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Emerging concepts of theranostics have led to the development of numerous multifunctional nanomaterials using various synthetic approaches. Herein, we report a simplistic approach towards the design of iron(III) phthalocyanine based pH responsive–magnetic–fluorescent nanoparticles for combined multimodal diagnosis and possible site selective therapy. Transmission electron micrographs (TEM) revealed distinct spherical (∼25–35 nm) nanoparticles, constituting a significantly stable nanodispersion which resulted from an appreciably high positive zeta potential (+21 mV) at pH 7.4. A transition in magnetic behavior of these nanoparticles (diamagnetism in bulk, paramagnetism in nanoparticles at room temperature and superparamagnetism at 200 K), in combination with acidic pH responsive loss of spherical shape, pH responsive release of chemotherapeutic agents in vitro, and confocal fluorescence microscopic images suggest potential utility of these materials as multimodal theranostic agents. A novel approach to the design of multifunctional theranostic devices, as demonstrated in this study, represents an important development in this area of scientific research.

The attractive/repulsive relationship between superconductivity and magnetic ordering has fascinated the condensed matter physics community for a century. In the early days, magnetic impurities doped into a superconductor were found to quickly suppress superconductivity. Later, a variety of systems, such as cuprates, heavy fermions, and Fe pnictides, showed superconductivity in a narrow region near the border to antiferromagnetism (AFM) as a function of pressure or doping. However, the coexistence of superconductivity and ferromagnetic (FM) or AFM ordering is found in a few compounds [RRh 4 B 4 (R = Nd, Sm, Tm, Er), R′Mo 6 X 8 (R′ = Tb, Dy, Er, Ho, and X = S, Se), UMGe (M = Ge, Rh, Co), CeCoIn 5 , EuFe 2 (As 1− x P x ) 2 , etc.], providing evidence for their compatibility. Here, we present a third situation, where superconductivity coexists with FM and near the border of AFM in Fe 1− x Pd x Te. The doping of Pd for Fe gradually suppresses the first-order AFM ordering at temperature T N/S , and turns into short-range AFM correlation with a characteristic peak in magnetic susceptibility at T ′ N . Superconductivity sets in when T ′ N reaches zero. However, there is a gigantic ferromagnetic dome imposed in the superconducting-AFM (short-range) cross-over regime. Such a system is ideal for studying the interplay between superconductivity and two types of magnetic (FM and AFM) interactions.

Arrays of nanowires and nanotubes of bismuth–tellurium (Bi–Te) were fabricated by electrodeposition techniques. Scanning electron microscopy was employed to characterize the morphology of the fabricated BiTe nanowires and nanotubes. The fabricated BiTe nanowire and nanotube arrays are shown to be polycrystalline with no preferred orientation. Wavelength dispersive spectroscopy analysis shows that either p-type (Bi rich) or n-type (Te rich) nanowires or nanotubes can be obtained by changing the electrodeposition potentials. The lamellar thickness of the nanowires and nanotube crystallites were determined using the Scherrer equation and found to be ∼17–24 nm. The Seebeck coefficient measurements at room temperature obtained for the nanowires and nanotubes deposited at −400 mV were +11.5 and +17 μV K−1, respectively, whereas those obtained at −65 mV were −48 and −63 μV K−1, respectively. The electrical resistance measurements indicated that the resistance of the nanowires and nanotubes decreased with increasing temperature, suggesting that these nanostructures behave like semiconductors.

Polyaniline (PANI) nanocomposites reinforced with tungsten oxide (WO3) nanoparticles (NPs) and nanorods (NRs) are fabricated via a facile surface-initiated-polymerization (SIP) method. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterizations reveal the uniform coating of polymer on the filler surface and a good dispersion of the nanofillers within the polymer matrix. Unique negative permittivity is observed in pure PANI and its nanocomposites. The switching frequency (frequency where real permittivity switches from negative to positive) can be easily tuned by changing the particle loading and filler morphology. Conductivity measurements are performed from 50∼290 K, and results show that the electron transportation in the nanocomposites follows a quasi 3-d variable range hopping (VRH) conduction mechanism. The extent of charge carrier delocalization calculated from VRH well explains the dielectric response of the metacomposites. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) reveal an enhanced thermal stability of the nanocomposites with the addition of nanofillers as compared to that of pure PANI.

Arrays of nanowires and nanotubes of antimony-telluride (Sb2Te3) have been fabricated by an electrodeposition technique. Scanning electron microscopy was employed to characterize the morphology and size of the fabricated Sb2Te3 nanowires and nanotubes. Wavelength dispersive spectroscopy analysis confirmed the composition of the fabricated nanowires and nanotubes. The composition of the nanowires fabricated at a cathodic current density of 10 mA cm−2 and nanotubes fabricated at a cathodic current density of 5.5 mA cm−2 was found to be ∼39% Sb and ∼61% Te (2 : 3 ratio between Sb and Te). The fabricated Sb2Te3 nanowire and nanotube arrays were found to be polycrystalline with no preferred orientation. The average lamellar thickness of the nanowires and nanotube crystallites was determined using the Scherrer equation and found to be ∼36 nm and ∼43 nm, respectively. The measured room temperature Seebeck coefficients for the Sb2Te3 nanowires and nanotubes were +359 µV K−1 and +332 µV K−1, respectively, confirming that the Sb2Te3 nanowires and nanotubes were p-type. The electrical resistance measurements indicated that the resistance of the Sb2Te3 nanowires and nanotubes decreased with increasing temperature, consistent with semiconducting behavior.

The magnetotransport properties of C–Fe films formed by e-beam vapor deposition onto glass substrates are presented in the temperature region of 2 K to 300 K. Hall effect measurements reveal a significant anomalous Hall voltage whose magnitude increases with increasing temperature. Measurements of the ordinary Hall coefficient in 10 nm-thick films reveal a charge carrier density ranging from n ≅ 3.0 × 1029 m−3 at 2 K to approximately half that value at 290 K. A comparison between anomalous Hall effect and parallel field magneto-optic Kerr effect measurements reveals a highly anisotropic coercive field with the easy direction lying in the plane of the film. Magnetoresistance measurements show that the films posses isotropic linear positive magnetoresistance beyond their saturation magnetization. The presence of carbon nanotubes formed during the e-beam process is confirmed via atomic force microscopy.

