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The new plutunium based title compound is prepared from a mixture of the elements using Sn as a flux (Np:Pt:Si:Sn = 1:4:20:40, alumina crucible, slow temperature increase to 1050 °C, followed by slow cooling).

We report the observation of superconductivity in the CuIr${}_{2}$Se${}_{4}$ spinel induced by partial substitution of Pt for Ir. The optimal doping level for superconductivity in Cu(Ir${}_{1\ensuremath{-}x}$Pt${}_{x}$)${}_{2}$Se${}_{4}$ is $x$ $=$ 0.2, where ${T}_{c}$ is 1.76 K. A superconducting ${T}_{c}$ vs composition dome is established between the metallic, normal conductor CuIr${}_{2}$Se${}_{4}$ and semiconducting CuIrPtSe${}_{4}$. Electronic structure calculations show that the optimal ${T}_{c}$ occurs near the electron count of a large peak in the calculated electronic density of states and that CuIrPtSe${}_{4}$ is a band-filled insulator. Characterization of the superconducting state in this heavy metal spinel through determination of $\ensuremath{\Delta}C/\ensuremath{\gamma}{T}_{c}$ indicates that it is BCS-like. The relatively high upper critical field at the optimal superconducting composition [${H}_{c}$${}_{2}$(0) $=$ 3.2 T] is much larger than that reported for analogous rhodium spinels and is comparable to or exceeds the Pauli field (${\ensuremath{\mu}}_{0}{H}_{P}$), suggesting that strong spin-orbit coupling may influence the superconducting state. Further, comparison to doped CuIr${}_{2}$S${}_{4}$ suggests that superconductivity in iridium spinels is not necessarily associated with the destabilization of a charge-ordered spin-paired state through doping.

The structural behaviour under compression of different lanthanide (La, Gd, Ho, Yb) and actinide (Am) monochalcogenides is studied by means of in situ high-pressure x-ray diffraction. All the investigated compounds crystallize at ambient conditions within a cubic (B1) NaCl-type structure but show different behaviours at high pressures. LaTe and AmTe undergo B1 to B2 (CsCl-type structure) phase transitions, starting at 9 GPa and 12 GPa, respectively. The high-pressure phase of AmTe exhibits an electronic transition, identified by an anomaly in the compression curve which is accompanied by a sample colour change. The other three monochalcogenides studied here show clear evidence of decomposition and amorphization under pressure and are, to the best of our knowledge, the first in the LnTe series to show a pressure-induced amorphization. The bulk moduli of all B1-type structure compounds are calculated using the third-order Birch-Murnaghan equation of state.

The structural, magnetic, and thermodynamic properties of a new plutonium based compound, Pu 2 Pt 3 Si 5 , are reported. Single crystals produced by a Sn-flux technique have been analyzed showing a ferromagnetic behavior at 58 K. Pu 2 Pt 3 Si 5 crystallizes in the U 2 Co 3 Si 5 -type orthorhombic Iabm structure (s.g. 72) with atomic parameters a = 9.9226(2) A, b = 11.4436(2) A and c = 6.0148(1) A. The effective ( μ eff ∼0.74 μ B /Pu) and saturated ( σ sat ∼0.34 μ B /Pu) moments as well as the Sommerfeld coefficient ( γ e ∼2 mJ mol −1 K −2 /Pu) could point towards 5f localization in this material.

We used magnetic susceptibility, resistivity and heat capacity measurements to characterize the superconducting state in the Einstein solid VAl(10.1). We find that VAl(10.1) is a weak-coupling, type-II superconductor with T(c) = 1.53 K and an upper critical field of H(c2)(0) = 800 Oe. The heat capacity data in the range 0.07 K < T < 1.53 K are consistent with an isotropic energy gap of Δ(0) = 0.23 meV.

