The interplay between superconductivity and Eu 2+ magnetic ordering in Eu(Fe 1−x Ir x ) 2 As 2 is studied by means of electrical transport and magnetic measurements. For the near optimally doped sample Eu(Fe 0.86 Ir 0.14 ) 2 As 2 , we witnessed two distinct transitions: a superconducting transition below 22.6 K which is followed by a resistivity reentrance caused by the ordering of the Eu 2+ moments. Further, the low field magnetization measurements show a prominent diamagnetic signal due to superconductivity, which is remarkable in the presence of a large-moment magnetically ordered system. The electronic structure for 12.5% Ir doped EuFe 1.75 Ir 0.25 As 2 is investigated along with the parent compound EuFe 2 As 2 . As compared to EuFe 2 As 2 , the doped compound has an effectively lower value of density of states throughout the energy scale with a more extended bandwidth and stronger hybridization involving Ir. Shifting of the Fermi energy and a change in band filling in EuFe 1.75 Ir 0.25 As 2 with respect to the pure compound indicate electron doping in the system.

Physical properties of polycrystalline CeCrGe3 and LaCrGe3 have been investigated by x-ray absorption spectroscopy, magnetic susceptibility χ(T ), isothermal magnetization M(H), electrical resistivity ρ(T ), specific heat C(T ) and thermoelectric power S(T ) measurements. These compounds are found to crystallize in the hexagonal perovskite structure (space group P63/mmc), as previously reported. The ρ(T ), χ(T ) and C(T ) data confirm the bulk ferromagnetic ordering of itinerant Cr moments in LaCrGe3 and CeCrGe3 with TC = 90 K and 70 K respectively. In addition a weak anomaly is also observed near 3 K in the C(T ) data of CeCrGe3. The T dependences of ρ and finite values of Sommerfeld coefficient γ obtained from the specific heat measurements confirm that both the compounds are of metallic character. Further, the T dependence of ρ of CeCrGe3 reflects a Kondo lattice behavior. An enhanced γ of 130 mJ/mol K 2 together with the Kondo lattice behavior inferred from the ρ(T ) establish CeCrGe3 as a moderate heavy fermion compound with a quasiparticle mass renormalization factor of ∼ 45.

We report on the crystal structure, physical properties and electronic structure calculations for the ternary pnictide compound EuCr2As2. X-ray diffraction studies confirmed that EuCr2As2 crystalizes in the ThCr2Si2-type tetragonal structure (space group I4/mmm). The Eu-ions are in a stable divalent state in this compound. Eu moments in EuCr2As2 order magnetically below Tm = 21 K. A sharp increase in the magnetic susceptibility below Tm and the positive value of the paramagnetic Curie temperature obtained from the Curie-Weiss fit suggest dominant ferromagnetic interactions. The heat capacity exhibits a sharp λ-shape anomaly at Tm, confirming the bulk nature of the magnetic transition. The extracted magnetic entropy at the magnetic transition temperature is consistent with the theoretical value Rln(2S + 1) for S = 7/2 of the Eu 2+ ion. The temperature dependence of the electrical resistivity ρ(T ) shows metallic behavior along with an anomaly at 21 K. In addition, we observe a reasonably large negative magnetoresistance (∼ -24%) at lower temperature. Electronic structure calculations for EuCr2As2 reveal a moderately high density of states of Cr-3d orbitals at the Fermi energy, indicating that the nonmagnetic state of Cr is unstable against magnetic order. Our density functional calculations for EuCr2As2 predict a G-type AFM order in the Cr sublattice. The electronic structure calculations suggest a weak interlayer coupling of the Eu-moments.

The magnetic and superconducting properties of 14% Ir-doped EuFe 2 As 2 are studied by means of dc and ac magnetic susceptibilities, electrical resistivity, specific heat and 151 Eu and 57 Fe Mössbauer spectroscopy (MS) measurements. Doping of Ir in EuFe 2 As 2 suppresses the Fe spin density wave transition and in turn gives rise to high temperature superconductivity below 22.5 K with a reentrant feature at lower temperature. Magnetization and 151 Eu Mössbauer data indicate that the Eu + 2 spins order magnetically below 18 K. 57 Fe MS studies show a line broadening in the absorption spectra below 18 K due to transferred hyperfine field from the magnetically ordered Eu sublattices. A pronounced λ-shape peak in the specific heat supports a second-order phase transition of Eu + 2 magnetic ordering with a strong ferromagnetic component, as confirmed by the magnetic field dependences of the transition. For a single crystal, the in-plane resistivity ρ ( ) ab and out-of-plane susceptibility ( χ c ) show superconducting transitions with zero resistance and diamagnetism, respectively. But the in-plane susceptibility ( χ ab ) does not show any diamagnetic shielding against external fields. The observed non-zero resistance in the temperature range 10-17.5 K, below the superconducting transition temperature, suggests the possible existence of a spontaneous vortex state in this superconductor.

