Structural, Superconducting and Magnetic Properties of La(3-x)R(x)Ni2B2N3 (R = Ce, Pr, Nd)

We report on structural and superconducting properties of La(3-x)R(x)Ni2B2N3 where La is substituted by the magnetic rare-earth elements Ce, Pr, Nd. The compounds Pr3Ni2B2N3 and Nd3Ni2B2N3 are characterized for the first time. Powder X-ray diffraction confirmed all samples R3Ni2B2N3 with R = La, Ce, Pr, Nd and their solid solutions to crystallize in the body centered tetragonal La3Ni2B2N3 structure type. Superconducting and magnetic properties of La(3-x)R(x)Ni2B2N3 were studied by resistivity, specific heat and susceptibility measurements. While La3Ni2B2N3 has a superconducting transition temperature Tc ~ 14 K, substitution of La by Ce, Pr, and Nd leads to magnetic pair breaking and, thus, to a gradual suppression of superconductivity. Pr3Ni2B2N3 exibits no long range magnetic order down to 2 K, Nd3Ni2B2N3 shows ferrimagnetic ordering below T_C = 17 K and a spin reorientation transition to a nearly antiferromagnetic state at 10 K.Comment: 5 pages, 4 figures, presented at 17. International Conference on Solid Compounds of Transition Elements, Annecy, France; 05.09.2010 - 10.09.201

Elucidating the lack of magnetic order in the heavy fermion CeCu2Mg

The final publication is available via https://doi.org/10.1103/PhysRevB.95.115146.Magnetic, transport, and thermal properties of CeCu2Mg are investigated to elucidate the lack of magnetic order in this heavy-fermion compound with a specific heat value, Cmag/T|T0 ≈ 1.2 J/mol K² and robust effective magnetic moments (μeff ≈ 2.46 μB). The lack of magnetic order is attributed to magnetic frustration favored by the hexagonal configuration of the Ce sublattice. In fact, the effect of magnetic field on Cmag/T and residual resistivity ρ0 does not correspond to that of a Fermi liquid (FL) because a broad anomaly appears at Tmax ≈ 1.2 K in Cmag(T)/T, without changing its position up to μoH=7.5 T. However, the flattening of Cmag/T|T0 and its magnetic susceptibility χ(T0), together with the T² dependence of ρ(T), reveal a FL behavior for T ≤ 2 K which is also supported by Wilson and Kadowaki-Woods ratios. The unusual coexistence of FL and frustration phenomena can be understood by placing paramagnetic CeCu2Mg in an intermediate section of a frustration-Kondo model. The entropy, Smag, reaches 0.87 Rln6 at T ≃ 100 K, with a tendency to approach the expected value Smag = Rln6 of the J=5/2 ground state of Ce3+

Structural and Physical Properties Diversity of New CaCu₅‑Type Related Europium Platinum Borides

Three novel europium platinum borides have been synthesized by arc melting of constituent elements and subsequent annealing. They were characterized by X-ray powder and single-crystal diffraction: EuPt₄B, CeCo₄B type, <i>P</i>6/<i>mmm</i>, <i>a</i> = 0.56167(2) nm, <i>c</i> = 0.74399(3) nm; Eu₃Pt₇B₂, Ca₃Al₇Cu₂ type as an ordered variant of PuNi₃, <i>R</i>3̅<i>m</i>, <i>a</i> = 0.55477(2) nm, <i>c</i> = 2.2896(1) nm; and Eu₅Pt₁₈B_6–<i>x</i>, a new unique structure type, <i>Fmmm</i>, <i>a</i> = 0.55813(3) nm, <i>b</i> = 0.95476(5) nm, <i>c</i> = 3.51578(2) nm. These compounds belong to the CaCu₅ family of structures, revealing a stacking sequence of CaCu₅-type slabs with different structural units: CaCu₅ and CeCo₃B₂ type in EuPt₄B; CeCo₃B₂ and Laves MgCu₂ type in Eu₃Pt₇B₂; and CaCu₅-, CeCo₃B₂-, and site-exchange ThCr₂Si₂-type slabs in Eu₅Pt₁₈B_6–<i>x</i>. The striking motif in the Eu₅Pt₁₈B_6–<i>x</i> structure is the boron-centered Pt tetrahedron [BPt₄], which build chains running along the <i>a</i> axis and plays a decisive role in the structure arrangement by linking the terminal fragments of repeating blocks of fused Eu polyhedra. Physical properties of two compounds, EuPt₄B and Eu₃Pt₇B₂, were studied. Both compounds were found to order magnetically at 36 and 57 K, respectively. For EuPt₄B a mixed-valence state of the Eu atom was confirmed via magnetic and specific heat measurements. Moreover, the Sommerfeld value of the specific heat of Eu₃Pt₇B₂ was found to be extraordinarily large, on the order of 0.2 J/mol K²

Superconductivity and magnetism in MPt4Ge12, M = Ca, Ba, Sr, Eu

X-ray powder data for Ba0.8Ca0.2Pt4Ge 12 and X-ray single crystal data for EuPt4Ge12 define cubic body-centered symmetry consistent with novel Ge-based skutterudites SrPt4Ge12 and BaPt4Ge12 (space group Im3). Structural and electron microprobe analysis investigations evidence a complete filling of the icosahedral cages without large atomic displacement parameters. Ba0.8Ca0.2Pt4Ge12 exhibits phonon-mediated superconductivity at Tc = 5.2 K. Density functional theory (DFT) calculations (LDA+U) carried out for EuPt 4Ge12 proved that Eu guest atoms strongly stabilize the compound in which the calculated density of states around the Fermi energy essentially consists of hybridized Ge 4p-like and Pt 5d-like states. Low temperature resistivity studies evidence magnetic ordering at Tm ? 1.7 K. Susceptibility measurements reveal a divalent state for europium, in excellent agreement with the DFT calculations