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The single-band, quasi-two dimensional metals PdCoO2 and PtCoO2 have recently come to prominence because of their extremely long mean free paths, which establish them as some of the most electronically pure materials known, and as potential hosts of previously unobservable regimes of electronic transport. To fully establish their magnetotransport properties, we have studied the magnetoresistance and Hall effect in bulk single crystals to which electrical contacts have been made with high precision using focused ion beam machining. We observe a strong temperature dependence of the Hall resistivity in small applied fields, linked to a large violation of Kohler's rule in the magnetoresistance. We discuss the extent to which these observations can be accounted for by standard transport theory. Quantum transport: benchmarks A magneto-transport experiment on ultra-pure PdCoO2 and PtCoO2 establishes a baseline for comparison to more exotic materials. An international team lead by Nabhanila Nandy and Andrew Mackenzie from the Max Planck Institute for Chemical Physics of Solids have carefully analysed the magneto-resistance of these materials and compared to standard theoretical descriptions. They find a strong temperature dependence, which reveals that more than one microscopic length scale is controlling the electron scattering. The Drude transport theory cannot account for this, and explaining it within Boltzmann theory requires some assumptions that need further theoretical support. Given the recent interest in exotic quantum transport–such as hydrodynamic electron flow or the very low resistivity measured in Dirac and Weyl semimetals–these results provide a reference for future work. [ABSTRACT FROM AUTHOR]

Abstract: Bi2CuO4 is a spin 1/2 model compound with ferromagnetically (FM) ordered chains that are antiferromagnetically (AFM) arranged with respect to each other. To investigate the microscopic origin of this unusual magnetic structure, we performed DFT calculations to evaluate the relevant orbitals and couplings. Total energy calculations yield a magnetic ground state in agreement with the experimental data. Based on a tight-binding fit we estimated the leading exchange integrals. The main coupling arises between the chains, while the in-chain interaction is relatively small. The FM arrangement of chains is due to strong AFM exchange of neighbouring CuO4 units of the different chains. [Copyright &y& Elsevier]

The concerted experimental and computational study reports on the polymorphic behavior of RuBr3. Highly‐resolved X‐ray powder diffraction measurements of the modification lt‐RuBr3 give direct evidence for peak splitting substantiating an orthorhombic unit cell with additional weak intensities confirming a primitive lattice. The crystal structure of lt‐RuBr3 is determined using the intensities of a "Drilling" individuum. For lt‐RuBr3, findings of density functional theory calculations suggest that the deviation from hexagonal symmetry is mainly driven by electronic correlations. Reinvestigation of the recently reported high‐pressure modification hp‐RuBr3 essentially confirms the rhombohedral BiI3‐type crystal structure (space group R3‾ ${\bar{3}}$). Simulations of the atomic arrangement of hp‐RuBr3 indicate that spin‐orbit coupling and corrections for the van‐der‐Waals dispersive forces are mandatory to reach a reasonable agreement with the experimentally determined crystal structure. [ABSTRACT FROM AUTHOR]

The layered delafossite metal PdCrO2 is a natural heterostructure of highly conductive Pd layers Kondo coupled to localized spins in the adjacent Mott insulating CrO2 layers. At high temperatures, T, it has a T-linear resistivity which is not seen in the isostructural but nonmagnetic PdCoO2. The strength of the Kondo coupling is known, as-grown crystals are extremely high purity and the Fermi surface is both very simple and experimentally known. It is therefore an ideal material platform in which to investigate “Planckian metal” physics. We do this by means of controlled introduction of point disorder, measurement of the thermal conductivity and Lorenz ratio, and studying the sources of its high-temperature entropy. The T-linear resistivity is seen to be due mainly to elastic scattering and to arise from a sum of several scattering mechanisms. Remarkably, this sum leads to a scattering rate within 10% of the Planckian value of kBT/ℏ. [ABSTRACT FROM AUTHOR]

