Advancing Heteroanionicity in Zintl Phases: Crystal Structures, Thermoelectric and Magnetic Properties of Two Quaternary Semiconducting Arsenide Oxides, Eu8Zn2As6O and Eu14Zn5As12O.

Two novel quaternary oxyarsenides, Eu8Zn2As6O and Eu14Zn5As12O, were synthesized through metal flux reactions, and their crystal structures were established by single-crystal X-ray diffraction methods. Eu8Zn2As6O crystallizes in the orthorhombic space group Pbca, featuring polyanionic ribbons composed of corner-shared triangular [ZnAs3] units, running along the [100] direction. The structure of Eu14Zn5As12O crystallizes in the monoclinic space group P2/m and its anionic substructure can be described as an infinite "ribbonlike" chain comprised of [ZnAs3] trigonal-planar units, although the structural complexity here is greater and also amplified by disorder on multiple crystallographic positions. In both structures, the O2- anion occupies an octahedral void with six neighboring Eu2+ cations. Formal electron counting, electronic structure calculations, and transport properties reveal the charge-balanced semiconducting nature of these heteroanionic Zintl phases. High-temperature thermoelectric transport properties measurements on Eu14Zn5As12O reveal relatively high resistivity (ρ500K = 8 Ω·cm) and Seebeck coefficient values (S500K = 220 µV K-1), along with a low concentration and mobility of holes as the dominant charge-carriers (n500K = 8.0 × 1017 cm-3, µ500K = 6.4 cm2/V s). Magnetic studies indicate the presence of divalent Eu2+ species in Eu14Zn5As12O and complex magnetic ordering, with two transitions observed at T1 = 21.6 K and T2 = 9 K.

It Runs in the BaAl4 Family: Relating the Structure and Properties of Middle Child Ln2Co3Ge5 (Ln = Pr, Nd, and Sm) to its Siblings LnCo2Ge2 and LnCoGe3.

The BaAl4 prototype structure and its derivatives have been identified to host several topological quantum materials and noncentrosymmetric superconductors. Single crystals up to ∼3 mm × 3 mm × 5 mm of Ln2Co3Ge5 (Ln = Pr, Nd, and Sm) are obtained via flux growth utilizing Sn as metallic flux. The crystal structure is isostructural to the Lu2Co3Si5 structure type in the crystallographic space group C2/c. The temperature-dependent magnetization indicates magnetic ordering at 30 K for all three compounds. Pr2Co3Ge5 and Nd2Co3Ge5 exhibit complex magnetic behavior with spin reorientations before ordering antiferromagnetically around 6 K, whereas Sm2Co3Ge5 shows a clear antiferromagnetic behavior at 26 K. The structures and properties of Ln2Co3Ge5 (Ln = Pr, Nd, and Sm) are compared to those of the ThCr2Si2 and BaNiSn3 structure types. Herein, we present the optimized crystal growth, structure, and physical properties of Ln2Co3Ge5 (Ln = Pr, Nd, and Sm).

CoCrFeNi High-Entropy Alloy as an Enhanced Hydrogen Evolution Catalyst in an Acidic Solution.

High-entropy alloys (HEAs) have intriguing material properties, but their potential as catalysts has not been widely explored. Based on a concise theoretical model, we predict that the surface of a quaternary HEA of base metals, CoCrFeNi, should go from being nearly fully oxidized except for pure Ni sites when exposed to O2 to being partially oxidized in an acidic solution under cathodic bias, and that such a partially oxidized surface should be more active for the electrochemical hydrogen evolution reaction (HER) in acidic solutions than all the component metals. These predictions are confirmed by electrochemical and surface science experiments: the Ni in the HEA is found to be most resistant to oxidation, and when deployed in 0.5 M H2SO4, the HEA exhibits an overpotential of only 60 mV relative to Pt for the HER at a current density of 1 mA/cm2.

Annihilation and Control of Chiral Domain Walls with Magnetic Fields.