Polypyrrole (PPy) nanocomposites reinforced with tungsten oxide (WO3) nanoparticles (NPs) and nanorods (NRs) are fabricated by a surface-initiated polymerization method. The electrical conductivity is observed to depend strongly on the particle loadings, molar ratio of oxidant to pyrrole monomer, and the filler morphology. The electron transportation in the nanocomposites follows a quasi-three-dimensional variable range hopping (VRH) conduction mechanism as evidenced by the temperature-dependent conductivity function. Unique negative permittivity is observed in both pure PPy and its nanocomposites, and the switching frequency (frequency where the real permittivity switches from negative to positive) can be tuned by changing the particle loading, ratio of oxidant to pyrrole monomer, and the filler morphology. The extent of charge carrier localization calculated from the VRH mechanism is well-correlated to the dielectric properties of the nanocomposites. WO3 NRs are observed to be more efficient in improvin...

We report the flux growth and characterization of Ln2Ag1−xGa10−y (Ln=La, Ce), a disordered variant of the Ce2NiGa10 structure type. Single crystals of La2Ag1−xGa10−y (x∼0.3; y∼0.6) and Ce2Ag1−xGa10−y (x∼0.3; y∼0.9) were grown by the self-flux method and characterized using single-crystal X-ray diffraction. Transport measurements of Ce2Ag1−xGa10−y (x∼0.3; y∼0.9) reveal metallic behavior with a transition at 3 K. Magnetic measurements indicate antiferromagnetic ordering at 3 K of localized Ce3+ moments for Ce2Ag1−xGa10−y. Magnetoresistance is positive with a maximum value of 16% at 9 T. La2Ag1−xGa10−y exhibits metallic behavior with magnetic susceptibility showing temperature independent paramagnetism. We will compare Ce2Ag1−xGa10−y (x∼0.3; y∼0.9) to Ce2NiGa10 to examine the effects of transition metal substitution and to the related Ce(Ag,Ga)4 phase to examine the effects of crystal structure on the physical properties.

The morphology and thermal stability of bead-free and uniform electrospun pure polystyrene (PS) and PS/Ni nanocomposite fibers are investigated by SEM and TGA/DSC. A higher thermal stability is observed after introducing the nanoparticles in the polymer fibers. FT-IR analysis indicates a physical entanglement rather than chemical bonding between the nanoparticles and the polystyrene matrix. The nanoparticles still exhibit superparamagnetic properties even after dispersing in the polymer matrix, different from the reported enhanced coercivity as a result of the enlarged particle distance. However, the magnetic field required to saturate the magnetization is significantly reduced. A further oxidation is deduced after the high voltage electrospinning process.

Both pure polyimide (PI) and Fe-FeO nanoparticles reinforced PI nanocomposite fibers with a particle loading of 5, 10, 20, and 30 wt % are produced by electrospinning with optimized operational parameters such as polymer concentration, applied electrical voltage, and tip-to-collector distance. The morphology of the resulting products is correlated to the corresponding rheological behaviors of the pure PI and Fe-FeO/PI nanocomposite solutions. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) reveal an enhanced thermal stability of the nanocomposite fibers after introducing the Fe-FeO nanoparticles. The glass transition temperature (Tg) and melting temperature (Tm) of the nanocomposite fibers increase by 10−12 and 15−17 °C, respectively, as compared to those of the pure PI fibers. The magnetic properties of the Fe-FeO nanoparticles in the polymer nanocomposite fibers are different from those of the as-received nanoparticles. An increased shell thickness by 7.4% is deduced after t...

Single crystals of the Ln 2 MGa 12 (Ln=Pr, Nd, and Sm; M=Ni, Cu) family of compounds have been synthesized using Ga flux and characterized by single crystal X-ray diffraction. These phases are isostructural to Sm 2 NiGa 12 and crystallize in the tetragonal P 4/ nbm (no. 125, origin choice 2) space group, with Z =2 and lattice parameters a∼ 6.0 A and c∼ 15.3 A. These compounds order antiferromagnetically, and metallic behavior is observed in temperature ranges above the ordering temperature for each compound. Sm 2 CuGa 12 shows large positive magnetoresistance ∼130% in field up to 9 T.

Conductive polypyrrole/SiC nanocomposites are fabricated via a facile oxidative polymerization approach using p-toluene sulfonic acid as a dopant and ammonium persulfate as an oxidant. The effects of the nanoparticle loading, ratio of oxidant to monomers, and nanoparticle morphology (spheres and rods) on the physicochemical properties are investigated. Various characterization methods are carried out to determine the material properties. Thermal gravimetric analysis demonstrates an improved thermal stability of polypyrrole in the polymer nanocomposites (PNCs) with a higher decomposition temperature. The glass-transition temperature and melting temperature of the polymer and its nanocomposites are determined by differential scanning calorimetry with a decreased melting temperature of polypyrrole in the PNCs. The microstructures of pure polypyrrole and PNCs are observed by scanning electron microscopy. Powder X-ray diffraction analysis demonstrates the crytallinity of polypyrrole, and poor crystallinity is ...

Ln(4)FeGa(12), where Ln is Y, Tb, Dy, Ho, and Er, prepared by flux growth, crystallize with the cubic Y(4)PdGa(12) structure with the Im3m space group and with a = 8.5650(4), 8.5610(4), 8.5350(3), 8.5080(3), and 8.4760(3) A, respectively. The crystal structure consists of an iron-gallium octahedra and face-sharing rare-earth cuboctahedra of the Au(3)Cu type. Er(4)Fe(0.67)Ga(12) is iron-deficient, leading to a distortion of the octahedral and cuboctahedral environments due to the splitting of the Ga2 site into Ga2 and Ga3 sites. Further, interstitial octahedral sites that are unoccupied in Ln(4)FeGa(12) (Ln = Y, Tb, Dy, and Ho) are partially occupied by Fe2. Y(4)FeGa(12) exhibits weak itinerant ferromagnetism below 36 K. In contrast, Tb(4)FeGa(12), Dy(4)FeGa(12), Ho(4)FeGa(12), and Er(4)Fe(0.67)Ga(12) order antiferromagnetically with maxima in the molar magnetic susceptibilities at 26, 18.5, 9, and 6 K. All of the compounds exhibit metallic electric resistivity, and their iron-57 Mossbauer spectra, obtained between 4.2 and 295 K, exhibit a single-line absorption with a 4.2 K isomer shift of ca. 0.50 mm/s, a shift that is characteristic of iron in an iron-gallium intermetallic compound. A small but significant broadening in the spectral absorption line width is observed for Y(4)FeGa(12) below 40 K and results from the small hyperfine field arising from its spin-polarized itinerant electrons.