We have used a suite of diffraction, thermodynamic, and transport measurements to study the localized rattling of Al guest atoms in VAl${}_{10.1}$. The mean-square displacement of the rattling atom shows a concave-down temperature dependence. This is characteristic of an anharmonic vibration, the frequency of which increases with amplitude, akin to a particle in a box. We find that the rattling is best described in terms of a sixth-order interatomic potential, with negligible contributions from harmonic and quartic terms. The rattler has a characteristic temperature of ${\ensuremath{\theta}}_{RM}=21$ K and couples strongly to both the acoustic phonons and conduction electrons. The coupling to the phonons is evident from the large value of the Gr\"uneisen parameter, which increases with decreasing temperature to $\ensuremath{\Gamma}\ensuremath{\approx}43$ at 5 K. Below 6 K, the electrical resistivity varies as ${T}^{3}$, which can be explained in terms of electron scattering from damped sixth-order vibrations. VAl${}_{10.1}$ is a superconductor below ${T}_{c}=1.53$ K, with an upper critical field of $\ensuremath{\sim}$1 kG.

Several physical properties of the superconducting Heusler compounds, focusing on two systems (Y, Lu, Sc)Pd2Sn and APd2M, where A=Hf, Zr and M=Al, In, are summarized and compared. The analysis of the data shows the importance of the electron-phonon coupling for superconductivity in this family. We report the superconducting parameters of YPd2Sn, which has the highest Tc among all known Heusler superconductors., Comment: Accepted for publication in Phys. Rev. B

We report extensive measurements on a new compound (Yb0.24Sn0.76)Ru that crystallizes in the cubic CsCl structure. Valence-band photoemission (PES) and L3 x-ray absorption show no divalent component in the 4f configuration of Yb. Inelastic neutron scattering (INS) indicates that the eight-fold degenerate J-multiplet of Yb3+ is split by the crystalline electric field (CEF) into a ?7-doublet ground state and a ?8 quartet at an excitation energy 20 meV. The magnetic susceptibility can be fit very well by this CEF scheme under the assumption that a ?6-excited state resides at 32 meV; however, the ?8/?6 transition expected at 12 meV was not observed in the INS. The resistivity follows a Bloch-Gruneisen law shunted by a parallel resistor, as is typical of systems subject to phonon scattering with no apparent magnetic scattering. All of these properties can be understood as representing simple local moment behavior of the trivalent Yb ion. At 1 K there is a peak in specific heat that is too broad to represent a magnetic-phase transition, consistent with absence of magnetic reflections in neutron diffraction. On the other hand this peak also is too narrow to represent the Kondo effect in the ?7-doublet ground state. On the basis of the field dependence of the specific heat, we argue that antiferromagnetic (AF) short-range order (SRO) (possibly coexisting with Kondo physics) occurs at low temperatures. The long-range magnetic order is suppressed because the Yb site occupancy is below the percolation threshold for this disordered compound.

Superconductivity and structural characterization is reported for the Heusler structure compounds ${\text{ScRh}}_{2}\text{Sn}$, ${\text{LuRh}}_{2}\text{Sn}$, and ${\text{YRh}}_{2}\text{Sn}$. The superconducting ${T}_{\text{c}}$'s are 2.0 K, 2.9 K, and 4.1 K, respectively. The electronic contributions to the specific heat and the Debye temperatures are reported, and suggest that the observed trend in ${T}_{\text{c}}$ is governed primarily by an increase in electron-phonon coupling on going from ${\text{ScRh}}_{2}\text{Sn}$ to ${\text{YRh}}_{2}\text{Sn}$. The electron-phonon coupling constant ${\ensuremath{\lambda}}_{\text{ep}}$ and the normalized specific-heat jump $\ensuremath{\Delta}C/\ensuremath{\gamma}{T}_{\text{c}}$ suggest that the $M{\text{Rh}}_{2}\text{Sn}$ system evolves from weak coupling to moderate coupling superconductivity.

We have searched for time-reversal symmetry-breaking fields in the noncentrosymmetric superconductor ${\text{Mg}}_{10}{\text{Ir}}_{19}{\text{B}}_{16}$ via muon spin relaxation $(\ensuremath{\mu}\text{SR})$ in zero applied field. We also measured the temperature dependence of the superfluid density by muon spin rotation in transverse field to investigate the superconducting pairing symmetry in two polycrystalline samples of significantly different purities. In the high-purity sample, we detected no time-reversal symmetry-breaking fields greater than 0.05 G. The superfluid density was also found to be exponentially flat as $T\ensuremath{\rightarrow}0$ and so can be fit to a single-gap BCS model. In contrast, the lower purity sample showed an increase in the zero-field $\ensuremath{\mu}\text{SR}$ relaxation rate below ${T}_{c}$ corresponding to a characteristic field strength of 0.6 G. While the temperature dependence of the superfluid density was also found to be consistent with a single-gap BCS model, the magnitude as $T\ensuremath{\rightarrow}0$ was found to be much lower for a given applied field than in the case of the high-purity sample. These findings suggest that ${\text{Mg}}_{10}{\text{Ir}}_{19}{\text{B}}_{16}$ is a superconductor characterized by a single-gap function with no nodes and sample quality drastically affects the superconducting properties of this system.