The control of domain walls is central to nearly all magnetic technologies, particularly for information storage and spintronics. Creative attempts to increase storage density need to overcome volatility due to thermal fluctuations of nanoscopic domains and heating limitations. Topological defects, such as solitons, skyrmions, and merons, may be much less susceptible to fluctuations, owing to topological constraints, while also being controllable with low current densities. Here, we present the first evidence for soliton/soliton and soliton/antisoliton domain walls in the hexagonal chiral magnet Mn1/3NbS2 that respond asymmetrically to magnetic fields and exhibit pair-annihilation. This is important because it suggests the possibility of controlling the occurrence of soliton pairs and the use of small fields or small currents to control nanoscopic magnetic domains. Specifically, our data suggest that either soliton/soliton or soliton/antisoliton pairs can be stabilized by tuning the balance between intrinsic exchange interactions and long-range magnetostatics in restricted geometries.

Magnetic order and fluctuations in the quasi-two-dimensional planar magnet Sr(Co1-xNix)2As2.

We use neutron scattering to investigate spin excitations in Sr(Co1-xNix)2As2, which has a c-axis incommensurate helical structure of the two-dimensional (2D) in-plane ferromagnetic (FM) ordered layers for 0.013⩽x⩽0.25. By comparing the wave vector and energy dependent spin excitations in helical ordered Sr(Co0.9Ni0.1)2As2 and paramagnetic SrCO2As2, we find that Ni doping, while increasing lattice disorder in Sr(Co1-xNix)2As2, enhances quasi-2D FM spin fluctuations. However, our band structure calculations within the combined density functional theory and dynamic mean field theory (DFT+DMFT) failed to generate a correct incommensurate wave vector for the observed helical order from nested Fermi surfaces. Since transport measurements reveal increased in-plane and c-axis electrical resistivity with increasing Ni doping and associated lattice disorder, we conclude that the helical magnetic order in Sr(Co1-xNix)2As2 may arise from a quantum order-by-disorder mechanism through the itinerant electron mediated Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions.

Controllable organic magnetoresistance in polyaniline coated poly(p-phenylene-2,6-benzobisoxazole) short fibers.

Herein, we first report a tunable organic magnetoresistance (OMAR) effect in polyaniline (PANI) coated acid treated poly(p-phenylene-2,6-benzobisoxazole) (t-PBO) short fibers. This unique OMAR is interpreted using the paramagnetic nature of PBO molecules combined with the localization length a0 calculated from the wave-function shrinkage model and forward interference model.

Ir d-band derived superconductivity in the lanthanum-iridium system LaIr3.

The electronic properties of the heavy metal superconductor [Formula: see text] are reported. The estimated superconducting parameters obtained from physical properties measurements indicate that [Formula: see text] is a BCS-type superconductor. Electronic band structure calculations show that Ir d-states dominate the Fermi level. A comparison of electronic band structures of [Formula: see text] and [Formula: see text] shows that the Ir-compound has a strong spin-orbit-coupling effect, which creates a complex Fermi surface.

Synthesis and characterization of a series of nickel(ii) alkoxide precursors and their utility for Ni(0) nanoparticle production.

A series of nickel(ii) aryloxide ([Ni(OAr)2(py)x]) precursors was synthesized from an amide-alcohol exchange using [Ni(NR2)2] in the presence of pyridine (py). The H-OAr selected were the mono- and di-ortho-substituted 2-alkyl phenols: alkyl = methyl (H-oMP), iso-propyl (H-oPP), tert-butyl (H-oBP) and 2,6-di-alkyl phenols (alkyl = di-iso-propyl (H-DIP), di-tert-butyl (H-DBP), di-phenyl (H-DPhP)). The crystalline products were solved as solvated monomers and structurally characterized as [Ni(OAr)2(py)x], where x = 4: OAr = oMP (1), oPP (2); x = 3: OAr = oBP (3), DIP (4); x = 2: OAr = DBP (5), DPhP (6). The excited states (singlet or triplet) and various geometries of 1-6 were identified by experimental UV-vis and verified by computational modeling. Magnetic susceptibility of the representative compound 4 was fit to a Curie Weiss model that yielded a magnetic moment of 4.38(3)µB consistent with a Ni2+ center. Compounds 1 and 6 were selected for decomposition studied under solution precipitation routes since they represent the two extremes of coordination. The particle size and crystalline structure were characterized using transmission electron microscopy (TEM) and powder X-ray diffraction (PXRD). The materials isolated from 1 and 6 were found by TEM to form irregular shape nanomaterials (8-15 nm), which by PXRD were found to be Ni0 hcp (PDF: 01-089-7129) and fcc (PDF: 01-070-0989), respectively.

Magnetoresistive polyaniline-silicon carbide metacomposites: plasma frequency determination and high magnetic field sensitivity.