Iron oxide (α-phase) nanoparticles with coercivity larger than 300 Oe have been fabricated at a mild temperature by an environmentally benign method. The economic sodium chloride has been found to effectively serve as a solid spacer to disperse the iron precursor and to prevent the nanoparticles from agglomeration. Higher ratios of sodium chloride to iron nitrate result in smaller nanoparticles (19 nm for 20:1 and 14 nm for 50:1). The presence of polyvinyl alcohol (PVA) limits the particle growth (15 nm for 20:1 and 13 nm for 50:1) and favors nanoparticle dispersion in polymer matrices. Obvious physicochemical property changes have been observed with PVA attached to the nanoparticle surface. With PVA attached to the nanoparticle surface, the nanoparticles are found not only to increase the PVA cross-linking with an increase in melting temperature but also to enhance the thermal stability of the PVA. The nanoparticles are observed to be uniformly dispersed in the polymer matrix. Scanning electron microscopy (SEM) microstructure also shows an intermediate phase with a strong interaction between the nanoparticles and the polymer matrices, arising from the hydrogen bonding between the PVA and hydroxyl groups on the nanoparticle surface. The addition of nanoparticles favors the cross-linkage of the bulk PVA matrices, resulting in a higher melting temperature, and an enhanced thermal stability of the polymer matrix.

Iron nanoparticle reinforced polyacrylonitrile (PAN) nanocomposites are fabricated by a facile and environmentally benign solvent extraction method. Fourier transform infrared (FT-IR), thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC) results indicate a strong interaction between the iron nanoparticles and the polymer matrix for the as-prepared polymer nanocomposites. The heat treatment induces the carbonization of the polymer matrix. High-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) analysis show a protecting carbon shell surrounding the iron nanoparticles within the carbon matrix against the particle oxidation. The magnetic properties, electrical conductivity, and magnetic field dependent resistivity of heat-treated nanocomposites with different particle loadings are carried out in a physical properties measurement system by Quantum Design and by a standard four probe method. The saturation magnetization increases and the coercivity decrea...

The manufacturing of pure polyacrylonitrile (PAN) fibers and magnetic PAN/Fe3O4 nanocomposite fibers is explored by an electrospinning process. A uniform, bead-free fiber production process is developed by optimizing electrospinning conditions: polymer concentration, applied electric voltage, feedrate, and distance between needle tip to collector. The experiments demonstrate that slight changes in operating parameters may result in significant variations in the fiber morphology. The fiber formation mechanism for both pure PAN and the Fe3O4 nanoparticles suspended in PAN solutions is explained from the rheologial behavior of the solution. The nanocomposite fibers were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectrophotometer, and X-ray diffraction (XRD). FT-IR and XRD results indicate that the introduction of Fe3O4 nanoparticles into the polymer matrix has a significant effect on the crystallinity of PAN and a strong interaction between PAN and Fe3O4 nanoparticles. The magnetic properties of the nanoparticles in the polymer nanocomposite fibers are different from those of the dried asreceived nanoparticles.

Single crystals of Ln(Cu,Ga)13−x (Ln = La−Nd, Eu; x ≈ 0.2) were grown using Ga flux and their structures determined by single-crystal X-ray diffraction. The Ln(Cu,Ga)13−x (Ln = La−Nd, Eu; x ≈ 0.2), adopting NaZn13 structure type, crystallizes in the cubic Fm3c (No. 226) space group, with Z = 8 and lattice parameters a ≈ 11.8 A. Magnetic susceptibility and heat capacity measurements do not show any indication of long-range magnetic ordering down to 2 K for magnetic analogues. Metallic behavior is observed in the range of 2−300 K for each compound. A large positive magnetoresistance up to 154% at a field (μ0H) of 9 T is also observed for Pr(Cu,Ga)12.85(1). Most interestingly, the Pr analogue shows T2 temperature-dependent resistivity and satisfies Kadowaki-Woods relation, which is indicative of heavy-fermion behavior. Here, we present the crystal structures and physical properties of Ln(Cu,Ga)13−x (Ln = La−Nd, Eu; x ≈ 0.2).

Polyurethane (PU) nanocomposites reinforced with magnetic iron oxide nanoparticles and/or dielectric barium titanate nanoparticles fabricated by the surface-initiated-polymerization approach were investigated. The polymer matrix incorporated with different nanoparticles shows different presenting status surrounding the nanoparticles, i.e., chemical bonding, physical entanglement and bulk polymer chain. The nanoparticles have a different effect on the thermal stability of the polymer nanocomposites. By embedding different functional nanoparticles, unique physical properties were observed, such as enlarged coercivity and larger dielectric constant (real permittivity). The synergistic effect of the binary nanoparticle reinforced PU nanocomposite was explored. The addition of the iron oxide nanoparticles does have some effect on the permittivity. However, little difference was observed in the magnetic properties and permeability after the introduction of the dielectric barium titanate nanoparticle into Fe 2 O 3 /PU nanocomposites. The permeability and permittivity of γ-Fe 2 O 3 and BaTiO 3 nanoparticle reinforced PU nanocomposites were investigated with frequencies ranging from 10 MHz to 1 GHz. The predicted microwave properties from Bruggeman’s equation were consistent with the measured data, except for the real permittivity of Fe 2 O 3 /BaTiO 3 /PU. The volume average method (VAM) usually used for fiber-reinforced composites with reinforcements in the thickness direction was applied in this nanocomposite system. The predicted real permittivity by VAM was found to be in better agreement with the measured data than that predicted by Bruggeman’s equation.