Lanthanoide sulfide iodides LnSI with Ln: Gd-Lu are prepared by solid state reaction of an equimolar mixture of Ln, S and I (fused silica tube, 900 °C, 10 d) and powder XRD cell parameters are given. [ABSTRACT FROM AUTHOR]

Since the discovery of the Fe-based superconductors (FeSC) a lot of efforts has been applied to elucidate the microscopic mechanism behind cooper pairing and the symmetry of the order parameter. Examination of effective interactions of electrons with spin-fluctuations in these systems yield that couplings are not weak and the materials have to be considered in a strong coupling scheme. In the present article, we review some aspects of the description of iron-based superconductors in the frame of the Eliashberg approach for multiband systems. The application of the Eliashberg scheme is demonstrated with two compounds Ba0.6K0.4Fe2As2 and Ca0.32Na0.68Fe2As2. In both cases, it was found that these materials are in the intermediate coupling regime. Further, we consider effects of impurities on physical properties of multiband superconductors. It is demonstrated that the impurities affect nontrivially the superconducting properties. In particular, they may trigger a symmetry change of superconducting order parameters. This effect can be used for determination of the superconducting order parameter. Finally, we consider KFe2As2 and show that its thermodynamic properties are consistent with a nodal superconducting order parameter. [ABSTRACT FROM AUTHOR]

We discuss the temperature (T ) dependence of the generalized density of states G(ω,T ) and of the phonon intensities of the filled skutterudite compound YbFe4Sb12 investigated by inelastic neutron scattering in an extensive range of energy-momentum phase space. The inelastic response has been measured at T =1.7, 50, 100, 200, and 290 K at a thermal time-of-flight spectrometer with an incident wavelength of 1.3 Å. The experimentally determined signal is compared with T -dependent ab initio powder averaged lattice dynamics calculations. An additional set of T -dependent spectra is calculated with thermal displacement parameters extracted from neutron diffraction data within the incoherent approximation. G(ω,T ) shows a nonuniform intensity variation with T due to the specific thermal displacement parameters of Yb, Fe, and Sb. We demonstrate that this temperature variation can be well reproduced by the two simulation approaches. In particular, the ab initio powder averaged lattice dynamics calculation is capable of reproducing the momentum and energy characteristics of the phonon form factors of YbFe4Sb12. [ABSTRACT FROM AUTHOR]

A microscopic magnetic model of the low-pressure modification of CdVO3 is established, based on density functional theory (DFT) band-structure calculations, magnetization measurements, and quantum Monte Carlo simulations. This compound is a rare example of a quasi-one-dimensional spin- 1/2 system showing exclusively ferromagnetic exchange. The spin lattice of CdVO3 entails zigzag chains with an effective intrachain coupling J ≃ -90 K and interchain couplings of Jc ≃ - 18 K and Ja ≃ -3 K. Quantum fluctuations are partially suppressed by the sizable interchain coupling Jc that leads to an intermediate regime between one-dimensional and two-dimensional ferromagnetic systems. Apart from the peculiar spin model, CdVO3 features an unusual mechanism of ferromagnetic superexchange. The couplings largely originate from Cd 5s states mediating hoppings between half-filled and empty 3d states of V+4. [ABSTRACT FROM AUTHOR]

The vibrational dynamics of the ternary Ca1-xFe4Sb12, Ba1-xFe4Sb12, Sr1-xFe4Sb12, and Yb1-xFe4Sb12 compounds is studied for its temperature dependence, dispersion relations, and material properties by experiments and ab initio powder-averaged lattice-dynamics (PALD) calculations. The experimental techniques used are high-resolution inelastic neutron scattering (INS) and inelastic x-ray scattering (IXS). Vibrational properties of polycrystalline material have been mapped out in an extensive energy-momentum phase space facilitating the study of powder-averaged phonon-dispersion relations within the first and second Brillouin zones. Qualitatively, the experimental dynamic structure factor S(Q,ω) matches, to a high degree, PALD calculations allowing different schemes of collective vibrational eigenmodes to be evaluated. From the PALD calculations, quantitative values of velocity of sound, Debye temperatures, and elastic, bulk, and Young's moduli are computed. The variation of the generalized density of states G(ω) with temperature is studied experimentally in the range from 2 to 600 K. No particular anomalies in the collective dynamics are observed apart from a global softening of G(ω) upon heating. [ABSTRACT FROM AUTHOR]

