A series of four homologous silicides have been discovered during systematic explorations in the central part of the La-Ni-Si system at 1000 °C. All compounds LaNiSi ( = 3; = 28.8686(8), = 4.
View Article and Find Full Text PDFThe crystallographic and transport properties of thin films fabricated by pulsed laser deposition and belonging to the Sm(FeNi)Sbfilled skutterudite system were studied with the aim to unveil the effect exerted by temperature and duration of thermal treatments on structural and thermoelectric features. The importance of annealing treatments in Ar atmosphere up to 523 K was recognized, and the thermal treatment performed at 473 K for 3 h was selected as the most effective in improving the material properties. With respect to the corresponding bulk compositions, a significant enhancement in phase purity, as well as an increase in electrical conductivity and a drop in room temperature thermal conductivity, were observed in annealed films.
View Article and Find Full Text PDFWe report two new rare-earth (R) ternary intermetallic compounds-HoNiT with T = Si and Ge-that correspond to the RNiT phase earlier reported to form in Dy-Ni-T and Ho-Ni-T ternary systems. The compounds crystallize in a filled version of the orthorhombic ZrNiP-type structure with = 0.52; their stoichiometry, determined from both single-crystal and powder X-ray diffraction data, is centered on HoNiT with a narrow solid solubility range for the silicide, while the germanide appears to be a line phase.
View Article and Find Full Text PDFFilled skutterudites are currently studied as promising thermoelectric materials due to their high power factor and low thermal conductivity. The latter property, in particular, can be enhanced by adding scattering centers, such as the ones deriving from low dimensionality and the presence of interfaces. This work reports on the synthesis and characterization of thin films belonging to the Sm(FeNi)Sb-filled skutterudite system.
View Article and Find Full Text PDFThe electronic ground state of iron-based materials is unusually sensitive to electronic correlations. Among others, its delicate balance is profoundly affected by the insertion of magnetic impurities in the FeAs layers. Here, we address the effects of Fe-to-Mn substitution in the non-superconducting Sm-1111 pnictide parent compound via a comparative study of SmFe[Formula: see text]Mn[Formula: see text]AsO samples with [Formula: see text] 0.
View Article and Find Full Text PDFThe local structure of La(FeMn)AsO has been investigated using temperature dependent Fe K-edge extended x-ray absorption fine structure (EXAFS) measurements. The EXAFS data reveal distinct behavior of Fe-As and Fe-Fe atomic displacements with a clear boundary between⩽ 0.02 and> 0.
View Article and Find Full Text PDFWe investigated the U-Ni-B and Nb-Ni-B systems to search for possible new heavy fermion compounds and superconducting materials. The formation, crystal chemistry, and physical properties of UNiB and NbNiB [ternary derivatives of the cubic CrC-type (116, 3̅)] have been studied; the formation of the hypothetical "UNiB" and "NbNiB" has been disproved. UNiB [ = 10.
View Article and Find Full Text PDFThe newly discovered noncentrosymmetric superconductor ThCoC_{2} exhibits numerous types of unconventional behavior in the field dependent heat capacity data. Here we present the first measurement of the gap symmetry of ThCoC_{2} by muon spin rotation and relaxation (μSR) measurements. The temperature dependence of the magnetic penetration depth measured using the transverse field μSR experiment reveals the evidence of a nodal pairing symmetry.
View Article and Find Full Text PDFA systematic study of the physical properties and microscopic magnetism of NdPd compound, which in the paramagnetic state crystallizes in the non-centrosymmetric hexagonal ThFe-type structure (hP20-P6 mc; with a = 10.1367(1) Å and c = 6.3847(1) Å at 300 K), confirms multiple magnetic ordering transitions that occur upon cooling.
View Article and Find Full Text PDFJ Phys Condens Matter
April 2019
The goal of this work is providing a comprehensive interpretation framework for the wide and varied experimental phenomenology of the Seebeck effect in MgB samples with different levels of doping in either π or σ bands and different levels of disorder, using a combined experimental and theoretical approach. We calculate the temperature dependent diffusive Seebeck coefficient S (T) with the Boltzmann equation resolved in relaxation time approximation, taking into account the scattering with phonons and impurities, the effect of renormalization and the effect doping in a rigid band approximation. We show that selective disorder has a sizeable effect on the S magnitude, as it tunes the relative contributions of σ and π bands.
View Article and Find Full Text PDFThe substitution of Mn for Fe on the sub-lattice in LaFeAsO has a remarkable impact on both structural and magnetic properties; for example, the structural and magnetic transition temperatures decrease of ~20 K in samples with a Mn-content as low as x = 0.01. Such a dramatic effect results from the high stability of the substituting Mn ion (3d ) in its high-spin state, which opposes any variation to its electronic state (configuration), perturbing thereby interactions within the Fe sub-lattice between the Fe ions surrounding the substituent.
View Article and Find Full Text PDFWe investigate the electronic structure of a specially prepared highly dense conventional high temperature superconductor, MgB, employing high resolution photoemission spectroscopy. The spectral evolution close to the Fermi energy is commensurate to BCS descriptions as expected. However, the spectra in the wider energy range reveal the emergence of a pseudogap much above the superconducting transition temperature indicating an apparent departure from the BCS scenario.