The effect of iron oxide nanoparticle addition on the physicochemical properties of the polypyrrole (PPy) was investigated. In the presence of iron oxide nanoparticles, PPy was observed in the form of discrete nanoparticles, not the usual network structure. PPy showed crystalline structure in the nanocomposites and pure PPy formed without iron oxide nanoparticles. PPy exhibited amorphous structure and nanoparticles were completely etched away in the nanocomposites formed with mechanical stirring over a 7-h reaction. The thermal stability of the PPy in the nanocomposites was enhanced under the thermo-gravimetric analysis (TGA). The electrical conductivity of the nanocomposites increased greatly upon the initial addition (20 wt%) of iron oxide nanoparticles. However, a higher nanoparticle loading (50 wt%) decreased the conductivity as a result of the dominance of the insulating iron oxide nanoparticles. Standard four-probe measurements indicated a three-dimensional variable-range-hopping conductivity mechanism. The magnetic properties of the fabricated nanocomposites were dependent on the particle loading. Ultrasonic stirring was observed to have a favorable effect on the protection of iron oxide nanoparticles from dissolution in acid. A tight polymer structure surrounds the magnetic nanoparticles, as compared to a complete loss of the magnetic iron oxide nanoparticles during conventional mechanical stirring for the micron-sized iron oxide particles filled PPy composite fabrication.

Single crystals of Ln2MGa12 (Ln = La, Ce; M = Ni, Cu) have been synthesized using Ga flux and their structures determined by single-crystal X-ray diffraction. The Ln2MGa12 (Ln = La, Ce; M = Ni, Cu), which is isostructural to Ce2PdGa12, crystallizes in the tetragonal P4/nbm (No. 125, origin choice 2) space group, with Z = 2 and lattice parameters a ≈ 6.1 A and c ≈ 15.3 A. Ce2NiGa12 orders antiferromagnetically at 10 K and specific heat measurements suggest it is a moderate heavy-fermion system with γ ≈ 191 mJ mol−1 K−2. Magnetic susceptibility data show paramagnetic behavior down to 2 K for Ce2CuGa12, whereas specific heat data suggest a magnetic transition below 1.8 K, with a moderately enhanced γ-value of 69 mJ mol−1 K−2. Metallic behavior is observed below 300 K for each compound. A large positive and nonsaturating magnetoresistance up to 216% at a field (μ0H) of 9 T is also observed for La2NiGa12. We present the crystal structures and physical properties of the Ln2MGa12 (Ln = La, Ce; M = Ni, Cu) series.

Fe/Vinyl ester resin nanocomposites were fabricated by the monomer particle stabilization without any additional surfactant or coupling agent. Vinyl ester monomer serves as a coupling agent with one side covalently bound onto the nanoparticle surface by a displacement reaction and the other end copolymerized with extra vinyl ester resin to form a robust unity. The addition of iron nanoparticles favors the nanocomposite fabrication with a lower initial curing temperature. Vinyl ester resin in the nanocomposites becomes thermally stable as compared to the pure vinyl ester resin. An enhanced mechanical property is observed due to the uniform particle dispersion and the introduced interfacial covalent bondage. The iron nanoparticles become magnetically harder (with a larger coercivity) after dispersion in the vinyl ester resin matrix.

Ever since the discovery of high-Tc superconductivity in layered cuprates, the roles that individual layers play have been debated, due to difficulty in layer-by-layer characterization. While there is similar challenge in many Fe-based layered superconductors, the newly-discovered Ca10(Pt4As8)(Fe2As2)5 provides opportunities to explore superconductivity layer by layer, because it contains both superconducting building blocks (Fe2As2 layers) and intermediate Pt4As8 layers. Cleaving a single crystal under ultra-high vacuum results in multiple terminations: an ordered Pt4As8 layer, two reconstructed Ca layers on the top of a Pt4As8 layer, and disordered Ca layer on the top of Fe2As2 layer. The electronic properties of individual layers are studied using scanning tunneling microscopy/spectroscopy (STM/S), which reveals different spectra for each surface. Remarkably superconducting coherence peaks are seen only on the ordered Ca/Pt4As8 layer. Our results indicate that an ordered structure with proper charge balance is required in order to preserve superconductivity.

Ca10Pt3As8(Fe2As2)5 is a unique parent compound for superconductivity, which consists of both semiconducting Pt3As8 and metallic FeAs layers. We report the observation of superconductivity induced via chemical doping in either Ca site using rare-earth (RE) elements (RE = La, Gd) or Fe site using Pt. The interlayer distance and the normal-state physical properties of the doped system change correspondingly. The coupled changes include (1) superconducting transition temperature T c increases with increasing both doping concentration and interlayer distance, (2) our T c value is higher than previously reported maximum value for Pt doping in the Fe site, (3) both the normal-state in-plane resistivity and out-of-plane resistivity change from non-metallic to metallic behavior with increasing doping concentration and T c, and (4) the transverse in-plane magnetoresistance (MRab) changes from linear-field dependence to quadratic behavior upon increasing T c. For La-doped compound with the highest T c (~35 K), upper critical fields ([Formula: see text], [Formula: see text]), coherence lengths (ξ ab, ξ c), and in-plane penetration depth (λ ab) are estimated. We discuss the relationship between chemical doping, interlayer distance, and physical properties in this system.