We report a systematic study of the influence of antiferromagnetic and ferromagnetic phases of Eu2+ moments on the superconducting phase upon doping the As site by isovalent P, which essentially acts like chemical pressure on EuFe2As2. Bulk superconductivity with transition temperatures of 22 and 28 K are observed for x=0.16 and 0.20 samples, respectively. The Eu ions order antiferromagnetically for x ≤ 0.13, while bulk superconductivity coexists with Eu-antiferromagnetism for 0.13 < x<0.22. In contrast, a crossover is observed for x≥0.22 whereupon the Eu ions order ferromagnetically and superconductivity is fully suppressed. Density-functional-theory-based calculations reproduce the observed experimental findings consistently. We discuss in detail the coexistence of superconductivity and magnetism in a tiny region of the phase space and comment on the competition of ferromagnetism and superconductivity in the title compound. [ABSTRACT FROM AUTHOR]

The interplay between spin–orbit coupling and structural inversion symmetry breaking in solids has generated much interest due to the nontrivial spin and magnetic textures which can result. Such studies are typically focused on systems where large atomic number elements lead to strong spin–orbit coupling, in turn rendering electronic correlations weak. In contrast, here we investigate the temperature-dependent electronic structure of Ca3Ru2O7, a 4d oxide metal for which both correlations and spin–orbit coupling are pronounced and in which octahedral tilts and rotations combine to mediate both global and local inversion symmetry-breaking polar distortions. Our angle-resolved photoemission measurements reveal the destruction of a large hole-like Fermi surface upon cooling through a coupled structural and spinreorientation transition at 48 K, accompanied by a sudden onset of quasiparticle coherence. We demonstrate how these result from band hybridization mediated by a hidden Rashba-type spin– orbit coupling. This is enabled by the bulk structural distortions and unlocked when the spin reorients perpendicular to the local symmetry-breaking potential at the Ru sites. We argue that the electronic energy gain associated with the band hybridization is actually the key driver for the phase transition, reflecting a delicate interplay between spin–orbit coupling and strong electronic correlations and revealing a route to control magnetic ordering in solids. [ABSTRACT FROM AUTHOR]

A detailed experimental investigation of Fe1+yTe (y = 0.11, 0.12) using pulsed magnetic fields up to 60 T confirms remarkable magnetic shape-memory (MSM) effects. These effects result from magnetoelastic transformation processes in the low-temperature antiferromagnetic state of these materials. The observation of modulated and finely twinned microstructure at the nanoscale through scanning tunneling microscopy establishes a behavior similar to that of thermoelastic martensite. We identified the observed, elegant hierarchical twinning pattern of monoclinic crystallographic domains as an ideal realization of crossing twin bands. The antiferromagnetism of the monoclinic ground state allows for a magnetic-field–induced reorientation of these twin variants by the motion of one type of twin boundaries. At sufficiently high magnetic fields, we observed a second isothermal transformation process with large hysteresis for different directions of applied field. This gives rise to a second MSM effect caused by a phase transition back to the field-polarized tetragonal lattice state. [ABSTRACT FROM AUTHOR]

The ability to modulate the collective properties of correlated electron systems at their interfaces and surfaces underpins the burgeoning field of "designer" quantum materials. Here, we show how an electronic reconstruction driven by surface polarity mediates a Stoner-like magnetic instability to itinerant ferromagnetism at the Pd-terminated surface of the nonmagnetic delafossite oxide metal PdCoO2. Combining angle-resolved photoemission spectroscopy and density-functional theory calculations, we show how this leads to a rich multiband surface electronic structure. We find similar surface state dispersions in PdCrO2, suggesting surface ferromagnetism persists in this sister compound despite its bulk antiferromagnetic order. [ABSTRACT FROM AUTHOR]

