Crystal structure and physical properties of a magnetic molecular conductor (EDO-TTFVODS)2FeCl4

Crystal structure, and electrical conducting and magnetic properties of a radical cation salt of EDO-TTFVODS with magnetic FeCl₄^? ion, (EDO-TTFVODS)₂FeCl₄ (EDO-TTFVODS = ethylenedioxytetrathiafulvalenoquinone-1,3-diselenolemethide) are reported. In this salt, there are two independent donor molecules formed two different layers A and B, and the counter FeCl₄^? ions layer is sandwiched between two donor layers A and B along the b-axis. The donor molecules form the one-dimensional columns along the a-axis in both donor layers. This salt shows high conductivity at room temperature (σ_RT = 25 S cm^?1) and a metallic behavior down to ca. 80 K, where a metal–insulator transition however occurs. The magnetic susceptibility obeys a Curie–Weiss law (Curie constant C = 4.42 emu K mol^?1 and Weiss temperature Θ = ?1.5 K), without any magnetic ordering down to 1.8 K. This result suggests the weak antiferromagnetic interaction between the d spins of FeCl₄^? ions.     

The influence of Er substitution on magnetic and magnetocaloric properties of Dy1−xErxCo2 solid solutions

Magnetic and heat capacity measurements have been carried out on polycrystalline Dy_1?xEr_xCo₂ solid solutions (0 ≤ x ≤ 0.3). Powder X-ray diffraction at room temperature revealed that all Dy_1?xEr_xCo₂ solid solutions consist of the C15 cubic Laves phase MgCu₂ type structure. These solid solutions are ferromagnetic with a Curie temperature T_C below 138 K. Their Curie temperatures decrease from 138 K for DyCo₂ to 106 K for Dy_0.7Er_0.3Co₂. At higher temperatures, all solid solutions are Curie–Weiss paramagnets. Both magnetic and heat capacity measurements showed that all samples undergo a first-order type phase transition at T_C from paramagnetic to ferromagnetic state. Heat capacity measurements allowed us to determine the Debye temperature. The magnetocaloric effect has been estimated both in terms of isothermal magnetic entropy change and adiabatic temperature change in magnetic fields up to maximum 3 T.     

Porous polyaniline films with high conductivity

Porous polyaniline (PANI) films with high conductivity at room temperature have been prepared by a new method called ‘doping-dedoping-redoping’. The room-temperature conductivity of the resulting PANI films doped with HCl, HClO₄, H₂SO₄, H₃PO₄ and p-toluene sulfonic acid (p-TSA), can reach 200–300 S cm⁻¹, which is comparable with the results of PANI films doped with camphor sulfonic acid (CSA) in m-cresol. It has been demonstrated that the resulting PANI chains still keep the expanded conformation like PANI-CSA in m-cresol, which may be why high room-temperature conductivity can be obtained by this new method. Moreover, the electrical and mechanical properties of the resulting PANI films have been measured as a function of the protonation state, temperature and dopants.     

铁离子掺杂聚苯胺涂层的光热杀菌性能

选用聚苯胺（PANI）作为光热材料,采用三氯化铁作为掺杂剂制备铁离子掺杂PANI纳米线,通过静电吸附将铁离子掺杂PANI纳米线均匀负载于纤维素膜表面,形成了PANI杀菌涂层,采用红外（FT-IR）、X射线衍射（XRD）和扫描电子显微镜（SEM）研究材料的结构;通过紫外可见吸收光（UV-vis）和光热升温测试研究材料的吸光和光热性能;通过热重分析仪（TG）研究材料的热稳定性,以闪光灯作光源,选大肠杆菌作为试验菌株,研究涂层的光热杀菌性能。结果表明,铁离子与PANI发生络合,铁离子掺杂PANI的吸光强度、光热转换性能、热稳定性比酸掺杂PANI明显增加,酸掺杂PANI涂层杀菌率为76%,铁离子掺杂PANI涂层杀菌率可达100%。     

Specific features of magnetic order in a multiferroic compound CuCrO<Subscript>2</Subscript> determined using NMR and NQR data for <Superscript>63, 65</Superscript>Cu nuclei

Results of studying the paramagnetic and ordered phases of a CuCrO₂ single crystal using nuclear magnetic and nuclear quadrupole resonances on ^63,65Cu nuclei are presented. The measurements have been carried out in wide ranges of temperature (T = 4.2–300 K) and magnetic-field strength (Н = 0–94 kOe), with the magnetic fields being directed along a and c axes of the crystal. The components of the electric-field gradient tensor and the magnetic-shift tensor (K _a,c) have been determined. The temperature dependences K _a(H || a) and K _c(H || c) for the paramagnetic phase are described by the Curie–Weiss law and reproduce the behavior of the magnetic susceptibility (χ_a,c). The hyperfine field on a copper nucleus has been determined, which is equal to h _hf ^a,c = 33 kOe/μB. Below the temperature Т _N = 23.6 K, nuclear magnetic resonance and nuclear quadrupole resonance spectra for ^63,65Cu nuclei have been recorded typical of helical magnetic structures, which are incommensurable with the lattice period.     