The magnetic susceptibilities and specific heats of the crystalline garnet and glass forms of ${\text{Mn}}_{3}{\text{Al}}_{2}{\text{Si}}_{3}{\text{O}}_{12}$ are reported. This allows a direct comparison of the degree of magnetic frustration of the triangle-based garnet lattice and the structurally disordered solid at the same composition for isotropic spin $5/2\phantom{\rule{0.3em}{0ex}}{\text{Mn}}^{2+}\phantom{\rule{0.3em}{0ex}}(3{d}^{5})$. The results show that the glass phase shows more pronounced signs of magnetic frustration than the crystalline phase. Through comparison of the specific heats of ${\text{Ca}}_{3}{\text{Al}}_{2}{\text{Si}}_{3}{\text{O}}_{12}$ (grossular) and ${\text{Mn}}_{3}{\text{Al}}_{2}{\text{Si}}_{3}{\text{O}}_{12}$ (spessartine) garnets, information is provided concerning the anomalous extra specific heat in the latter material.

The ab initio structure determination of a novel unconventional noncentro-symmetric superconductor Mg{sub 10}Ir{sub 19}B{sub 16} (T{sub c} = 5 K) has been performed using a method that involves a combination of experimental data and calculations. Electron diffraction, X-ray powder diffraction, phase estimation routines, quantum mechanical calculations, high-resolution electron microscopy, and structural chemistry arguments are used. With the strengths of different methods used to eliminate the ambiguities encountered in others, the complete structure, including a very light B atom, has been determined with a high accuracy from impure polycrystalline powder samples, which suggests that the type of analysis described may be used to successfully address other similar intractable problems. The solved structure of Mg{sub 10}Ir{sub 19}B{sub 16} shows a complex nature that irregular coordination environments preclude a conversional description of compact packing of coordination polyhedra; however, it can be easier understood as ordered in an onion-skin-like series of nested polyhedra.

We report {sup 209}Bi nuclear-magnetic-resonance and nuclear-quadrupole-resonance measurements on a single crystal of the Kondo insulator U{sub 3}Bi{sub 4}Ni{sub 3}. The {sup 209}Bi nuclear-spin-lattice relaxation rate (T{sub 1}{sup -1}) shows activated behavior and is well fit by a spin gap of 220 K. The {sup 209}Bi Knight shift (K) exhibits a strong temperature dependence arising from 5f electrons, in which K is negative at high temperatures and increases as the temperature is lowered. Below 50 K, K shows a broad maximum and decreases slightly upon further cooling. Our data provide insight into the evolution of the hyperfine fields in a fully gapped Kondo insulator based on 5f electron hybridization.

Superconductivity in LaNiPO is disrupted by small (~5%) amounts of non-stoichiometry on the lanthanum site, even though the electronic contribution to the heat capacity increases with increasing non-stoichiometry. All samples also exhibit specific heat anomalies consistent with the presence of ferromagnetic spin fluctuations (Tsf ~ 14 K). Comparison of layered nickel phosphide and nickel borocarbide superconductors reveals different structure-property correlations in the two families., Comment: Submitted to Phys. Rev. B

We review the properties of Ni-based superconductors which contain Ni2X2 (X=As, P, Bi, Si, Ge, B) planes, a common structural element found also in the recently discovered FeAs superconductors. Strong evidence for the fully gapped nature of the superconducting state has come from field dependent thermal conductivity results on BaNi2As2. Coupled with the lack of magnetism, the majority of evidence suggests that the Ni-based compounds are conventional electron-phonon mediated superconductors. However, the increase in Tc in LaNiAsO with doping is anomalous, and mimics the behavior in LaFeAsO. Furthermore, comparisons of the properties of Ni- and Fe-based systems show many similarities, particularly with regards to structure-property relationships. This suggests a deeper connection between the physics of the FeAs superconductors and the related Ni-based systems which deserves further investigation., 21 pages, 4 figures, 3 tables; A review to appear in the Physica C special issue on superconducting pnictides

