Antiferromagnetic Correlations in Strongly Valence Fluctuating CeIrSn.

CeIrSn with a quasikagome Ce lattice in the hexagonal basal plane is a strongly valence fluctuating compound, as we confirm by hard x-ray photoelectron spectroscopy and inelastic neutron scattering, with a high Kondo temperature of T_{K}∼480 K. We report a negative in-plane thermal expansion α/T below 2 K, which passes through a broad minimum near 0.75 K. Volume and a-axis magnetostriction for B∥a are markedly negative at low fields and change sign before a sharp metamagnetic anomaly at 6 T. These behaviors are unexpected for Ce-based intermediate valence systems, which should feature positive expansivity. Rather they point towards antiferromagnetic correlations at very low temperatures. This is supported by muon spin relaxation measurements down to 0.1 K, which provide microscopic evidence for a broad distribution of internal magnetic fields. Comparison with isostructural CeRhSn suggests that these antiferromagnetic correlations emerging at T≪T_{K} result from geometrical frustration.

Effects of Y- and La-doping on the magnetic ordering, Kondo effect, and spin dynamics in Ce1-xMxRu2Al10.

The influence of Y- and La-substitution for Ce on the competing Kondo effect and magnetic ordering, as well as on spin dynamics in the Kondo semiconductor CeRu2Al10have been investigated by means of thermal, electronic, and magnetic properties. The parent compound CeRu2Al10is known to be a controversial antiferromagnet with high magnetic ordering temperatureT0= 27 K. A small negative chemical pressure caused by La-doping results rapid suppression ofT0and spin gap energy Δm, compared to a small positive pressure caused by Y-doping. Upon Y- and La-doping, the electrical resistivityρ(T) illustrates the evolution from dense Kondo semiconductor to incoherent single-ion Kondo behaviour, and hence weakens thec-fhybridization and thus lowers the Kondo temperature. The 5% Y- and La-doped compounds show enormous enhancement in the thermoelectric power and complex behaviour in the Hall resistivity belowT0due to an abrupt change in charge carrier mobility with temperature. The magnetic contribution to electrical resistivityρmag(T) (≳50% La) and specific heatCP(T)/T(≳70% La) evidence non-Fermi-liquid behaviour at low temperature in the La-doped system, due to interplay of atomic disorder with spin-fluctuation. Application of magnetic field suppresses the spin-fluctuation inCP(T)/Tand eventually emerges to Fermi-liquid state in the 95% La-doped compound in 9 T. The magnetic phase diagram illustrates that the strength of the Kondo interaction in the doped systems are primarily controlled by the effect of volume change as described by the compressible Kondo lattice model. We ascribe the fascinating observation ofTK≃ 4T0to anisotropy in the single-ion crystal electric field in the presence of strong anisotropicc-fhybridization.

[A German version of the Cambridge examination for mental disorders of older people with Down's syndrome and others with intellectual disabilities : A diagnostic procedure for detecting dementia in people with Down's syndrome]. / Eine deutsche Fassung der Cambridge Examination for Mental Disorders of Older People with Down's Syndrome and Others with Intellectual Disabilities : Ein Diagnoseverfahren zur Erfassung von Demenz bei Menschen mit einem Down-Syndrom.

BACKGROUND: Although people with Down's syndrome (DS) are at a high risk of developing an Alzheimer type dementia (AD) due to a triplication of the amyloid precursor gene, there are practically no internationally available test procedures to detect cognitive deficits in this at risk population in the German language. OBJECTIVE: The aim was to provide a German translation and intercultural adaptation of the Cambridge examination for mental disorders of older people with Down's syndrome and others with intellectual disabilities (CAMDEX-DS), which is available in English and Spanish. This instrument for diagnostics and monitoring consists of a psychological test examination (CAMCOG-DS) and a caregiver interview. METHODS: The translation and adaptation of the CAMDEX-DS were achieved through a multistep translation process, whereby two independent forward and back translations were provided by professional translators and a consensus version was finalized and tested. The final version of the caregiver interview was applied to 11 subjects and the CAMCOG-DS was conducted with 28 patients. RESULTS: The German version of the CAMDEX-DS proved to be easily administered. The CAMCOG-DS could be fully administered to 21 out of 28 patients (75%). The CAMCOG-DS values were much lower for older patients aged ≥45 years than for younger patients (46/109 vs. 73.5/109; p = 0.033). DISCUSSION: The German version of the CAMDEX-DS provides an internationally recognized tool for the diagnostics and monitoring of cognitive decline in Down's syndrome. Furthermore, the German version can standardize medical care of these patients. In particular it provides a means of participation in international research trials for this at risk population.