View Article and Find Full Text PDFA new series of intermetallic compounds RAuPn (R = Y, Gd-Tm; Pn = Sb, Bi) has been discovered during the explorations of the Au-rich parts of rare-earth-containing ternary systems with p-block elements. The existence of the series is strongly restricted by both geometric and electronic factors. RAuPn compounds crystallize in the hexagonal crystal system with space group P6/m (a = 8.
View Article and Find Full Text PDFMotivated by the report of superconductivity in RTiSb (R = La and Ce) and possibly NdTiSb at ∼4 K, we grew single crystals of LaTiSb and CeTiSb by the high-temperature solution method using Sn as a flux. While in both compounds we observed a superconducting transition at 3.7 K for resistivity and low-field magnetization, our data conclusively show that it arose from residual Sn flux present in the single crystals.
View Article and Find Full Text PDFIn this Letter we report high-resolution synchrotron x-ray powder diffraction and transmission electron microscope analysis of Mn-substituted LaFeAsO samples, demonstrating that a static incommensurate modulated structure develops across the low-temperature orthorhombic phase, whose modulation wave vector depends on the Mn content. The incommensurate structural distortion is likely originating from a charge-density-wave instability, a periodic modulation of the density of conduction electrons associated with a modulation of the atomic positions. Our results add a new component in the physics of Fe-based superconductors, indicating that the density wave ordering is charge driven.
View Article and Find Full Text PDFAn investigation on the ground state magnetism of CeScSi, CeScGe (tetragonal CeScSi-type, tI12, space group I4/mmm) by temperature-dependent powder neutron diffraction has been carried out, as debated and controversial data regarding the low temperature magnetic behaviours of these two compounds were reported. Our studies reveal that, while cooling, long-range magnetic ordering in CeScSi and CeScGe takes place by a two-step process. A first transition leads to a magnetic structure with the Ce moments aligned ferromagnetically onto two neighbouring tetragonal basal a-b planes of the CeScSi-type structure; the double layers are then antiferromagnetically coupled to each other along the c-axis.
View Article and Find Full Text PDFThe crystal chemical features of the new series of compounds R6Mg23C with R = La-Sm or Gd and Ce6Mg23Z with Z = C, Si, Ge, Sn, Pb, P, As, or Sb have been studied by means of single-crystal and powder X-ray diffraction techniques. All phases crystallize with the cubic Zr6Zn23Si prototype (cF120, space group Fm3̅m, Z = 4), a filled variant of the Th6Mn23 structure. While no Th6Mn23-type binary rare earth-magnesium compound is known to exist, the addition of a third element Z (only 3 atom %), located into the octahedral cavity of the Th6Mn23 cell (Wyckoff site 4a), stabilizes this structural arrangement and makes possible the formation of the ternary R6Mg23Z compounds.
View Article and Find Full Text PDFThe magnetic properties and magnetic structures of the R 5Ni2In4 and the microfibrous R 11Ni4In9 compounds with R = Tb and Ho have been examined using magnetization, heat capacity, and neutron diffraction data. Rare earth atoms occupy three and five symmetrically inequivalent rare earth sites in R 5Ni2In4 and R 11Ni4In9 compounds, respectively. As a result of the intra- and inter-magnetic sublattice interactions, the magnetic exchange interactions are different for various rare earth sites; this leads to a cascade of magnetic transitions with a strong hierarchy in the temperature dependence of the magnetic orderings.
View Article and Find Full Text PDFThe synthesis of the new equiatomic RScSb (R = La-Nd, Sm, Gd-Tm, Lu, Y) compounds has been recently reported. These rare earth compounds crystallize in two different crystal structures, adopting the CeScSi-type (I4/mmm) for the lighter R (La-Nd, Sm) and the CeFeSi-type (P4/nmm) structure for the heavier R (R = Gd-Tm, Lu, Y). Here we report the results of neutron diffraction, magnetization and heat capacity measurements on some of these compounds (R = Ce, Pr, Nd, Gd and Tb).
View Article and Find Full Text PDFSingle crystals of the quaternary europium compounds EuRhAl4Si2 and EuIrAl4Si2 were synthesized by using the Al-Si binary eutectic as a flux. The structure of the two quaternary compounds has been refined by single crystal X-ray diffraction. Both compounds are stoichiometric and adopt an ordered derivative of the ternary KCu4S3 structure type (tetragonal tP8, P4/mmm).
View Article and Find Full Text PDFJ Phys Condens Matter
July 2011
The synthesis of the new compounds R(15)Si(9)C with R = Sm, Gd-Er, Y and R(15)Ge(9)C with R = Ce, Pr and Nd has been recently reported; these compounds crystallize in the hexagonal La(15)Ge(9)Fe structure type, hP50-P6(3)mc, Z = 2 (ordered superstructure of La(5)Ge(3) (Mn(5)Si(3)-type, hP 16-P6(3)/mcm, Z = 2)). Here we report the results of a neutron diffraction investigation that we have performed to study the crystal and magnetic structures of the R(15)Si(9)C compounds with R = Tb, Ho and Er. All three compounds see the establishment of commensurate magnetic order with a predominantly ferromagnetic interaction.
View Article and Find Full Text PDFThe structural and magnetic properties of Yb(2)Al(1-x)Mg(x)Si(2) (x = 0, 0.5 and 1), crystallizing in the tetragonal Mo(2)FeB(2)-type structure, are reported in this work. Yb(2)AlSi(2) exhibits a Pauli paramagnetic ground state arising due to spin/valence fluctuations induced by a significant Yb 4f conduction band hybridization.
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