the new valence fluctuating compound Ce2Rh3Ge.

Synthesis and structural characterization of the new compounds R2Zn1–xGe6 (R = La–Nd, Sm, Gd–Ho) is reported. A structural change was revealed along this series by careful analysis of single-crystal X-ray diffraction data. For light rare earths up to Tb the orthorhombic oS72-Ce2(Ga0.1Ge0.9)7 model was established; instead, the Dy compound represents a new structure type (P21/m, mP34, Z = 4, a = 7.9613(3) A, b = 8.2480(4) A, c = 10.5309(5) A, β = 100.861(1)°) being a superstructure of the mS36-La2AlGe6 prototype. The established structural models support the increase of Zn deficiency along the series, suggested by microprobe analysis, and its key role in governing structural changes. The vacancy ordering criterion was applied as a successful approach to find a general scheme including the structures of the ∼R2MGe6 compounds known up to now (R = rare-earth metal, M = transition metal, Mg, Al, Ga) and highlighting the subtle structural differences within this family. According to this scheme, these structure...

Vacancy ordering as a driving factor for structural changes in ternary germanides: the new R2Zn(1-x)Ge6 series of polar intermetallics (R = rare-earth metal).

Magnetic phase transitions and magnetocaloric effect in ternary rhombohedral Laves phases of Gd2Rh3Ge and Er2Rh3Ge

Publisher Summary This chapter reviews the current knowledge concerning the phase diagrams and crystal structures of ternary metal germanides with the R elements. It describes the isothermal sections and crystallographic characteristics of ternary compounds and outlines the experimental methods that have been utilized. While no phase diagram is available for the Ce–Ga–Ge system, the X-ray phase analysis of 180 ternary alloys indicated the formation of four ternary compounds in the Ce–Ga–Ge system. No phase diagram has been constructed for the ternary Ho–A1–Ge system; however, data on the formation and crystal structure of three compounds exist because of the independent investigations of research groups from L’viv University and Geneva University.

P.S. Salamakha

Papers

Chapter 173 Ternary rare-earth-germanium systems