A series of isotypes of ternary rare earth element-gold-tetrel intermetallic compounds have been synthesized, and their structures and properties have been characterized. R3Au7Sn3 (R = Y, La-Nd, Sm, Gd-Tm, Lu) crystallize with the hexagonal Gd3Au7Sn3 prototype (Pearson symbol hP26; P63/m, a = 8.110–8.372 Å, c = 9.351–9.609 Å, Vcell = 532.7–583.3 Å3, Z = 2), an ordered variant of the Cu10Sn3-type. Their structures are built up by GdPt2Sn-type layers, which feature edge-sharing Sn@Au6 trigonal antiprisms connected by trigonal R3 groups. Additional insertion of gold atoms leads to the formation of new homoatomic Au clusters, Au@Au6; alternatively, the structure can be considered as a superstructural polyhedral packing of the ZrBeSi-type. The magnetization, heat capacity, and electrical resistivity have been measured for R3Au7Sn3 (R = Ce, Pr, Nd, and Tb). All four compounds order antiferromagnetically with the highest TN of 13 K for Tb3Au7Sn3. In Ce3Au7Sn3, which has a TN of 2.9 K, the heat capacity and electrical resistivity data in zero and applied fields indicate the presence of Kondo interaction. The coefficient of the linear term in the electronic heat capacity, γ, derived from the heat capacity data below 0.5 K is 211 mJ/Ce mol K2, suggesting strong electronic correlations due to the Kondo interaction. The electronic structure calculations based on the projector augmented wave method for particular representatives of the series suggest different tendencies of the localized R-4f atomic orbitals (AOs) to hybridize with the valence states. LMTO-based bonding analysis on the nonmagnetic La3Au7Sn3 indicates that the integrated crystal orbital Hamilton populations are dominated by the heteroatomic Au–Sn contacts; however, contributions from La–Au and La–Sn separations are significant, both together exceeding 40% in the overall bonding. Homoatomic Au–Au interactions are evident for the Au@Au6 units, but, despite of the high atomic concentration of Au in the compound, they do not dominate the entire bonding picture

Results of muon spin relaxation (µSR) and neutron powder diffraction measurements on a reentrant superconductor Eu(Fe0.86Ir0.14)2As2 are presented. Eu(Fe0.86Ir0.14)2As2 exhibits superconductivity at Tc on ≈ 22.5 K competing with long range ordered Eu +2 moments below ≈ 18 K. A reentrant behavior (manifested by nonzero resistivity in the temperature range 10-17.5 K) results from an exquisite competition between the superconductivity and magnetic order. The zero field µSR data confirm the long range magnetic ordering below TEu = 18.7(2) K. The transition temperature is found to increase with increasing magnetic field in longitudinal field µSR which along with the neutron diffraction results, suggests the transition to be ferromagnetic. The neutron diffraction data reveal a clear presence of magnetic Bragg peaks below TEu which could be indexed with propagation vector k = (0, 0, 0), confirming a long range magnetic ordering in agreement with µSR data. Our analysis of the magnetic structure reveals an ordered magnetic moment of 6.29(5) µB (at 1.8 K) on the Eu atoms and they form a ferromagnetic structure with moments aligned along the c-axis. No change in the magnetic structure is observed in the reentrant or superconducting phases and the magnetic structure remains same for 1.8 K ≤ T ≤ TEu. No clear evidence of structural transition or Fe moment ordering was found.

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Interplay between a charge density wave (CDW) and superconductivity in LaPt2(Si1-x Ge x )2 has been studied by electrical transport and magnetic measurements. LaPt2Si2 crystallizes in CaBe2Ge2 type structure which shows a first order structural phase transition from tetragonal to orthorhombic accompanied by a CDW transition at 112 K and superconducting transition at around 1.22 K as confirmed by temperature dependence of resistivity and magnetic measurements. For 2[Formula: see text] doping of germanium, while the CDW temperature T CDW decreases, the superconducting transition temperature T C shows an increase. T CDW increases for 5[Formula: see text] doping of germanium and the superconducting transition decreases. These findings demonstrate the competing nature of a CDW and superconductivity.