Despite the fact that the Fe-based superconductors (FeSCs) were discovered nearly 10 years ago, the community is still devoting a tremendous effort toward elucidating their relevant microscopic pairing mechanism(s) and interactions. At present, there is still no consistent interpretation of their normal state properties, where the strength of the electron–electron interaction and the role of correlation effects are under debate. Here, we examine several common materials and illustrate various problems and concepts that are generic for all FeSCs. Based on empirical observations and qualitative insight from density functional theory, we show that the superconducting and low-energy thermodynamic properties of the FeSCs can be described semi-quantitively within multiband Eliashberg theory. We account for the important high-energy mass renormalizations phenomenologically, and in agreement with constraints provided by thermodynamic, optical, and angle-resolved photoemission data. When seen in this way, many representative FeSCs with Tc < 40 K studied so far are found to belong to an intermediate coupling regime (with the possible exception of some systems near a quantum critical point or in the vicinity of a Lifshitz transition). This finding is in contrast to the generally strong coupling scenarios proposed in the early period of the FeSC history. We also discuss several related issues, including the role of band shifts as measured by the positions of van Hove singularities, and the nature of a recently suggested quantum critical point in the strongly hole-doped systems AFe2As2 (A = K, Rb, Cs). Using high-precision full relativistic GGA-band structure calculations, we arrive at a somewhat milder mass renormalization in comparison with previous studies. From the calculated mass anisotropies of all Fermi surface sheets, only the ε-pocket near the corner of the BZ is compatible with the experimentally observed anisotropy of the upper critical field, pointing to its dominant role in the superconductivity of these three compounds. [ABSTRACT FROM AUTHOR]

Two new ternary borides TM7Fe3B8 (TM = Nb, Ta) were synthesized by high-temperature thermal treatment of samples obtained by arc-melting. This new type of structure with space group P6/mmm, comprises TM slabs containing isolated planar hexagonal [B6] rings and iron centered TM columns in a Kagome type of arrangement. Chemical bonding analysis in Nb7Fe3B8 by means of the electron localizability approach reveals two-center interactions forming the Kagome net of Fe and embedded B, while weaker multicenter bonding present between this net and Nb atoms. Magnetic susceptibility measurements reveal antiferromagnetic order below TN = 240 K for Nb7Fe3B8 and TN = 265 K for Ta7Fe3B8. Small remnant magnetization below 0.01μB per f.u. is observed in the antiferromagnetic state. The bulk nature of the magnetic transistions was confirmed by the hyperfine splitting of the Mössbauer spectra, the sizable anomalies in the specific heat capacity, and the kinks in the resistivity curves. The high-field paramagnetic susceptibilities fitted by the Curie–Weiss law show effective paramagnetic moments μeff≈ 3.1μB/Fe in both compounds. The temperature dependence of the electrical resistivity also reveals metallic character of both compounds. Density functional calculations corroborate the metallic behaviour of both compounds and demonstrate the formation of a sizable local magnetic moment on the Fe-sites. They indicate the presence of both antiferro- and ferrromagnetic interactions. [ABSTRACT FROM AUTHOR]

The thermoelectric properties of single-crystalline and polycrystalline FeGa3 are systematically investigated over a wide temperature range. At low temperatures, below 20 K, previously not known pronounced peaks in the thermal conductivity (400-800 W K-1 m-1) with corresponding maxima in the thermopower (in the order of -16000 μV K-1) were found in single-crystalline samples. Measurements in single crystals along [100] and [001] directions indicate only a slight anisotropy in both the electrical and thermal transports. From susceptibility and heat-capacity measurements, a magnetic or structural phase transition was excluded. Using density functional theory based calculations, we have revisited the electronic structure of FeGa3 and compared the magnetic (including correlations) and nonmagnetic electronic densities of states. Thermopower at fixed carrier concentrations is calculated using semiclassical Boltzmann transport theory, and the calculated results match fairly with our experimental data. The inclusion of strong electron correlations treated in a mean field manner (by LSDA + U) does not improve this comparison, rendering strong correlations as the sole explanation for the low-temperature enhancement unlikely. Eventually, after a careful review, we assign the peaks in the thermopower as a manifestation of the phonon-drag effect, which is supported by thermopower measurements in a magnetic field. [ABSTRACT FROM AUTHOR]