We report $^{75}$As Nuclear Magnetic Resonance data in a single crystal of CaFe$_2$As$_2$. The Knight shift, electric field gradient, and spin-lattice relaxation rate are strongly temperature dependent in the paramagnetic state, and change discontinuously at the structural transition temperature, $T_S=T_N=167$ K. Immediately below, the NMR spectra reveal an internal field at the As site associated with the presence of a commensurate magnetic order. These results indicate that the structural and magnetic transitions in CaFe$_2$As$_2$ are first order and strongly coupled, and that the electron density in the FeAs plane is highly sensitive to the out-of-plane structure.

We report the observation of superconductivity in ${\text{La}}_{3}{\text{Ni}}_{4}{\text{P}}_{4}{\text{O}}_{2}$ at 2.2 K. The layer stacking in this compound results in an asymmetric distribution of charge reservoir layers around the ${\text{Ni}}_{2}{\text{P}}_{2}$ planes. The estimated Wilson ratio, ${R}_{W}\ensuremath{\approx}5$, indicates the presence of strongly enhanced normal-state susceptibility, but many of the basic superconducting characteristics are conventional. The estimated electronic contribution to the specific heat, $\ensuremath{\gamma}\ensuremath{\approx}6.2\text{ }\text{mJ}\text{ }{\text{mol-Ni}}^{\ensuremath{-}1}\text{ }{\text{K}}^{\ensuremath{-}2}$, is about 2/3 of that found in layered nickel borocarbide superconductors.

We report an $^{75}$As NMR study of BaFe$_2$As$_2$ in both single crystals and polycrystal forms. We find that Sn impurities in the single crystal dramatically alter the low energy spin fluctuations and suppress the ordering temperature from 138 K to 85 K. In contrast to Sn-free samples, we find that the temperature dependence of the $^{75}$As NMR spectra and spin lattice relaxation rates reveal a second order phase transition to a state of incommensurate magnetic order.

We report the properties of two new isostructural compounds, U3Bi4Ni3 and U3Bi4Rh3. The first of these compounds is non-metallic, and the second is a nearly ferromagnetic metal, both as anticipated from their electron count relative to other U-based members of the larger 3-4-3 family. For U3Bi4Rh3, a logarithmic increase of C/T below 3 K, a resistivity proportional to T^4/3, and the recovery of Fermi-liquid behavior in both properties with applied fields greater than 3T, suggest that U3Bi4Rh3 may be a new example of a material displaying ferromagnetic quantum criticality.

Temperature-dependent dc susceptibility, heat capacity, and x-ray and neutron diffraction measurements on powder samples of the layered triangular-lattice material NaY02 reveal two successive phase transitions. At high temperature the structure is rhomobohedral, with all six inplane V-V distances equivalent. At T = 98K, the system undergoes a second order phase transition to a monoclinic intermediate temperature phase in which the in-plane Y -Y distances separate into four short and two long bonds, corresponding to orbital ordering of one electron per y3+. Below T 93K, there is a first order phase transition to a low temperature monoclinic phase, in which there are four long and two short in-plane Y -Y distances, consistent with orbital ordering of two electrons per y 3+ on a triangular lattice. Long range magnetic ordering of 0.98(2),uB per y 3 + (3d2) sets in at the T 93K structural transition. The low temperature structure ofNa Y02 displays orbital ordering that, although predicted by first principle calculations, has not previously been observed in this class of materials.

The magnetic properties and structure of ${\mathrm{Li}}_{x}\mathrm{Co}{\mathrm{O}}_{2}$ for $0.5lxl1.0$ are reported. ${\mathrm{Co}}^{4+}$ is found to be high spin in ${\mathrm{Li}}_{x}\mathrm{Co}{\mathrm{O}}_{2}$ for $0.94\ensuremath{\leqslant}x\ensuremath{\leqslant}1.00$ and low spin for $0.50\ensuremath{\leqslant}x\ensuremath{\leqslant}0.78$. Weak antiferromagnetic coupling is observed, and at $x\ensuremath{\approx}0.65$ the temperature-independent contribution to the magnetic susceptibility and the electronic contribution to the specific heat are largest. Neutron diffraction analysis reveals that the lithium oxide layer expands perpendicular to the basal plane and the Li ions displace from their ideal octahedral sites with decreasing $x$. Comparison of the structures of ${\mathrm{Na}}_{x}\mathrm{Co}{\mathrm{O}}_{2}$ and ${\mathrm{Li}}_{x}\mathrm{Co}{\mathrm{O}}_{2}$ reveals that the $\mathrm{Co}{\mathrm{O}}_{2}$ layer changes substantially with alkali content in the former but is relatively rigid in the latter, and that the $\mathrm{Co}{\mathrm{O}}_{6}$ octahedra in ${\mathrm{Li}}_{x}\mathrm{Co}{\mathrm{O}}_{2}$ are less distorted.