Crystal structure and physical properties of the two stannides EuPdSn2 and YbPdSn2.

We report on synthesis, crystal structure and physical properties of the isotypic compounds YbPdSn2 and EuPdSn2 crystallizing in the MgCuAl2-type structure. In both stannides a divalent state of respective rare earth element was found from analysis of the magnetic susceptibilities. Whereas in YbPdSn2 only weak paramagnetic behaviour is observed, in EuPdSn2 a long-range magnetic phase transition occurs at 12.5 K with complex magnetic behaviour evidenced by magnetic susceptibity and specific heat measurements. Under the influence of magnetic field, the magnetic behaviour was found to evolve from an antiferromagnetic to a ferromagnetic state as a consequence of a re-arrangement of magnetic moments.

Magnetic structure and field-dependent magnetic phase diagram of Ni2In-type PrCuSi.

The magnetic structure of the ternary equiatomic intermetallic compound PrCuSi is investigated using neutron powder diffraction experiments in 0 T as well as in external magnetic fields up to 2 T. The PrCuSi compound crystallizes in the hexagonal Ni2In-type structure, in the space group P63/mmc. In this structure, cationic ordering of Cu and Si takes place. The antiferromagnetic phase transition in the Pr sublattice takes place at [Formula: see text] K in 0 T. Under an external magnetic field of 2 T, a field-induced ferromagnetic phase is observed. Magnetoelastic coupling is evidenced by an increase in the unit cell volume. Clear signatures of a mixed antiferromagnetic and ferromagnetic phase in weak, intermediate fields, 0.4-0.8 T, are obtained from the present study. Using the present set of experimental data, we construct the H - T phase diagram of PrCuSi.

Absence of a long-range ordered magnetic ground state in Pr3Rh4Sn13 studied through specific heat and inelastic neutron scattering.

Signatures of absence of a long-range ordered magnetic ground state down to 0.36 K are observed in magnetic susceptibility, specific heat, thermal/electrical transport and inelastic neutron scattering data of the quasi-skutterudite compound Pr3Rh4Sn13 which crystallizes in the Yb3Rh4Sn13-type structure with a cage-like network of Sn atoms. In this structure, Pr3+ occupies a lattice site with D 2d point symmetry having a ninefold degeneracy corresponding to J = 4. The magnetic susceptibility of Pr3Rh4Sn13 shows only a weak temperature dependence below 10 K; otherwise remaining paramagnetic-like in the range, 10 K-300 K. From the inelastic neutron scattering intensity of Pr3Rh4Sn13 recorded at different temperatures, we identify excitations at 4.5(7) K, 5.42(6) K, 10.77(5) K, 27.27(5) K, 192.28(4) K and 308.33(3) K through a careful peak analysis. However, no signatures of long-range magnetic order are observed in the neutron data down to 1.5 K, which is also confirmed by the specific heat data down to 0.36 K. A broad Schottky-like peak is recovered for the magnetic part of the specific heat, C 4f, which suggests the role of crystal electric fields of Pr3+ . A crystalline electric field model consisting of 7 levels was applied to C 4f which leads to the estimation of energy levels at 4.48(2) K, 6.94(4) K, 11.23(8) K, 27.01(5) K, 193.12(6) K and 367.30(2) K. The CEF energy levels estimated from the heat capacity analysis are in close agreement with the excitation energies seen in the neutron data. The Sommerfeld coefficient estimated from the analysis of magnetic specific heat is [Formula: see text] mJ K-2 mol-Pr which suggests the formation of heavy itinerant quasi-particles in Pr3Rh4Sn13. Combining inelastic neutron scattering results, analysis of the specific heat data down to 0.36 K, magnetic susceptibility and, electrical and thermal transport, we establish the absence of long-range ordered magnetic ground state in Pr3Rh4Sn13.

A new ternary magnetically ordered heavy fermion compound Pr2Rh3Ge: magnetic, electronic and thermodynamic properties.