Structural and physical properties of the U9Fe7Ge24 uranium germanide

A new ternary compound, U₉Fe₇Ge₂₄, was synthesized by arc-melting the elements, followed by annealing at 900 °C. This compound was characterized by single crystal and powder X-ray diffraction, magnetization, specific heat and electrical transport measurements. It crystallizes in an original tetragonal structure type (space group I4/mmm), with lattice parameters a = 12.3789(2) Å and c = 18.2881(3) Å. Three uranium, eighth germanium, and three iron crystallographic sites exist in this structure, with the atoms making a stacking of infinite chains along the a and b axis. From their interatomic distances strong interactions between the uranium and germanium atoms can be predicted. The magnetic and specific heat measurements down to 2 K do not show any magnetic transition. The Curie–Weiss behaviour with a negative paramagnetic Curie temperature θp = ?94 K and reduced effective magnetic moment of μ_eff = 2.13 μ_B/U indicate that the compound is rather far from onset of magnetism, presumably due to a strong hybridisation of the 5f and ligand states. The electrical transport measurements show a metallic behaviour.     

Structural,magnetic and 151Eu Mössbauer studies of mechanosynthesized nanocrystalline EuCr1−xFexO3 particles

We report on the mechanosynthesis of single-phased EuCr_1?xFe_xO₃ (x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) nanocrystalline particles (～20–50 nm) at temperatures that are significantly lower than those at which the corresponding bulk materials are conventionally synthesized, and their structural and magnetic characterization. It was found that the average crystallite size decreased, the lattice parameters increased and the unit cell gets more distorted with increasing x. All samples showed weak ferromagnetism due to spin canting. Although Curie temperatures increase with increasing x, they are significantly lower than those of the corresponding bulk materials. Simple Curie–Weiss fits for the paramagnetic susceptibilities were found to be more physically plausible relative to fits where Vleck-type contributions to the paramagnetic susceptibilities due to Eu³⁺ ionic sublattices, which are separate from of the Cr³⁺/Fe³⁺ ones, were assumed. The non-existence of such separate Eu³⁺ and Cr³⁺/Fe³⁺ sublattices was further supported by ¹⁵¹Eu Mössbauer spectra of the nanoparticles which favor a non-equilibrium cation distribution wherein a considerable amount of Eu³⁺ and Cr³⁺/Fe³⁺ ions exchange their normal dodecahedral and octahedral perovskite-related sites, respectively. The supertransferred hyperfine magnetic field at the site of the ¹⁵¹Eu nuclei, induced by neighboring Cr³⁺/Fe³⁺ ions, was found to be considerably larger for B-site nuclei than for A-site ones. The antisite behavior concluded in this study is consistent with ⁵⁷Fe Mössbauer spectral analysis of the nanoparticles that favor the presence of the majority of the Fe³⁺ ions at the usual B-sites and minority Fe³⁺ ions either at the A-sites or at B-sites with Eu³⁺/Cr³⁺ nearest B-site neighbors. The relative site occupancies associated with the cationic site exchange inferred from both the ¹⁵¹Eu and ⁵⁷Fe Mössbauer spectra are remarkably consistent.     

Magnetic,electronic and thermodynamic properties of the heavy fermion compound CeNiAl4

We have carried out the magnetic susceptibility, electrical resistivity, specific heat, thermoelectric power and X-ray photoemission spectroscopy (XPS) measurements for CeNiAl₄. The magnetic susceptibilities have revealed a Curie–Weiss behavior above 30 K with a large negative paramagnetic Curie temperature θ_P = ?66 K and an effective moment of 2.45μ_B. The f-occupancy and the coupling between the f level and the conduction states are derived from XPS to be about 0.83 and ～40–64 meV, respectively. The valence state of the Ce ion is close to 3+. Extrapolation of the lowest temperatures range of C/T(T²) yields the electronic specific heat coefficient γ = 0.5 J mol^?1 K^?2. In combination with the thermoelectric power and resistivity data, a heavy fermion state is confirmed in CeNiAl₄.     