We report the synthesis and basic physical properties of single crystals of CaFe2As2, an isostructural compound to BaFe2As2 which has been recently doped to produce superconductivity. CaFe2As2 crystalizes in the ThCr2Si2 structure with lattice parameters a = 3.907(4) A and c = 11.69(2) A. Magnetic susceptibility, resistivity, and heat capacity all show a first order phase transition at T_0 171 K. The magnetic susceptibility is nearly isotropic from 2 K to 350 K. The heat capacity data gives a Sommerfeld coefficient of 8.2 +- 0.3 mJ/molK2, and does not reveal any evidence for the presence of high frequency (> 300 K) optical phonon modes. The Hall coefficient is negative below the transition indicating dominant n-type carriers., Published version, minor changes

Specific heat, electrical resistivity, and magnetic susceptibility measurements on a high quality sample of Mg10Ir19B16 provide a self-consistent determination of its superconducting properties. They indicate that Mg10Ir19B16 is a type-II superconductor [T{C}=4.45 K, kappa(0) approximately 20], with an electron-phonon coupling constant lambda{ep}=0.66. An analysis of the T-dependent specific heat shows that superconducting properties are dominated by an s-wave gap (Delta=0.7 meV). Point contact tunneling data provide evidence for multiple superconducting gaps, as expected from strong asymmetric spin-orbit coupling.

The intermetallic perovskite MgCNi3 is a superconductor with a Tc=7 K. Substitution of Fe and Ru for Ni decreases Tc monotonically as the doping concentration is increased. Here we report thermopower measurements, S(T), on MgCNi3, MgCNi3-xFex and MgCNi3-xRux. For MgCNi3, the thermopower is negative, - 12.5 mikroV/K, at 300 K. The absolute value of S decreases as x increases in MgCNi3-xFex and MgCNi3-xRux. The sign of S changes from negative to positive at low temperatures for values of x > 0.01. These data show that the carriers in MgCNi3 are electrons, and by increasing x and decreasing temperature, the participation of hole carriers clearly increases. The influence of the magnetic moments of the Fe atoms on the thermopower is not visible.

X-ray diffraction, specific heat, magnetic susceptibility and inelastic x-ray scattering measurements on the transurarium oxypnictides NpFeAsO and NpFeAsO0.85F0.15 are presented. No superconductivity down to 2 K was observed upon fluorine doping, contrary to the structurally analogous rare-earth pnictides. No modification of the phonon density of states was observed upon doping with fluorine. We discuss our results in light of the latest experimental and theoretical studies on the role of phonons in the superconducting pnictide compounds.

Mg10Ir19B16, a previously unreported compound in the Mg-Ir-B chemical system, is found to be superconducting at temperatures near 5 K. The fact that the compound exhibits a range of superconducting temperatures between 4 and 5 K suggests that a range of stoichiometries is allowed, though no structural evidence for this is observed. The compound has a large, noncentrosymmetric, body centered cubic unit cell with a=10.568 A, displaying a structure type for which no previous superconductors have been reported.

The synthesis, structure, and physical properties of five R-type Ru ferrites with chemical formula BaMRu5O11 (M=Li and Cu) and BaM′2Ru4O11 (M′=Mn, Fe and Co) are reported. All the ferrites crystallize in space group P63/mmc and consist of layers of edge sharing octahedra interconnected by pairs of face sharing octahedra and isolated trigonal bipyramids. For M=Li and Cu, the ferrites are paramagnetic metals with the M atoms found on the trigonal bipyramid sites exclusively. For M′=Mn, Fe and Co, the ferrites are soft ferromagnetic metals. For M′=Mn, the Mn atoms are mixed randomly with Ru atoms on different sites. The magnetic structure for BaMn2Ru4O11 is reported.