The results of the magnetic, electron transport, heat capacity and heat conduction measurements on the new rhombohedral ternary compound Pr2Rh3Ge have been investigated. The synthesized polycrystalline compound was found to crystallize in the ternary ordered variant of the cubic Laves phase [Formula: see text]-type of structure with the space group R[Formula: see text]m, as previously reported. Pr2Rh3Ge exhibits a ferromagnetic behaviour below [Formula: see text] K, which was found to be unstable in low applied magnetic fields, revealing characteristics usually attributed to the long-range order. In the entire paramagnetic region electrical resistivity shows monotonous metallic conductivity character. We estimated that the Sommerfeld coefficient γ = 315 mJ/Pr-mol · [Formula: see text] of [Formula: see text] [Formula: see text]Ge is very large with comparison to ordinary metals which indicate the existence of heavy fermion behaviour of itinerant charge carriers at low temperatures or enhanced density of the quasi-particle state at the Fermi level. The crucial role of the crystalline electric field effects on the ground state properties of [Formula: see text] (J = 4) has been also observed. We think that the heavy fermion behaviour in [Formula: see text] [Formula: see text]Ge results from the dynamic low-lying crystal-field fluctuations, since there is no sign of Kondo effect in electrical resistivity and no enhancement of the slope S(T)/T in thermoelectric power data at low temperatures. It suggests that the conduction electrons at the Fermi level does not correlate with the 4f 2 states of [Formula: see text] atoms and hence there is no place for a typical spin Kondo effect, as it is commonly observed in Ce- and Yb-based heavy fermion systems.

Pr-magnetism in the quasi-skutterudite compound PrFe2Al8.

The intermetallic compound PrFe2Al8 that possesses a three-dimensional network structure of Al polyhedra centered at the transition metal element Fe and the rare earth Pr is investigated through neutron powder diffraction and inelastic neutron scattering in order to elucidate the magnetic ground state of Pr and Fe and the crystal field effects of Pr. Our neutron diffraction study confirms long-range magnetic order of Pr below [Formula: see text] K in this compound. Subsequent magnetic structure estimation reveals a magnetic propagation vector [Formula: see text] with a magnetic moment value of [Formula: see text]/Pr along the orthorhombic c-axis and evidence the lack of ordering in the Fe sublattice. The inelastic neutron scattering study reveals one crystalline electric field excitation near 19 meV at 5 K in PrFe2Al8. The energy-integrated intensity of the 19 meV excitation as a function of [Formula: see text] follows the square of the magnetic form factor of [Formula: see text] thereby confirming that the inelastic excitation belongs to the Pr sublattice. The second sum rule applied to the dynamic structure factor indicates only 1.6(2) [Formula: see text] evolving at the 19 meV peak compared to the 3.58 [Formula: see text] for free [Formula: see text], indicating that the crystal field ground state is magnetic and the missing moment is associated with the resolution limited quasi-elastic line. The magnetic order occurring in Pr in PrFe2Al8 is counter-intuitive to the symmetry-allowed crystal field level scheme, hence, is suggestive of exchange-mediated mechanisms of ordering stemming from the magnetic ground state of the crystal field levels.

Superconducting gap structure in the electron doped BiS2-based superconductor.

The influence of electron doping on semimetallic SrFBiS2 has been investigated by means of resistivity, zero and transverse - field (ZF/TF) muon spin relaxation/rotation (µSR) experiments. SrFBiS2 is semimetallic in its normal state and small amounts of La doping results in bulk superconductivity at 2.8 K, at ambient pressure. The temperature dependence of the superfluid density as determined by TF-µSR can be best modelled by an isotropic s - wave type superconducting gap. We have estimated the magnetic penetration depth [Formula: see text] nm, superconducting carrier density [Formula: see text] carriers m-3 and effective-mass enhancement m * = 1.558 m e. Additionally, there is no clear sign of the occurrence of spontaneous internal magnetic fields below [Formula: see text], which implies that the superconducting state in this material can not be categorized by the broken time-reversal symmetry which is in agreement with the previous theoretical prediction.

Cooperative magnetic behaviour in the new valence fluctuating compound Ce2Rh3Ge.

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.

Large Seebeck effect by charge-mobility engineering.

The Seebeck effect describes the generation of an electric potential in a conducting solid exposed to a temperature gradient. In most cases, it is dominated by an energy-dependent electronic density of states at the Fermi level, in line with the prevalent efforts towards superior thermoelectrics through the engineering of electronic structure. Here we demonstrate an alternative source for the Seebeck effect based on charge-carrier relaxation: a charge mobility that changes rapidly with temperature can result in a sizeable addition to the Seebeck coefficient. This new Seebeck source is demonstrated explicitly for Ni-doped CoSb3, where a marked mobility change occurs due to the crossover between two different charge-relaxation regimes. Our findings unveil the origin of pronounced features in the Seebeck coefficient of many other elusive materials characterized by a significant mobility mismatch. When utilized appropriately, this effect can also provide a novel route to the design of improved thermoelectric materials.