The Drude model modified by Debye relaxation time was introduced to determine the plasma frequency (ωp) in the surface initiated polymerization (SIP) synthesized ß-silicon carbide (ß-SiC)/polyaniline (PANI) metacomposites. The calculated plasma frequency for these metacomposites with different loadings of ß-SiC nanoparticles was ranging from 6.11 × 10(4) to 1.53 × 10(5) rad s(-1). The relationship between the negative permittivity and plasma frequency indicates the existence of switching frequency, at which the permittivity was changed from negative to positive. More interestingly, the synthesized non-magnetic metacomposites, observed to follow the 3-dimensional (3-D) Mott variable range hopping (VRH) electrical conduction mechanism, demonstrated high positive magnetoresistance (MR) values of up to 57.48% and high MR sensitivity at low magnetic field regimes.

Manipulating the dimensional assembly pattern and crystalline structures of iron oxide nanostructures with a functional polyolefin.

Controlled crystalline structures (α- and γ-phase) and assembly patterns (1-D, 2-D and 3-D) were achieved in the synthesized iron oxide (Fe2O3) nanoparticles (NPs) using polymeric surfactant-polypropylene grafted maleic anhydride (PP-g-MA) with different concentrations. In addition, the change of the crystalline structure from the α- and γ-phase also led to the significantly increased saturation magnetization and coercivity.

Strengthened Magnetoresistive Epoxy Nanocomposite Papers Derived from Synergistic Nanomagnetite-Carbon Nanofiber Nanohybrids.

Novel papers based on epoxy nanocomposites with magnetite and carbon nanofiber (CNF) nanohybrids, without any surface modification to the nanofillers, show combined conductive, magnetic, and magnetoresistive properties. Negative magnetoresistance (MR) is observed in synthesized epoxy nanohybrid papers for the first time. These papers have potential applications for flexible electronics, magnetoresistive sensors, and the printing industry.

One-pot synthesis of size- and morphology-controlled 1-D iron oxide nanochains with manipulated magnetic properties.

Polypropylene grafted maleic anhydride (PP-MA, 2500 g mole(-1)) has demonstrated its unique capability to synthesize 1-D ferromagnetic hard (292.7 Oe) γ-Fe2O3 nanochains made of ~24 nm nanoparticles vs. PP-MA with 8000 g mole(-1) for the synthesis of 1-D ferromagnetic soft (70.5 Oe) γ-Fe2O3 nanochains (30 nm) made of flowerlike nanoparticles.

Magnetoresistive polyaniline/multi-walled carbon nanotube nanocomposites with negative permittivity.

Contrary to the observed positive giant magnetoresistance (GMR) in as-received multi-walled carbon nanotubes (MWNTs), pure polyaniline (PANI) synthesized with Cr(vi) as oxidant and MWNTs/PANI nanocomposites with ammonium persulfate (APS) as oxidant, a room temperature negative GMR of around -2% was reported in MWNTs/PANI nanocomposites with Cr(vi) as oxidant. Different from a frequency switch of permittivity from negative to positive in MWNTs/PANI nanocomposites with APS as oxidant, unique negative permittivity was observed in MWNTs/PANI nanocomposites with Cr(vi) as oxidant within the measured frequency range from 20 to 2 × 10(6) Hz. The obtained unique negative permittivity was explained by the plasma frequency from the Drude model, at which the permittivity changes from negative to positive and the material changes from a metamaterial to an ordinary dielectric medium. The observed positive and negative GMR behaviors in these disordered systems as verified by the temperature dependent resistivity exploration were well explained through a wave-function shrinkage model and orbital magnetoconductivity theory by calculating the changed localization length (a0).

Giant magnetoresistance in non-magnetic phosphoric acid doped polyaniline silicon nanocomposites with higher magnetic field sensing sensitivity.

Phosphoric acid doped conductive polyaniline (PANI) polymer nanocomposites (PNCs) reinforced with silicon nanopowders have been successfully synthesized using a facile surface initiated polymerization (SIP) method. The chemical structures of the nanocomposites are characterized using Fourier transform infrared (FT-IR) spectroscopy. The enhanced thermal stability of the silicon-PANI PNCs compared with pure PANI is obtained using thermogravimetric analysis (TGA). The obtained optical band gap of the PNCs using Ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS) decreases with increasing silicon loading. The dielectric properties of the PNCs are strongly related to the silicon loading level. Temperature dependent resistivity analysis reveals a quasi 3-D variable range hopping (VRH) electrical conduction mechanism for the synthesized PNCs. Room temperature giant magnetoresistance (GMR) is observed in the synthesized non-magnetic nanocomposites and analyzed using the wave-function shrinkage model.