A co-gel of silica and Pd- and Co-containing cyanogel coordination polymer transforms into a silica composite material with embedded Pd/Co alloy nanoparticles upon heating at 600 °C. The nanoparticles are ferromagnetic and undergo a superparamagnetic transition between 50 and 75 K.

The superconductor MgCNi3 has been chemically doped by substitution of Ru and Fe for Ni and B for C. Neither ferromagnetism nor increasing TC is observed, suggesting that MgCNi3 has optimal superconducting properties at its intrinsic composition and electron count The effect of Carbon isotope substitution on Tc is reported: the carbon isotope effect coefficient is αc = 0.54±0.03. This indicates that carbon‐based phonons play a critical role in the superconductivity.

Charge density waves (CDWs) are periodic modulations of the conduction electron density in solids. They are collective states that arise from intrinsic instabilities often present in low dimensional electronic systems. The layered dichalcogenides are the most well-studied examples, with TiSe_2 one of the first CDW-bearing materials known. The competition between CDW and superconducting collective electronic states at low temperatures has long been held and explored, and yet no chemical system has been previously reported where finely controlled chemical tuning allows this competition to be studied in detail. Here we report how, upon controlled intercalation of TiSe_2 with Cu to yield Cu_xTiSe_2, the CDW transition is continuously suppressed, and a new superconducting state emerges near x = 0.04, with a maximum T_c of 4.15 K found at x = 0.08. Cu_xTiSe_2 thus provides the first opportunity to study the CDW to Superconductivity transition in detail through an easily-controllable chemical parameter, and will provide new insights into the behavior of correlated electron systems., Comment: Accepted to Nature Physics

Single phase samples of the monoclinic and orthorhombic polymorphs of Nb{sub 12}O{sub 29} have been identified and isolated. These polymorphs have different arrangements of nanometer dimension structural columns of ReO{sub 3}-type niobium oxygen arrays: They differ in structure after a 3-nm translation in one of three dimensions while being the same in the other two. Magnetic susceptibility measurements show that one polymorph displays an antiferromagnetic transition at 12 K, along with short-range order fluctuations up to 25 K, while the other shows strict Curie-Weiss behavior down to 2 K.

The crystal structure of boron-doped superconducting $\mathrm{Mg}{\mathrm{C}}_{1\ensuremath{-}x}^{11}\mathrm{B}_{x}{\mathrm{Ni}}_{3}$, studied by powder neutron diffraction, is reported. The solubility limit of boron is determined to be approximately $x=0.16$. The unit cell expands from $a=3.810\phantom{\rule{0.2em}{0ex}}89(2)\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}3.819\phantom{\rule{0.2em}{0ex}}66(2)\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ as $x$ increases from $x=0$ to $x=0.155$. Boron $(^{11}\mathrm{B})$ doping decreases ${T}_{c}$ with increasing $x$: from $7.09\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ $(x=0)$ to $6.44\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ $(x=0.155)$.

The effect of Carbon isotope substitution on T_c in the intermetallic perovskite superconductor MgCNi_3 is reported. Four independent groups of samples were synthesized and characterized. The average T_c for the Carbon-12 samples was found to be 7.12(2) K and the average T_c for the Carbon-13 samples was found to be 6.82(2) K. The resulting carbon isotope effect coefficient is alfa_C = 0.54(3). This indicates that carbon-based phonons play a critical role in the presence of superconductivity in this compound.

We present precise measurements of the upper critical field $({H}_{c2})$ in the recently discovered cobalt oxide superconductor. We have found that the critical field has an unusual temperature dependence; namely, there is an abrupt change of the slope of ${H}_{c2}(T)$ in a weak-field regime. In order to explain this result we have derived and solved Gor'kov equations on a triangular lattice. Our experimental results may be interpreted in terms of the field-induced transition from singlet to triplet superconductivity.