A combined theoretical and experimental study of the natural Cu2+mineral callaghanite is presented. Its crystal structure features well separated Cu2(OH)6 structural dimers with weakly bonded carbonate groups and water molecules in between. Susceptibility, field-dependent magnetization and specific-heat measurements reveal a compound with a small spin gap of about 7 K. The observed magnetic properties are well described by a model of isolated antiferromagnetic spin dimers. Possible ferromagnetic interactions between the dimers amount to -1.5 K, at most. Different flavors of electronic structure calculations have been employed to locate the magnetic dimers in the crystal structure, i.e., to determine whether they coincide with the structural dimers or not. Calculations of the coupling between the structural dimers clearly show that magnetic and structural dimers are the same. For the intradimer coupling, however, the computational results confirmed a coupling strength close to zero but the sign of the coupling could not be determined unambiguously. Based on this finding, we then discuss how the reliability of the numerical methods depends on the characteristics of exchange pathways and on structural features of the compound in general. Eventually, we try to provide a minimum coupling strength that is needed for a reliable computational description. [ABSTRACT FROM AUTHOR]

We present a detailed investigation of the electronic phase diagram of effectively charge compensated Ba1-xKx(Fe1-yCoy)2As2 with x/2 ≈ y. Our experimental study by means of x-ray diffraction, Mössbauer spectroscopy, muon spin relaxation and ac-susceptibility measurements on polycrystalline samples is complemented by density functional electronic structure calculations. For low substitution levels of x/2 ≈ y ⩽ 0.13, the system displays an orthorhombically distorted and antiferromagnetically ordered ground state. The low-temperature structural and magnetic order parameters are successively reduced with increasing substitution level. We observe a linear relationship between the structural and the magnetic order parameter as a function of temperature and substitution level for x/2 ≈ y ⩽ 0.13. At intermediate substitution levels in the range between 0.13 and 0.19, we find superconductivity with a maximum Tc of 15 K coexisting with static magnetic order on a microscopic length scale. For higher substitution levels x/2 ≈ y ⩾ 0.25, a tetragonal nonmagnetic ground state is observed. Our DFT calculations yield a significant reduction of the Fe 3d density of states at the Fermi energy and a strong suppression of the ordered magnetic moment in excellent agreement with experimental results. The appearance of superconductivity within the antiferromagnetic state can by explained by the introduction of disorder due to nonmagnetic impurities to a system with a constant charge carrier density. [ABSTRACT FROM AUTHOR]

Durch dimensionales Einschränken von kristallinen Schichten während eines nichtepitaxialen Verwachsungsprozesses werden Nanokristall ‐ Ensembles mit genau einstellbarer Größe erhalten. Synchrotron ‐ Röntgenbeugung, Elektronenmikroskopie und Dichtefunktionalrechnungen zufolge ermöglicht es ein größeninduzierter struktureller Phasenübergang zweiter Ordnung, die Kristallstruktur eines schichtförmigen Halbleiters (SnSe) über die Dicke der einzelnen Schichten kontinuierlich zu verändern. [ABSTRACT FROM AUTHOR]

By dimensionally constraining crystalline layers in a non‐epitaxial intergrowth, nanocrystal ensembles with well‐defined and precisely controlled size are prepared. Synchrotron X‐ray diffraction, electron microscopy, and density functional theory show that a size‐induced second‐order structural transition allows the crystal structure of a layered semiconductor (SnSe) to be continuously tuned by controlling the thickness of the individual layers. [ABSTRACT FROM AUTHOR]