The physical properties of metamagnetic Fe$_3$Ga$_4$ single crystals are investigated to explore the sensitivity of the magnetic states to temperature, magnetic field, and sample history. The data reveal a moderate anisotropy in the magnetization and the metamagnetic critical field along with features in the specific heat at the magnetic transitions $T_1=68$ K and $T_2=360$ K. Both $T_1$ and $T_2$ are found to be sensitive to the annealing conditions of the crystals suggesting that disorder affects the competition between the ferromagnetic (FM) and antiferromagnetic (AFM) states. Resistivity measurements reveal metallic transport with a sharp anomaly associated with the transition at $T_2$. The Hall effect is dominated by the anomalous contribution which rivals that of magnetic semiconductors in magnitude ($-5 \mu \Omega$ cm at 2 T and 350 K) and undergoes a change of sign upon cooling into the low temperature FM state. The temperature and field dependence of the Hall effect indicate that the magnetism is likely to be highly itinerant in character and that a significant change in the electronic structure accompanies the magnetic transitions. We observe a contribution from the topological Hall effect in the AFM phase suggesting a non-coplanar contribution to the magnetism. Electronic structure calculations predict an AFM ground state with a wavevector parallel to the crystallographic $c$-axis preferred over the experimentally measured FM state by $\approx$ 50 meV per unit cell. However, supercell calculations with a small density of Fe-antisite defects introduced tend to stabilize the FM over the AFM state indicating that antisite defects may be the cause of the sensitivity to sample synthesis conditions., Comment: 13 pages, 14 figures, and 4 supplementary tables

Pulsed ultrasonic experiments performed on the parent compounds of FeAs based superconductors $A$Fe${}_{2}$${\mathrm{As}}_{2}$ ($A=\text{Ba}$, Ca) revealed elastic anomalies that agree with a two-step process for the structural/magnetic transitions. Upon cooling, a pronounced velocity softening of longitudinal phonons propagating along the $\mathbit{c}$ axis is observed at the structural transition ${T}_{\mathrm{s}}$ due to a distortion of the lattice. Below a slightly lower temperature ${T}_{\mathrm{N}}$, a biquadratic coupling between the distortion and an antiferromagnetic order parameter produces a steep velocity stiffening upon further cooling, the stiffening being five times larger in ${\mathrm{CaFe}}_{2}$${\mathrm{As}}_{2}$ than in ${\mathrm{BaFe}}_{2}$${\mathrm{As}}_{2}$. Microwave resistivity measurements at 16.5 GHz suggest that, upon cooling, the lattice distortion at ${T}_{\mathrm{s}}$ is driven by magnetic fluctuations in ${\mathrm{BaFe}}_{2}$${\mathrm{As}}_{2}$, while it is rather due to lattice fluctuations in ${\mathrm{CaFe}}_{2}$${\mathrm{As}}_{2}$. This suggestion appears consistent with a second-order character of the transitions in ${\mathrm{BaFe}}_{2}$${\mathrm{As}}_{2}$ and a first-order one in ${\mathrm{CaFe}}_{2}$${\mathrm{As}}_{2}$.

Low energy electron diffraction, scanning tunneling microscopy and spectroscopy, and first-principles spin-dependent density functional theory are utilized to investigate the geometric, electronic, and magnetic structures of the stripe-ordered ($1\ifmmode\times\else\texttimes\fi{}2$) surface of $\mathrm{Ca}{({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x})}_{2}{\mathrm{As}}_{2}$ ($x=0$, 0.075). The surface is terminated with a 50% Ca layer. Compared to the bulk, the surface Ca layer has a large inward relaxation ($\ensuremath{\sim}0.5\text{ }\text{ }\AA{}$), and the underneath $\mathrm{As}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}\text{\ensuremath{-}}\mathrm{As}$ layer displays a significant buckling. First-principles calculations show that the ($1\ifmmode\times\else\texttimes\fi{}2$) phase is stabilized by the bulk antiferromagnetic spin ordering through the spin-charge-lattice coupling. Strikingly, a superconducting gap ($\ensuremath{\sim}7\text{ }\text{ }\text{meV}$ at 7.4 K) is observed to spatially coexist with the ($1\ifmmode\times\else\texttimes\fi{}2$) phase ($x=0.075$ compound). This implies the coexistence of both superconductivity and AFM ordering at the surface.

Transient liquid phase (TLP) bonding of Cu structures with a thin elemental Al intermediate bonding layer is being used to assemble Cu-based, enclosed, microchannel heat exchangers (MHEs). The heterogeneous Cu/Al/Cu TLP bonding interface region, formed during the TLP bonding process, impacts heat transfer of the assembled MHE device. To evaluate the thermal resistance of TLP bonded Cu/Al/Cu interface regions, transient flash measurements were performed across bonding interface regions formed under various conditions, in combination with detailed structural examination and measurements of bulk mass density and specific heat. The flash method is shown to yield quantitative measurements of interfacial thermal resistance values. Our results provide guidance to developing bonding protocols for Cu-based MHEs with optimized heat transfer performance.

Single crystals of the title compounds are grown from the elements (Ln:Ru:Sn = 12:6:11; evacuated silica tube, 1260 °C, 36 h).

We present the structure of Ln(30)Ru(4+x)Sn(31-y) (Ln = Gd, Dy) and the anisotropic resistivity, magnetization, thermopower, and thermal conductivity of single crystal Ln(30)Ru(4+x)Sn(31-y) (Ln = Gd, Tb). Gd(30)Ru(4.92)Sn(30.54) crystallizes in a new structure-type with space group Pnnm and dimensions of a = 11.784(1) Å, b = 24.717(1) Å, and c = 11.651(2) Å, and V = 3394(1) Å(3). Magnetic anisotropy and highly anisotropic electrical transport behavior were observed in the single crystals of Gd(30)Ru(4.92)Sn(30.54) and Tb(30)Ru(6)Sn(29.5). Additionally, the lattice thermal conductivity of Tb(30)Ru(6)Sn(29.5) is quite low, and a comparison is made to other Sn-containing compounds.