EPR studies of blends of polyaniline with poly(methyl methacrylate-co-glycidyl methacrylate iminodiacetic acid)

A novel conductive blends of polyaniline (PANI) with poly(methyl methacrylate-co-glycidyl methacrylate iminodiacetic acid) (PANI–PMGI) was prepared by in situ dispersion polymerization. The PANI–PMGI blends were characterized by UV–vis, FTIR and electron paramagnetic resonance (EPR) spectra. The structure of the PANI–PMGI blends was similar to emeraldine salt proved by UV–vis and FTIR. The value of ΔH_pp, lineshape, g factor, N_s and A/B ratio of blends were investigated by EPR. The results of EPR indicated that the intermolecular interaction between PANI and PMGI was dependent on the content of PANI and temperature.     

The ternary Er–Co–Sn system

The isothermal section of the phase diagram of the Er–Co–Sn ternary system has been constructed at 670 K. The existence of seven ternary intermetallic compounds which crystallize with known structure types has been confirmed. The temperature dependence of the magnetic susceptibility (χ) for ErCo₃Sn and Er₃Co₆Sn₅ has been measured. The ErCo₃Sn stannide orders ferrimagnetically at 24 K, and the Er₃Co₆Sn₅ stannide is a Curie–Weiss paramagnet. For Er₃Co₆Sn₅, electrical resistivity (ρ) and differential thermopower (α) have been measured in the range 80–400 K.     

Magnetoresistance of the metallic polyacetylene

The temperature dependence of the zero field resistivity, ρ(T), and the magnetoresistance (MR) of polyacetylene (PA) doped with iodine, metal-halide (AuCl₃, FeCl₃) and perchlorate are measured. The results of doped PA are different for each dopant and for the degree of aging. The ρ(T) of the metal-halide and the perchlorate doped PAs show a resistivity minimum near T*≈200 K and the weak temperature dependence at low temperature. In particular, some of the perchlorate doped PA samples show the positive temperature coefficient of resistivity (TCR) from T=1.5 K to T=300 K with resistivity ratio ρ(T=1.5 K)/ρ(T=300 K)=0.5∼0.7 depending on the samples. The MR is negative for all of the metallic PA samples. Both transverse (J⊥H) and longitudinal (J6H) MR show similar magnetic field dependencies, although the magnitude of the transverse MR is larger than that of the longitudinal MR. For the aged samples, the ρ(T) increase more rapidly upon cooling than that of the fresh samples. The MR of the aged samples is positive. The localization–interaction theory is examined for the observed ρ(T) and MR data of doped PA. But the model of interchain charge transfer bridged by the dopants seems to explain the negative MR as well as the metallic temperature dependence of resistivity for the perchlorate doped polyacetylene.     

Interactions of polarons in poly(3-dodecythiophene) at low temperature

Zero-field cooled-field-cooled (ZFC-FC) technique was used to investigate the effect of low temperature (4.6 K) on the interactions of polarons in weakly FeCl₃-doped poly(3-dodecylthiophene (PDDT). It was found that the magnetic properties of the system changed with the length of time system spent at low temperature: the Currie–Weiss paramagnetism gradually changed over to “antiferromagnetism” and ultimately to diamagnetism. This effect is connected with the thermochromic properties of self-organized PDDT in primary (10–15 nm) or secondary (30–50 nm) induced aggregates, in which cooling under the glass transition temperature T_g (～240 K) causes extension of the effective conjugation length of coplanar polymer chains. Changes in magnetic properties are related to the inter- and intra-chain interactions of polaron states within both the primary and secondary induced aggregates.     

Structure and magnetic behaviors of Gd6FeBi2 compound

Gd-based compounds have attracted a great deal of interest as materials with large magnetocaloric effect and as materials for spintronic applications. Fe₂P-type Gd₆FeBi₂ alloy was synthesized successfully, and the compound shows good soft magnetic behavior at room temperature with a Curie temperature ∼350 K. The compound exhibits non Curie–Weiss behavior in a large temperature range above Curie temperature, and slightly enhanced Gd moment at low temperature. The elevated Curie temperature and enhanced Gd magnetic moment were discussed based on measured electronic structure and the results from another isostructural compound Gd₆CoTe₂. The magnetocaloric effect was also measured in terms of the maximum magnetic entropy change of −4.3 J kg⁻¹ K⁻¹ at 50 kOe and −2.3 J kg⁻¹ K⁻¹ at 20 kOe, respectively.     