The superconductor $\mathrm{Mg}\mathrm{C}{\mathrm{Ni}}_{3}$ has been chemically doped by partial substitution of Ru for Ni in the solid solution $\mathrm{Mg}\mathrm{C}{\mathrm{Ni}}_{3\ensuremath{-}x}{\mathrm{Ru}}_{x}$ for $0lxl0.5$. Magnetic and specific heat measurements show that the Sommerfeld parameter $({\ensuremath{\gamma}}_{\mathrm{exp}})$ and ${T}_{C}$ decrease immediately on Ru substitution, but that a ${T}_{C}$ above $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is maintained even for a relatively large decrease in ${\ensuremath{\gamma}}_{\mathrm{exp}}$. Ferromagnetism is not observed to develop through Ru substitution, and the normal state magnetic susceptibility is suppressed.

The synthesis of three layer sodium cobalt oxide, NaxCoO2(x=0.3, 0.5, 0.6, 0.75 and 1.0) is reported. For x=0.6, 0.75, and 1.0, conventional solid-state synthesis was employed. x=0.3 and 0.5 were obtained via oxidative deintercalation of sodium at room temperature. x=0.3 can be hydrated to Na0.3CoO2•1.3H2O which is superconducting with a Tcof 4.3 K. Although having the same chemical stiochiometry as the previously reported two layer superconductor, it has a different stacking sequence of CoO2layers making it structurally distinct. Crystals of three layer NaCoO2show triangular morphology compared to hexagonal morphology for two layer Na0.7CoO2.

Although the microscopic origin of the superconductivity in high Tc copper oxides remains the subject of active inquiry, several of their electronic characteristics are well established as universal to all the known materials, forming the experimental foundation that all theories must address. The most fundamental of those characteristics is the dependence of the superconducting transition temperature on the degree of electronic band filling. Since the discovery of cuprate superconductivity in 1986 (1), the search for other families of superconductors that might help shed light on the superconducting mechanism of the cuprates has been of great interest. The recent report of superconductivity near 4K in the triangular lattice, layered sodium cobalt oxyhydrate, Na0.35CoO2.1.3H2O, is the best indication that superconductors related to the cuprates may be found (2). Here we show that the superconducting transition temperature of this compound displays the same kind of band-filling behavior that is observed in the cuprates. Specifically, that the optimal superconducting Tc occurs in a narrow range of band filling, and decreases for both underdoped and overdoped materials, in dramatic analogy to the phase diagram of the cuprate superconductors. Our results suggest that characterization of the detailed electronic and magnetic behavior of these new materials may help establish which of the many special characteristics of the cuprates is fundamental to their high Tc superconductivity., revised, publication information added

We report a corrected crystal structure for the CePt2In7 superconductor, refined from single crystal x-ray diffraction data. The corrected crystal structure shows a different Pt-In stacking along the c-direction in this layered material than was previously reported. In addition, all the atomic sites are fully occupied with no evidence of atom site mixing, resolving a discrepancy between the observed high resistivity ratio of the material and the atomic disorder present in the previous structural model The Ce-Pt distance and coordination is typical of that seen in all other reported Ce_nM_mIn_3n+2m compounds. Our band structure calculations based on the correct structure reveal three bands at the Fermi level that are more three dimensional than those previously proposed, and Density functional theory (DFT) calculations show that the new structure has a significantly lower energy., Comment: accepted by JPCM

Volumetric structures consisting of multilayer clads made of the bronze B10 and also of stellite SF6 alloys are prepared by laser remelting of the metal powder of the original particle size of ca 60 micrometers injected into the processing zone through a conical nozzle. For remelting with a cw CO 2 laser beam of intensities around 10 5 W/cm 2 and sample feed rates not exceeding 2.5 cm/s an efficient formation of the structures is observed and their geometry can be controlled. A fine grained, dendritic microstructure of the samples is observed by means of the optical and scanning microscopes. In the AFM scans the characteristic dimension of ca 60 nm reproduced in the periodic structures of the SF6 surface corresponds most probably to crystallines formed due to segregation after the liquid-solid phase transition. Similarly to SF6 the powderized B10 material is well suited for a fast prototyping.

An improvement of the reduction process through the presence of an extra copper pellet together with the Nd 2− x Ce x CuO 4 sample in an evacuated quartz tube is presented. Using this reduction technique, we have found that samples of Nd 1.85 Ce 0.15 Cu 1− y O 4− δ with copper deficiency y = 0.02 superconduct with T C = 23 K and the Meissner fraction is about 30%. X-ray diffraction (XRD) and energy dispersion X-ray analysis (EDAX) were used to characterize the surface of the samples. By means of DC magnetic measurement we have shown how deficiency and excess (2%) of copper in Nd 1.85 Ce 0.15 Cu 1± y O 4− δ influence the superconducting properties. At the end we compare the superconducting transition temperature of the samples treated in both the standard and modified reduction process.