We report both experimental and theoretical investigations of the physical properties of Ba${}_{2}$Mn${}_{2}$Sb${}_{2}$O single crystals. This material exhibits a hexagonal structure with lattice constants $a=4.7029(15)$ \AA{} and $c=19.9401(27)$ \AA{}, as obtained from powder x-ray diffraction measurements, and in agreement with structural optimization through density functional theory (DFT) calculations. The magnetic susceptibility and specific heat show anomalies at ${T}_{\mathrm{N}}=60$ K, consistent with antiferromagnetic ordering. However, the magnitude of ${T}_{\mathrm{N}}$ is significantly smaller than the Curie-Weiss temperature ($|{\ensuremath{\Theta}}_{CW}|\ensuremath{\approx}560$ K), suggesting a magnetic system of reduced dimensionality. The temperature dependence of both the in-plane and out-of-plane resistivity changes from activated at $Tg{T}_{\mathrm{x}}\ensuremath{\sim}200$ K to logarithmic at $Tl{T}_{\mathrm{x}}$. Correspondingly, the magnetic susceptibility displays a bump at ${T}_{\mathrm{x}}$. DFT calculations at the DFT+$U$ level support the experimental observation of an antiferromagnetic ground state.

We report the electrical transport, magnetic, and thermodynamic properties of polycrystalline PdTe which exhibits superconductivity below 4.5 K. Using the measured values for the lower (H(c1)) and upper (H(c2)) critical fields, and the specific heat C(p), we estimate the thermodynamic critical field H(c)(0), coherence length ξ(0), penetration depth λ(0), and the Ginzburg-Landau parameter κ. Compared with band structure calculations, the density of states at the Fermi level is enhanced due to electron-phonon coupling with λ(ep) = 1.4. Furthermore, the large values of ΔC(p)/γ(n)T(c) and 2Δ(0)/k(B)T(c) suggest that PdTe is a strongly coupled superconductor.

We report the synthesis and structural and physical properties of CaFe${}_{4}$As${}_{3}$ single crystals. Needle-like single crystals of CaFe${}_{4}$As${}_{3}$ were grown out of Sn flux and the compound adopted an orthorhombic structure as determined by x-ray diffraction measurements. Electrical, magnetic, and thermal properties indicate that the system undergoes two successive phase transitions, occurring at ${T}_{N1}\ensuremath{\sim}90$ K and ${T}_{N2}\ensuremath{\sim}26$ K. At ${T}_{N1}$, electrical resistivities (${\ensuremath{\rho}}_{b}$ and ${\ensuremath{\rho}}_{ac}$) are enhanced while magnetic susceptibilities (${\ensuremath{\chi}}_{b}$ and ${\ensuremath{\chi}}_{ac}$) are reduced in both directions, parallel and perpendicular to the $b$ axis, consistent with the scenario of antiferromagnetic spin-density-wave formation. At ${T}_{N2}$, specific heat reveals a slope change, and ${\ensuremath{\chi}}_{ac}$ decreases sharply but ${\ensuremath{\chi}}_{b}$ shows a clear jump before it decreases again with decreasing temperature. Remarkably, both ${\ensuremath{\rho}}_{b}$ and ${\ensuremath{\rho}}_{ac}$ decrease sharply with thermal hysteresis, indicating the first-order nature of the phase transition at ${T}_{N2}$. At low temperatures, ${\ensuremath{\rho}}_{b}$ and ${\ensuremath{\rho}}_{ac}$ can be described by $\ensuremath{\rho}={\ensuremath{\rho}}_{0}+{AT}^{\ensuremath{\alpha}}$ (${\ensuremath{\rho}}_{0}$, $A$, and $\ensuremath{\alpha}$ are constants). Interestingly, these constants vary with applied magnetic field. The ground state of CaFe${}_{4}$As${}_{3}$ is discussed.

Atomically resolved structural and electronic properties of FeTe${}_{1\ensuremath{-}x}$Se${}_{x}$ ($x$ $=$ 0 and 0.45) have been studied with scanning tunneling microscopy/spectroscopy (STM/STS). In contrast to the extreme flatness of the Te-terminated FeTe surface, nanoscale chemical phase separation between Te and Se atoms is unambiguously revealed on the surface of FeTe${}_{0.55}$Se${}_{0.45}$. A statistical counting of the two kinds of atoms has the same ratio as that in the bulk. Remarkably, there is no electronic phase separation seen in the tunneling spectroscopy. This indicates that the optimally doped superconductor is chemically inhomogeneous but electronically homogeneous, in contrast to many correlated electron materials.

We report the synthesis and measurements of magnetic, transport, and thermal properties of polycrystalline ${\mathrm{Nb}}_{0.18}{\mathrm{Re}}_{0.82}$, which has a superconducting transition at ${T}_{c}$ \ensuremath{\sim} 8.8 K. The noncentrosymmetric \ensuremath{\alpha}-Mn structure of the compound is confirmed by x-ray diffraction. Using the measured values for the lower critical field ${H}_{c1}$, upper critical field ${H}_{c2}$, and the specific heat $C$, we estimate the thermodynamic critical field ${H}_{c}$(0), coherence length \ensuremath{\xi}(0), penetration depth \ensuremath{\lambda}(0), and the Ginzburg-Landau parameter \ensuremath{\kappa}(0). The specific heat jump at ${T}_{c}$, \ensuremath{\Delta}C/$\ensuremath{\gamma}{T}_{c}$ $=$ 1.86, suggests that ${\mathrm{Nb}}_{0.18}{\mathrm{Re}}_{0.82}$ is a moderately coupled superconductor. Below ${T}_{c}$ the electronic specific heat decays exponentially, suggesting that the gap is isotropic. Our data suggest that the triplet admixture is weak in the polycrystalline form of compound. However, the estimated value of the upper critical field ${H}_{c2}$(0) is close to the calculated Pauli limit.

Thermoelectric properties of the chemically-doped intermetallic narrow-band semiconductor FeGa3 are reported. The parent compound shows semiconductor-like behavior with a small band gap (Eg = 0.2 eV), a carrier density of ~ 10(18) cm-3 and, a large n-type Seebeck coefficient (S ~ -400 \mu V/K) at room temperature. Hall effect measurements indicate that chemical doping significantly increases the carrier density, resulting in a metallic state, while the Seebeck coefficient still remains fairly large (~ -150 \mu V/K). The largest power factor (S2/{\rho} = 62 \mu W/m K2) and corresponding figure of merit (ZT = 0.013) at 390 K were observed for Fe0.99Co0.01(Ga0.997Ge0.003)3., Comment: 5 pages, 4 figures, To be appear in Journal of Applied Physics

Single crystals of La2Ag0.7Ga9.4 and Ce2Ag0.7Ga9.1 are prepared from the elements by the self-flux method (alumina crucible, 1150 °C, 12 h; slow cooling).