Magnetism and magnetocaloric effect in the ternary equiatomic REFeAl (RE = Er and Ho) compounds

Magnetic properties and magnetocaloric effect (MCE) in ErFeAl and HoFeAl intermetallic compounds have been studied systematically. Both compounds undergo a second order magnetic phase transition from paramagnetic to ferromagnetic state together with a probable spin reorientation transition at low temperature. A considerable reversible magnetocaloric effect was observed around its own Curie temperatures T_C ∼55 K and 80 K for ErFeAl and HoFeAl, respectively. For a magnetic field change of 0–7 T, the maximum values of magnetic entropy change (−ΔS_M^max) are found to be 8.3 and 9.9 J/kg K for RE = Er and Ho, respectively. The corresponding values of refrigerant capacity (RC) are evaluated to be 384 and 647 J/kg.     

X-ray absorption spectroscopy of iron-doped conducting polymers

X-ray absorption spectroscopy (XAS) measurements were performed at the Fe K edge to determine the iron local structure in chemically prepared polyaniline (PANI) and polypyrrole (PPy) samples prepared with FeCl₃ as an oxidant. The samples were conditioned at different pHs by an acid–base treatment. In both as synthesized-doped polymers, the observed dispersed Fe atoms were predominantly coordinated to chlorine as Fe(III)Cl_x species, where x=6 for PANI and x=4 for PPy samples suggesting that the polymer–counteranion bonding is weaker than the iron–chelate one. For the PANI samples submitted to basic treatment, three different sets of Fe distances were found: five Fe–O at 2.00 Å, three Fe–Fe at approximately 2.80 Å and five Fe–Fe at 3.00 Å and the near-edge spectra showed the presence of octahedrally coordinated Fe⁺³. These results strongly suggest the presence of small oxide/hydroxide aggregates. Similar data were obtained for PPy treated with NH₄OH.     

Comparison study on anticorrosion performances of the epoxy coatings with two different nano‐polyanilines for Q235 steel

Sulfuric acid doped nano‐polyaniline was prepared by direct mixed oxidation in two different systems. A novel approach for preparing polyaniline (PANI) in FeCl₂/H₂O₂ system was developed. The PANI possessed an excellent dispensability. Corrosion protection of epoxy coatings containing two kinds of polyaniline (PANI) on Q235 steel was studied by electrochemical impendance spectroscopy (EIS) technique and Tafel polarization test in 3.5 wt% sodium chloride (NaCl) aqueous solution. The results indicated that the epoxy coating containing PANI obtained in FeCl₂/H₂O₂ system had the best performance of the corrosion protection among three systems under investigation. The possible protective mechanism of PANI was discussed.     

Enhanced magnetic refrigeration capacities in minutely Co doped Mn5-xCoxGe3 compounds

Mn₅Ge₃ is a ferromagnetic compound with a Curie temperature of 299 K that exhibits a large magnetocaloric effect near room temperature. Here, we have synthesized and characterized a series of Co doped Mn_5-xCo_xGe₃ samples, in an attempt to improve the magnetocaloric properties of the system. X-ray diffraction measurements revealed that all samples exhibit the Mn₅Si₃-type D8₈ hexagonal structure at room temperature with no significant change in the lattice parameters between samples, while scanning electron micrographs showed that all samples exhibit a single compositional phase. Magnetization measurements show a decrease in Curie temperature concurrent to increasing Co concentration. Although, the magnitude of the peak magnetic entropy change stays nearly constant across the series, increased Co substitution significantly enhances the refrigerant capacity of the materials. The largest magnetocaloric effects are observed in the Mn_4.85Co_0.15Ge₃ compound with a peak magnetic entropy change of 7.58 J/kg K and a peak refrigeration capacity of 380.32 J/kg for a magnetic field change of 50 kOe.     

Large reversible magnetocaloric effect in the RECoC2 (RE=Ho and Er) compounds

The crystal structure, magnetic properties and magnetocaloric effect (MCE) of HoCoC₂ and ErCoC₂ have been investigated. They both crystallize in orthorhombic CeNiC₂-type structure with Amm2 space group and a second-order paramagnetic to ferromagnetic phase transition around the Curie temperature T_C ∼11 K and ∼14 K occurred in them. Under the magnetic field change (ΔH) of 0–5 T, the maximal values of magnetic entropy change, refrigerant capacity and relative cooling power are 15.6 J/kg K, 183 J/kg, 242 J/kg for HoCoC₂ and 17.2 J/kg K, 243 J/kg, 375 J/kg for ErCoC₂, respectively.     

Magnetic properties of Ni<Subscript>3</Subscript>Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript> alloys

Paramagnetic susceptibility of alloys Ni₃Al _x Mn_{1 − x} in the field of the transition between the ferromagnets described in the band theory (Ni₃Al) and in the spin-localized (Ni₃Mn) model of magnetic moments has been investigated. The concentration dependences of the paramagnetic Curie temperature, effective magnetic moment, and temperature-independent component of magnetic susceptibility have been determined.