We report on the microscopic magnetic modeling of the spin-1/2 copper mineral malachite at ambient and elevated pressures. Despite the layered crystal structure of this mineral, the ambient-pressure susceptibility and magnetization data can be well described by an unfrustrated quasi-one-dimensional magnetic model. Weakly interacting antiferromagnetic alternating spin chains are responsible for a large spin gap of 120 K. Although the intradimer Cu-O-Cu bridging angles are considerably smaller than the interdimer angles, density functional theory (DFT) calculations revealed that the largest exchange coupling of 190 K operates within the structural dimers. The lack of the inversion symmetry in the exchange pathways gives rise to sizable Dzyaloshinskii-Moriya interactions which were estimated by full-relativistic DFT+U calculations. Based on available high-pressure crystal structures, we investigate the exchange couplings under pressure and make predictions for the evolution of the spin gap. The calculations evidence that intradimer couplings are strongly pressure dependent and their evolution underlies the decrease of the spin gap under pressure. Finally, we assess the accuracy of hydrogen positions determined by structural relaxation within DFT and put forward this computational method as a viable alternative to elaborate experiments [ABSTRACT FROM AUTHOR]

Magnetic susceptibility measurements and a microscopic magnetic model of the mineral clinoclase Cu3(AsO4)(OH)3 are reported. This spin-1/2 material can be well described as a combination of two nonequivalent spin dimers with the sizable magnetic couplings of J≃700 K and JD2≃300 K but only small interdimer couplings. Based on density functional theory calculations, we pinpoint the location of dimers in the rather complex crystal structure. Counterintuitively, the largest exchange coupling operates between the structural Cu2O6 dimers. Additionally, we investigate magnetostructural correlations in Cu2O6 structural dimers by considering the influence of the hydrogen position on the magnetic coupling. To evaluate accurate exchange couplings, we establish the hydrogen positions that were not known so far and analyze the pattern of hydrogen bonding. [ABSTRACT FROM AUTHOR]

We report on the quasi-two-dimensional magnetism of the natural mineral diaboleite Pb2Cu(OH)4Cl2 with a tetragonal crystal structure, which is closely related to that of the frustrated spin-½ magnet PbVO3. Magnetic susceptibility of diaboleite is well described by a Heisenberg spin model on a diluted square lattice with the nearest-neighbor exchange of J ≃ 35 K and about 5% of nonmagnetic impurities. The dilution of the spin lattice reflects the formation of Cu vacancies that are tolerated by the crystal structure of diaboleite. The weak coupling between the magnetic planes triggers the long-range antiferromagnetic order below TN ≃ 11 K. No evidence of magnetic frustration is found. We also analyze the signatures of the long-range order in heat-capacity data, and discuss the capability of identifying magnetic transitions with heat-capacity measurements. [ABSTRACT FROM AUTHOR]

We apply neutron diffraction, high-resolution synchrotron x-ray diffraction, magnetization measurements, electronic structure calculations, and quantum Monte-Carlo simulations to unravel the structure and magnetism of (CuCl)LaTa²O7. Despite the pseudo-tetragonal crystallographic unit cell, this compound features an orthorhombic superstructure, similar to the Nb-containing (CuX)LaNb²O7 with X = CI and Br. The spin lattice entails dimers formed by the antiferromagnetic fourth-neighbor coupling J4, as well as a large number of nonequivalent interdimer couplings quantified by an effective exchange parameter Jeff. In (CuCl)LaTa²O7, the interdimer couplings are sufficiently strong to induce the long-range magnetic order with the Néel temperature TN ≃ 7 K and the ordered magnetic moment of 0.53μB, as measured with neutron diffraction. This magnetic behavior can be accounted for by Jeff/J4 ≃ 1.6 and J4 ≃ 1.6 K. We further propose a general magnetic phase diagram for the (CuCl)LaNb²O7-type compounds, and explain the transition from the gapped spin-singlet (dimer) ground state in (CuCl)LaNb²O7 to the long-range antiferromagnetic order in (CuCl)LaTa²O7 and (CuBr)LaNb²O7 by an increase in the magnitude of the interdimer couplings Jeff/J4, with the (CuCl)LaM²O7 (M = Nb, Ta) compounds lying on different sides of the quantum critical point that separates the singlet and long-range-ordered magnetic ground states. [ABSTRACT FROM AUTHOR]