Electronic, magnetic, and transport properties of the isotypic aluminides SmT2Al10 (T = Fe, Ru).

We report the results of a comprehensive physical and magnetic property study of the new isotypic aluminides SmT2Al10 (T = Fe, Ru). These two compounds are members of a rare-earth based system which has become an exemplary case study of the interplay of magnetism and correlated electron phenomena. SmFe2Al10 and SmRu2Al10 are found to order in a putative antiferromagnetic spin arrangement at T(N) = 14.5 K and 12.5 K, respectively. Moreover, SmRu2Al10 shows a further phase transition at T(SR) = 5 K which is likely due to spin reorientation. The susceptibility of SmFe2Al10 points to a valence instability of the Sm ionic state at intermediate temperatures well above T(N). Electronic and thermal transport confirm that SmFe2Al10 undergoes an antiferromagnetic superzone gap formation below T(N), whereas SmRu2Al10 suffers a lattice anomaly driven magnetoelastic coupling at T(N). Below T(N), the physical properties of SmT2Al10 (T = Fe, Ru) are governed by magnons with an antiferromagnetic spin-wave spectrum that reveals spin-gap opening. Our findings in this work have exposed a new anomalous correlated compound in the RT2Al10 series. SmFe2Al10 has a magnetic ordered ground state in spite of an unstable valence at higher temperature. This is comparable with CeRu2Al10, which is a unique and controversial Kondo insulator that orders antiferromagnetic at T(N) = 27 K. Among the series of rare-earth RT2Al10 compounds, the presented Sm compounds are two new members with anomalously high magnetic ordering temperatures, and it is envisaged that together with the two very well studied compounds CeRu2Al10 and CeOs2Al10 our presented studies will enable a broader approach towards understanding the fascinating properties of this materials class.

Contiguous 3d and 4f magnetism: strongly correlated 3d electrons in YbFe2Al10.

We present magnetization, specific heat, and (27)Al NMR investigations on YbFe2Al10 over a wide range in temperature and magnetic field. The magnetic susceptibility at low temperatures is strongly enhanced at weak magnetic fields, accompanied by a ln(T0/T) divergence of the low-T specific heat coefficient in zero field, which indicates a ground state of correlated electrons. From our hard-x-ray photoemission spectroscopy study, the Yb valence at 50 K is evaluated to be 2.38. The system displays valence fluctuating behavior in the low to intermediate temperature range, whereas above 400 K, Yb(3+) carries a full and stable moment, and Fe carries a moment of about 3.1 µB. The enhanced value of the Sommerfeld-Wilson ratio and the dynamic scaling of the spin-lattice relaxation rate divided by T[(27)(1/T1T)] with static susceptibility suggests admixed ferromagnetic correlations. (27)(1/T1T) simultaneously tracks the valence fluctuations from the 4f Yb ions in the high temperature range and field dependent antiferromagnetic correlations among partially Kondo screened Fe 3d moments at low temperature; the latter evolve out of an Yb 4f admixed conduction band.

Investigations of the singlet ground state system: PrIrSi3.

We report our comprehensive study of physical properties of a ternary intermetallic compound PrIrSi3 investigated by dc magnetic susceptibility χ(T), isothermal magnetization M(H), thermo-remnant magnetization M(t), ac magnetic susceptibility χac(T), specific heat Cp(T), electrical resistivity ρ(T), muon spin relaxation (µSR) and inelastic neutron scattering (INS) measurements. A magnetic phase transition is marked by a sharp anomaly at Ttr = 12.2 K in χ(T) measured at low applied fields which is also reflected in the Cp(T) data through a weak anomaly at 12 K. An irreversibility between the zero field cooled and field cooled χ(T) data below 12.2 K and a very large relaxation time of M(t) indicates the presence of ferromagnetic correlation. The magnetic part of specific heat shows a broad Schottky-type anomaly near 40 K due to the crystal electric field (CEF) effect. An extremely small value of magnetic entropy below 12 K suggests a CEF-split singlet ground state which is confirmed from our analysis of INS data. The INS spectra show two prominent inelastic excitations at 8.5 meV and 18.5 meV that could be well accounted by a CEF model. The CEF splitting energy between the ground state singlet and the first excited doublet is found to be 92 K. Our µSR data reveal a possible magnetic ordering below 30 K, which is much higher than that found from the specific heat and magnetic susceptibility measurements. This could be due to the presence of short range correlations well above the long range magnetic ordering or due to the electronic changes induced by muons. The induced moment magnetism in the singlet ground state system PrIrSi3 with such a large splitting energy of 92 K is quite surprising.