The (Bi,Pb)–Sr–Ca–Cu–O glass–ceramics may be considered as disordered metal and superconductor. Depending on the heat treatment conditions the materials are either composed of the oval grains of the 2212 or 2201 phases embedded in the insulating matrix or they mainly contain the 2212 plate-like crystallites weakly connected one with another. The materials have large resistivity and usually large negative temperature coefficient of resistivity (TCR). The granular and disordered character of the materials is also reflected in their superconducting properties. Both the normal-state and superconducting properties correlate one with another. The glass–ceramic samples were obtained by annealing the amorphous solid at temperatures between 840 and 860 °C. The measurements of the temperature dependence of resistivity in annealed samples were carried out with the conventional four-terminal method in a temperature range from 3 to 300 K.

The upper critical field (Hc2) in the doped and undoped intermetallic superconductor MgCNi3 is studied. In MgCNi3−xMx (M = Ru, Fe), Hc2 decreases monotonically as x increases. In the case of Fe doping, Hc2 changes most dramatically: from 10.7 T at x = 0 to 7.9 T at x = 0.015, which might be caused by the fact that the 3d electrons in Fe break superconducting Cooper-pairs. Although, doping carbon on the boron site in Mg(B1−xCx)2 has a substantial effect on the upper critical field, here we report that for MgC1−xBxNi3, boron substitution slightly increases Hc2 for the lowest B doping level, x = 0.04, only. For x > 0.04 the upper critical field decreases slowly as x increases. The initial slope of Hc2(T) in MgC0.96B0.04Ni3 is nearly the same as that of pure MgCNi3.

We report the basic physical properties of monoclinic Y8Co5 determined by means of magnetic susceptibility, electrical resistivity, and specific heat measurements. The crystal structure of Y8Co5 is monoclinic (P2(1)/c) with lattice parameters a = 7.0582(6) Å, b = 7.2894(6) Å, c = 24.2234(19) Å, and β = 102.112(6)° as refined by using synchrotron powder x-ray diffraction data. The compound shows temperature independent paramagnetism with χ0 = 2.1 × 10(-3) emu mol(-1) and Sommerfeld parameter γ = 63 mJ mol(-1) K(-2). The calculated Wilson ratio for Y8Co5, R(W) = 1.4, is close to that expected for a free electron gas R(W) = 1. Low temperature resistivity under high pressure does not reveal superconductivity in this compound down to 1.2 K, up to hydrostatic pressures of 5.56 GPa. Band structure calculations (full-potential linearized augmented plane wave, FP-LAPW) derive the Stoner exchange interaction parameter S = 0.24, excluding magnetic behavior for Y8Co5.

The temperature dependencies of the in-plane ρ ab (T) and out-of-plane ρ c (T) resistivities of two groups of Nd 2 CuO 4 single crystals (films and bulk single crystals) was investigated in a temperature range 20-300 K. The effect of modified heated treatment and annealing conditions on transport properties of the pra-crystals Nd 2 CuO 4 was studied. It was found that nonstoichiometric disorder leads to different dependencies of the resistivity both ρ ab (T) and ρ c (T).

We report on the synthesis and physical characterization of a new compound, NpRh2Sn, prepared by arc-melting under argon atmosphere. Rietveld analysis of the powder x-ray diffraction pattern reveals an orthorhombic, Fe3C-type structure, with lattice parameters that are the shortest among the AnT2Sn series (An = U, Np, Pu, and T = Pd, Rh). A fit of the high-temperature magnetic susceptibility curve, χ(T), gives a Curie-Weiss temperature ΘCW = −29K, and an effective magnetic moment μeff = 2.42μB. The stabilization of the CW r eff r B antiferromagnetic order below TN = 34 K is revealed by a cusp in χ(T) and by a small anomaly in the specific heat curve, CP(T). An enhanced value of the Sommerfeld coefficient, γ ≈ 107 mJ mol−1 K−2, indicates a moderate heavy-fermion state. NpRh2Sn is the first member of the AnRh2Sn family, and a rare representative of heavy-fermion systems amidst Np- intermetallics.