Investigation of Fe incorporation in LnCr2Al20 (Ln = La, Gd, Yb) with 57Fe Mössbauer and single crystal X-ray diffraction.

Crystal growth, structure determination, and magnetic properties of LnCr2Al(20-x)Fe(x) (Ln = La, Gd, Yb) adopting the CeCr2Al20 structure type with space group Fd3m, a ∼ 14.5 Å, are reported. Single crystal X-ray diffraction and Mössbauer spectroscopy are employed to fully characterize the crystal structure of LnCr2Al(20-x)Fe(x) (Ln = La, Gd, Yb). LnCr2Al(20-x)Fe(x) (Ln = La, Gd, Yb) are the first pseudoternaries adopting the CeCr2Al20 structure type with a transition metal occupying the main group site. The Yb analogues are Pauli paramagnets with the Yb ion adopting an electronic configuration close to Yb(2+), while the Gd analogues show paramagnetic behavior with no magnetic order down to 3 K.

Microwave synthesized magnetic tubular carbon nanocomposite fabrics toward electrochemical energy storage.

Contrary to the helical carbon structure from pure cotton fabrics under microwave heating and radical oxidized ignition of nanoparticles from conventional heating, magnetic carbon tubular nanocomposite fabrics decorated with uniformly dispersed Co-Co(3)O(4) nanoparticles were successfully synthesized via a microwave heating process using cotton fabric and inorganic salt as precursors, which have shown better anti-corrosive performance and demonstrated great potential as novel electrochemical pseudocapacitor electrode.

Synthesis, structure, and properties of Ln2Ru3Al15 (Ln = Ce, Gd): comparison with LnRu2Al10 and CeRu4(Al,Si)(15.58).

Ln2Ru3Al15 (Ln = Ce, Gd) have been synthesized, and the competition between the growth of Ce2Ru3Al15 and CeRu2Al10 has been studied. The structure of Ce2Ru3Al15 was modified from the previously reported Ce2Ru3Al15 structure, and the structure of Gd2Ru3Al15 was determined for the first time. The magnetic and transport properties of Ln2Ru3Al15 were measured and compared to the properties of LnRu2Al10. Gd2Ru3Al15 orders antiferromagnetically at 21.0 K with a spin reorientation at 4.1 K and has a positive paramagnetic Curie-Weiss temperature of 11.5(17) K, suggesting strong ferromagnetic interactions within the structure. Ce2Ru3Al15 displays two low-temperature magnetic transitions at 3.7 and 3.1 K, the first of which is believed to be an antiferromagnetic ordering, with a θN of -7(3) K and a reduced moment of 2.33(4) µB/mol-Ce. Furthermore, the low-temperature magnetic and transport properties display the effects of Kondo screening of the magnetic moments. While structurally related, the properties of Ce2Ru3Al15 do not display the same anomalous features observed in CeRu2Al10.

Morphology and phase controlled cobalt nanostructures in magnetic polypropylene nanocomposites: the role of alkyl chain-length in maleic anhydride grafted polypropylene.

A novel function of maleic anhydride grafted polypropylene (PP) with different backbone chain-lengths was demonstrated, i.e., in controlling the cobalt morphologies (dispersed polyhedral vs. assembled chain nanostructure), crystalline structures (ε- vs. ß-phase), and magnetic property (242 vs. 808 Oe) in the synthesized magnetic PP nanocomposites.

Structural complexity meets transport and magnetic anisotropy in single crystalline Ln30Ru4Sn31 (Ln = Gd, Dy).

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.

Magnetic carbon nanostructures: microwave energy-assisted pyrolysis vs. conventional pyrolysis.

Magnetic carbon nanostructures from microwave assisted- and conventional-pyrolysis processes are compared. Unlike graphitized carbon shells from conventional heating, different carbon shell morphologies including nanotubes, nanoflakes and amorphous carbon were observed. Crystalline iron and cementite were observed in the magnetic core, different from a single cementite phase from the conventional process.