Destruction of the Kondo effect in the cubic heavy-fermion compound Ce3Pd20Si6.

How ground states of quantum matter transform between one another reveals deep insights into the mechanisms stabilizing them. Correspondingly, quantum phase transitions are explored in numerous materials classes, with heavy-fermion compounds being among the most prominent ones. Recent studies in an anisotropic heavy-fermion compound have shown that different types of transitions are induced by variations of chemical or external pressure, raising the question of the extent to which heavy-fermion quantum criticality is universal. To make progress, it is essential to broaden both the materials basis and the microscopic parameter variety. Here, we identify a cubic heavy-fermion material as exhibiting a field-induced quantum phase transition, and show how the material can be used to explore one extreme of the dimensionality axis. The transition between two different ordered phases is accompanied by an abrupt change of Fermi surface, reminiscent of what happens across the field-induced antiferromagnetic to paramagnetic transition in the anisotropic YbRh2Si2. This finding leads to a materials-based global phase diagram--a precondition for a unified theoretical description.

Complex magnetic behavior in the novel Kondo lattice compound CeRhSn3.

We report the magnetic and transport properties of a new ternary intermetallic compound, CeRhSn3, using magnetic susceptibility, magnetization, specific heat, electrical resistivity, muon-spin relaxation (µSR) and neutron diffraction investigations. The dc magnetic susceptibility data reveal two magnetic phase transitions at 0.9 and 4 K. The overall behavior of dc susceptibility and magnetization indicates a ferrimagnetic-type phase transition near 4 K. The specific heat data also exhibit sharp λ-type anomalies at 1 and 4 K. The behavior of the specific heat anomaly under the application of a magnetic field suggests that the 1 K transition is probably related to a transition from a ferri- to a ferromagnetic state. The low temperature specific heat exhibits an enhanced Sommerfeld coefficient γ (~100 mJ mol⁻¹ K⁻²) due to the formation of a moderate heavy fermion state. The resistivity of CeRhSn3 demonstrates an interplay between the RKKY and Kondo interactions which is further modified by the presence of the crystal electric field. Interestingly, the resistivity of the nonmagnetic reference compound, LaRhSn3, is found to increase with decreasing temperature. Further, the onset of long-range magnetic order below 1 K is confirmed from our µSR study on CeRhSn3. However, the 4 K transition is not detected in the µSR and low temperature neutron diffraction data. Analysis of the dc magnetic susceptibility data within the framework of a two-sublattice model of ferrimagnetism supports the ferrimagnetic-type transition at 4 K in CeRhSn3. We have observed an unusual frequency dependence of the peak near 4 K in the ac susceptibility, which shows that the transition temperature shifts toward the lower temperature side with increasing frequency.

Dilution and non-Fermi-liquid effects in the CePtIn Kondo lattice.

Measurements of electrical resistivity (ρ(T)), magnetoresistivity (MR), magnetic susceptibility (χ(T)) and heat capacity (C(P)(T)) are presented for the (Ce(1-x)La(x))PtIn alloy system of which the CePtIn parent is a known dense Kondo compound that does not order magnetically down to 50 mK. χ(T) for alloys 0≤x≤0.8 exhibits Curie-Weiss behaviour. ρ(T) results indicate a transition from a dense Kondo behaviour for 0≤x≤0.2 to a single-ion Kondo region (0.3≤x≤0.8). The Kondo energy scale as given by T(K) values calculated from MR studies and by the temperature T(max)(ρ(mag)) where the magnetic contribution to ρ(T) exhibits a maximum value, is compared with theoretical models. It is shown that the experimental results not only depend on a volume effect as given by the compressible Kondo lattice model of Lavagna but in addition confirm the more complex behaviour recently presented by Burdin and Fulde for a Kondo alloy system in which the magnetic (Ce) and non-magnetic (La) atoms are distributed randomly. Non-Fermi-liquid behaviour is predicted by Burdin and Fulde at certain critical concentrations of the alloy system and experimental evidence for this is presented through χ(T), ρ(T) and C(P)(T) measurements.