We have synthesized polycrystalline samples of the noncentrosymmetric superconductor ${\text{Mo}}_{3}{\text{Al}}_{2}\text{C}$ by arc and RF melting, measured its transport, magnetic and thermodynamic properties, and computed its band structure. Experimental results indicate a bulk superconducting transition at ${T}_{c}\ensuremath{\sim}9.2\text{ }\text{K}$ while the density of states at the Fermi surface is found to be dominated by $\text{Mo}\text{ }d$ orbitals. Using the measured values for the lower critical field ${H}_{c1}$, upper critical field ${H}_{c2}$, and the specific heat $C$, we estimated the thermodynamic critical field ${H}_{c}(0)$, coherence length $\ensuremath{\xi}(0)$, penetration depth $\ensuremath{\lambda}(0)$, and the Ginzburg-Landau parameter $\ensuremath{\kappa}(0)$. The specific-heat jump at ${T}_{c}$, $\ensuremath{\Delta}C/\ensuremath{\gamma}{T}_{c}=2.14$, suggests that ${\text{Mo}}_{3}{\text{Al}}_{2}\text{C}$ is moderately to strongly coupled, consistent with the fast opening of the gap, as evidenced by the rapid release of entropy below ${T}_{c}$ from our electronic specific-heat measurements. Above 2 K the electronic specific heat exhibits the power-law behavior, suggesting that synthesis of single crystals and measurements at lower temperature are needed to establish whether the gap is anisotropic. The estimated value of the upper critical field ${H}_{c2}(0)$ is close to the calculated Pauli limit, therefore further studies are needed to determine whether the absence of an inversion center results in a significant admixture of the triplet component of the order parameter.

Ferromagnetic carbon-coated Fe nanoparticles (core size of 15 nm, saturated magnetization of Ms = 218 emu g−1 and coercivity of Hc = 62 Oe), fabricated at a mild temperature, demonstrate a strong ability to effectively remove more than 95 wt% of Cr(VI) in waste water via carbon shell physical adsorption, which is much higher than the commercially available Fe NPs.

Single crystals of LnFeSb(3) (Ln = Pr, Nd, Sm, Gd, and Tb) have been grown from excess Sb flux. The crystal structure consists of (infinity)(2)[FeSb(2)] octahedra separated by layers of Ln atoms and nearly square planar nets of (infinity)(2)[Sb(2)]. These compounds are metallic and display anisotropic magnetic properties. Long-range antiferromagnetic order is observed in the Sm, Gd, and Tb samples when the magnetic field is applied along the crystallographic a-axis. Evidence of magnetic ordering in all the samples is observed for the field applied parallel to the layers. The magnetic properties are well-described by considering only the magnetic interactions between the Ln 4f moments, with no contribution from the Fe sublattice. Herein, we report the crystal growth, structure, magnetization, transport, and chemical stabilities of the title compounds.

Ln(4)FeGa(12), where Ln is Y, Tb, Dy, Ho, and Er, prepared by flux growth, crystallize with the cubic Y(4)PdGa(12) structure with the Im3m space group and with a = 8.5650(4), 8.5610(4), 8.5350(3), 8.5080(3), and 8.4760(3) A, respectively. The crystal structure consists of an iron-gallium octahedra and face-sharing rare-earth cuboctahedra of the Au(3)Cu type. Er(4)Fe(0.67)Ga(12) is iron-deficient, leading to a distortion of the octahedral and cuboctahedral environments due to the splitting of the Ga2 site into Ga2 and Ga3 sites. Further, interstitial octahedral sites that are unoccupied in Ln(4)FeGa(12) (Ln = Y, Tb, Dy, and Ho) are partially occupied by Fe2. Y(4)FeGa(12) exhibits weak itinerant ferromagnetism below 36 K. In contrast, Tb(4)FeGa(12), Dy(4)FeGa(12), Ho(4)FeGa(12), and Er(4)Fe(0.67)Ga(12) order antiferromagnetically with maxima in the molar magnetic susceptibilities at 26, 18.5, 9, and 6 K. All of the compounds exhibit metallic electric resistivity, and their iron-57 Mossbauer spectra, obtained between 4.2 and 295 K, exhibit a single-line absorption with a 4.2 K isomer shift of ca. 0.50 mm/s, a shift that is characteristic of iron in an iron-gallium intermetallic compound. A small but significant broadening in the spectral absorption line width is observed for Y(4)FeGa(12) below 40 K and results from the small hyperfine field arising from its spin-polarized itinerant electrons.

Single crystals of Ln(Cu,Ga)13−x (Ln = La−Nd, Eu; x ≈ 0.2) were grown using Ga flux and their structures determined by single-crystal X-ray diffraction. The Ln(Cu,Ga)13−x (Ln = La−Nd, Eu; x ≈ 0.2), adopting NaZn13 structure type, crystallizes in the cubic Fm3c (No. 226) space group, with Z = 8 and lattice parameters a ≈ 11.8 A. Magnetic susceptibility and heat capacity measurements do not show any indication of long-range magnetic ordering down to 2 K for magnetic analogues. Metallic behavior is observed in the range of 2−300 K for each compound. A large positive magnetoresistance up to 154% at a field (μ0H) of 9 T is also observed for Pr(Cu,Ga)12.85(1). Most interestingly, the Pr analogue shows T2 temperature-dependent resistivity and satisfies Kadowaki-Woods relation, which is indicative of heavy-fermion behavior. Here, we present the crystal structures and physical properties of Ln(Cu,Ga)13−x (Ln = La−Nd, Eu; x ≈ 0.2).