We report on a comprehensive experimental and theoretical study of the quasi-one-dimensional quantum magnet CuNCN. Based on magnetization measurements above room temperature, as well as muon spin rotation and electron spin resonance measurements, we unequivocally establish the localized Cu+2-based magnetism and the magnetic transition around 70 K, both controversially discussed in the previous literature. Thermodynamic data conform to the uniform-spin-chain model with a nearest-neighbor intrachain coupling of about 2300 K, in remarkable agreement with the microscopic magnetic model based on density functional theory band-structure calculations. Using exact diagonalization and the coupled-cluster method we derive a collinear antiferromagnetic order with a strongly reduced ordered moment of about 0.4&mgr;B, indicating strong quantum fluctuations inherent to this quasi-one-dimensional spin system. We reanalyze the available neutron-scattering data, and conclude that they are not sufficient to resolve or disprove the magnetic order in CuNCN. By contrast, spectroscopic techniques indeed show signatures of long-range magnetic order below 70 K, yet with a rather broad distribution of internal field probed by implanted muons. We contemplate the possible structural origin of this effect and emphasize the strong anisotropic reflection broadening observed with synchrotron powder x-ray diffraction on stoichiometric samples of CuNCN, as well as possible deviations from the ideal CuNCN stoichiometry. [ABSTRACT FROM AUTHOR]

We present a comprehensive study of the crystal structure, magnetic structure, and microscopic magnetic model of (CuCl)LaNb2O7. the Br analog of the spin-gap quantum magnet (CuCl)LaNb2O7. Despite similar crystal structures and spin lattices, the magnetic behavior and even peculiarities of the atomic arrangement in the Cl and Br compounds are very different. The high-resolution x-ray and neutron data reveal a split position of Br atoms in (CuBr)LaNb207. This splitting originates from two possible configurations developed by [CuBr] zigzag ribbons. While the Br atoms are locally ordered in the ab plane, their arrangement along the c direction remains partially disordered. The predominant and energetically more favorable configuration features an additional doubling of the c lattice parameter that was not observed in (CuCl)LaNb207. (CuBr)LaNb207 undergoes long-range antiferromagnetic ordering at TN = 32 K, which is nearly 70% of the leading exchange coupling J4 ≃ 48 K. The Br compound does not show any experimental signatures of low-dimensional magnetism because the underlying spin lattice is three-dimensional. The coupling along the c direction is comparable to the couplings in the ab plane, even though the shortest Cu-Cu distance along c (11.69 &Adeg;) is threetimes larger than nearest-neighbor distances in the ab plane (3.55 &Adeg;). The stripe antiferromagnetic long-range order featuring columns of parallel spins in the ab plane and antiparallel spins along c is verified experimentally and confirmed by the microscopic analysis. [ABSTRACT FROM AUTHOR]

Recently, we reported [M. Wagner et al., J. Mater. Res. 26, 1886 (2011)] transport measurements on the semiconducting intermetallic system Ruln3 and its substitution derivatives RuIn3-xAx (A = Sn, Zn). Higher values of the thermoelectric figure of merit (zT = 0.45) compared to the parent compound were achieved by chemical substitution. Here, using density functional theory based calculations, we report on the microscopic picture behind the measured phenomenon. We show in detail that the electronic structure of the substitution variants of the intermetallic system Ruln3-xAx (A = Sn, Zn) changes in a rigid-band-like fashion. This behavior makes possible the fine tuning of the substitution concentration to take advantage of the sharp peaklike features in the density of states of the semiconducting parent compound. Trends in the transport properties calculated using the semiclassical Boltzmann transport equations within the constant scattering time approximation are in good agreement with the former experimental results for Ruin3-xSnx. Based on the calculated thermopower for the &rgr;-doped systems, we reinvestigated the Zn-substituted derivative and obtained ZnO-free RuIn3-xZnx. The new experimental results are consistent with the calculated trend in thermopower and yield a large zT value of 0.8. [ABSTRACT FROM AUTHOR]