We present the superconducting and critical current properties of ${\text{ZnNNi}}_{3}$ in the form of annularly coated carbon microfibers and thin films. The fibers were prepared by heating $6--8\text{ }\ensuremath{\mu}\text{m}$ diameter commercially available Ni-coated carbon fibers with Zn powder in a flowing stream of ${\text{NH}}_{3}$ gas at $650\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$. The fibers had a ${T}_{c}=3.75\text{ }\text{K}$, which was slightly higher than that of the polycrystalline powder and an upper critical field, ${H}_{c2}(0)=0.92\text{ }\text{T}$. Near the transition temperature ${T}_{c}$, the critical current density ${J}_{c}$ was well described by the Ginzburg-Landau power-law form ${[1\ensuremath{-}{(T/{T}_{c})}^{2}]}^{3/2}$. The extrapolation produces ${J}_{c}(0)\ensuremath{\cong}1.45\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{A}/{\text{cm}}^{2}$. An axial magnetic field produces an exponential decrease in the critical current density. Planar ${\text{ZnNNi}}_{3}$ films were formed on sapphire substrates by exposing thin Ni films to a similar heat treatment as the fibers. Hall measurements on the films in the normal state revealed a carrier density, $n=\ensuremath{-}1.46\ifmmode\times\else\texttimes\fi{}{10}^{23}\text{ }{\text{cm}}^{\ensuremath{-}3}$.

We compare and contrast the low-temperature magnetotransport properties of ultrathin, insulating Be films with and without spin-orbit scattering (SOS). Beryllium films have very little intrinsic SOS, but by ``dusting'' them with submonolayer coverages of Au, one can introduce a well-controlled SOS rate. Pure Be films with sheet resistance $Rg{R}_{Q}$ exhibit a low-temperature negative magnetoresistance (MR) that saturates to the quantum resistance ${R}_{Q}=h/{e}^{2}$. This high-field quantum metal phase is believed to represent a different ground state of the system. In contrast, the corresponding negative MR in Be/Au films is greatly diminished, suggesting that, in the presence of strong SOS, the quantum metal phase can only be reached at field scales well beyond those typically available in a low-temperature laboratory.

Single crystals of Ln2MGa12 (Ln = La, Ce; M = Ni, Cu) have been synthesized using Ga flux and their structures determined by single-crystal X-ray diffraction. The Ln2MGa12 (Ln = La, Ce; M = Ni, Cu), which is isostructural to Ce2PdGa12, crystallizes in the tetragonal P4/nbm (No. 125, origin choice 2) space group, with Z = 2 and lattice parameters a ≈ 6.1 A and c ≈ 15.3 A. Ce2NiGa12 orders antiferromagnetically at 10 K and specific heat measurements suggest it is a moderate heavy-fermion system with γ ≈ 191 mJ mol−1 K−2. Magnetic susceptibility data show paramagnetic behavior down to 2 K for Ce2CuGa12, whereas specific heat data suggest a magnetic transition below 1.8 K, with a moderately enhanced γ-value of 69 mJ mol−1 K−2. Metallic behavior is observed below 300 K for each compound. A large positive and nonsaturating magnetoresistance up to 216% at a field (μ0H) of 9 T is also observed for La2NiGa12. We present the crystal structures and physical properties of the Ln2MGa12 (Ln = La, Ce; M = Ni, Cu) series.

We present the transport and critical current measurements on carbon microfibers coated with 40-nm of polycrystalline $\ensuremath{\delta}\text{-MoN}$ and on carbon microfibers coated with 160 nm of ${\text{Mo}}_{3}{\text{Sb}}_{7}$. In each case the coatings where synthesized directly onto the $6\text{\ensuremath{-}}\ensuremath{\mu}\text{m}$ diameter carbon fibers. The superconducting transition temperature of the MoN microfibers was ${T}_{c}\ensuremath{\sim}13.1\text{ }\text{K}$, which is the highest temperature reported in any thin film form and is higher than what was reported for stoichiometric $\ensuremath{\delta}\text{-MoN}$, produced by high pressure synthesis. The transition temperature of the ${\text{Mo}}_{3}{\text{Sb}}_{7}$-coated microfibers ${T}_{c}=7.5\text{ }\text{K}$ was significantly higher than that observed in powder samples. Near the transition temperature ${T}_{c}$, the critical current density ${J}_{c}$ for both systems was well described by the power-law form ${[1\ensuremath{-}{(T/{T}_{c})}^{2}]}^{\ensuremath{\alpha}}$, where $\ensuremath{\alpha}=1.5$ is the Ginzburg--Landau exponent. We extrapolated ${J}_{c}(0)\ensuremath{\approx}5\ifmmode\times\else\texttimes\fi{}{10}^{7}\text{ }\text{A}/{\text{cm}}^{2}$ for the MoN microfibers and ${J}_{c}(0)\ensuremath{\approx}2.5\ifmmode\times\else\texttimes\fi{}{10}^{5}\text{ }\text{A}/{\text{cm}}^{2}$ for the ${\text{Mo}}_{3}{\text{Sb}}_{7}$ fibers.

We report on the magnetization and electrical resistivity on single crystals of $\mathrm{Ce}\mathrm{Cr}{\mathrm{Sb}}_{3}$, a ferromagnetic metal with large anisotropy. It undergoes two ferromagnetic transitions: the first is at ${T}_{\mathrm{Cr}}=115\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ due to the electrons from the Cr ions and the second is a gradual alignment of the ${\mathrm{Ce}}^{3+}\phantom{\rule{0.2em}{0ex}}4f$ electrons between 48 and $18\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The Cr moments behave similarly in $\mathrm{La}\mathrm{Cr}{\mathrm{Sb}}_{3}$, with the easy axis along the $b$ axis. Below $48\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the Ce moments begin to align along the $c$ axis, and as the applied field increases, their effect on the magnetization increases in importance, resulting in nearly linear behavior of ${M}_{c}(T)$ for $H=30\phantom{\rule{0.3em}{0ex}}\mathrm{kG}$. At $5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the saturation moment along the $c$ axis is $3.28{\ensuremath{\mu}}_{B}∕\mathrm{f.u.}$, and along the $b$ axis, the magnetization saturates to $1.29{\ensuremath{\mu}}_{B}∕\mathrm{f.u.}$, the difference being only 7% less than the predicted Hund's rule value for ${\mathrm{Ce}}^{3+}$, indicating that the $4f$ moments have fully aligned along the $c$ axis.