Electrical and magnetic properties of double perovskite: Y2CoMnO6

In this communication, the structural, micro-structural, dielectric, electrical, magnetic, and leakage-current characteristics of a double perovskite (Y₂CoMnO₆) ceramic material have been reported. The material was synthesized via a high-temperature mixed-oxide route. The compound crystallizes in a monoclinic structure which is confirmed from preliminary X-ray structural study. The morphological study by using scanning electron micrograph reveals the almost homogeneous distribution of grains throughout the surface of the sample. The nature of frequency-dependence of dielectric constant has been described by the Maxwell-Wagner model. The occurrence of a dielectric anomaly in the temperature dependence of dielectric permittivity study demonstrates the ferroelectric-paraelectric phase transition in the material. From the Nyquist plots, we found the existence of both grain and grain boundary effects. The frequency dependence of conductivity was studied by the Jonscher’s Power law, and the conduction phenomenon obeys the large overlapping polaron tunneling model. By using the Arrhenius equation, the activation energy has been calculated which is nearly equal to the energy required for the hoping of the electron. Both impedance and conductivity analysis demonstrate that the sample exhibits negative temperature coefficient of resistance (NTCR) properties indicating the semiconducting type of material at high temperatures. The anti-ferromagnetic character of the material is observed from the nature of magnetic hysteresis loop. The leakage current analysis suggests that the conduction process in the material follows the space charge limited conduction phenomenon. Such material will be helpful for modern electronic devices and spintronic applications.     

Examples of high-resolution electron microscopy (HREM) investigation of complex oxides related to perovskite

The properties of oxides may be drastically influenced by their microstructures. Thus the knowledge of nonstoichiometric mechanisms is an essential tool for the conception of new inorganic compounds by solid-state chemist. Through three chosen examples of complex oxides with perovskite-related structure, these points are illustrated. The new families of phosphate tungsten bronzes, the antiferromagnetic AMn_{1 ? x} Fe_xO_{3 – y}, and the copper oxides LCuO_{3 – x} (La = Ba, Y, La) were studied by high-resolution electron microscopy (HREM) in order to analyze the mechanisms of nonstoichiometry, the defects of which can modify their physical properties (magnetism or electronic conductivity) and the factors that govern their stabilization.     

NMR Spin-Lattice Relaxation Rates in Cuprates

An analysis of nuclear spin-lattice relaxation data in the normal state of cuprates that appropriately accounts for the highly anisotropic structures shows no contrasting temperature dependence of the Cu, O, and Y relaxations, which suggests that all nuclei relax by the same mechanism of the spin liquid. To investigate the temperature dependence of this mechanism, the model of fluctuating fields is used in which the rates are expressed in terms of hyperfine interaction energies and an effective correlation time τ _eff characterizing the dynamics of the spin fluid. The former contain the effects of the antiferromagnetic static spin correlations, which cause the hyperfine field constants to be added more coherently at low temperature but incoherently at high temperature. At low temperatures, τ _eff grows linearly with temperature as in ordinary metals. At high temperatures, however, the nuclear spin-lattice relaxation rates in various cuprates unequivocally reflect local moment features. This behavior is similar to that observed for the magnetic transition metals Fe, Co, and Ni, where also some properties show a cross-over from an itinerant behavior of delocalized electrons at low to that of localized moments at high temperatures.     

Crystallographic and physical properties of new ternary R2T3X9 (R=La, Ce, U, T=Rh, Ir, X=Al, Ga) compounds

Ternary compounds with the stoichiometry R₂T₃X₉ (R=La, Ce, U, T=Rh, Ir, X=Al, Ga) were synthesized for the first time and were found to crystallize in the orthorhombic Y₂Co₃Ga₉-type structure. Preliminary measurements of the resistivity, the susceptibility, the specific heat, and the Seebeck coefficient revealed a rather unconventional behavior for the Ce-compounds, which exhibit characteristics of both intermediate valent and of heavy fermion compounds. The U counterparts were found to order antiferromagnetically at temperatures below 40 K.     

Hydrothermal synthesis and characterization of a new layered compound Li2VGeO5

The new compound Li₂VGeO₅ with a layered structure has been synthesized at 580 °C via the hydrothermal method. The compound crystallizes in the space group P4/n of the tetragonal system with two formula units in a cell of dimensions a=6.5187(9) Å, c=4.5092(9) Å (T=298 K), V=191.61(5) Å³. The structure is composed of layers made of repeating [(VO₅)(GeO₄)]¹⁻ units. Li⁺ ions reside between the layers. The magnetic susceptibility data show an antiferromagnetic coupling below 5 K with C=0.47 emu K mol⁻¹, and θ=−13 K with μ_eff=1.89μ_B for each Li₂VGeO₅ unit.     

On the magnetic ordering of R6Fe13X compounds

Neutron diffraction performed on Pr₆Fe₁₃Ag and Pr₆Fe₁₃Au powder samples reveals a collinear antiferromagnetic ordering of the four Fe and the two Pr sublattices associated with the wave vector q=(001) (I_P magnetic lattice with anticentering translation). The moments of all sublattices located at (xy0) layers, sandwiched between successive X layers perpendicular to z at z=−0.25, 0.25, are confined to the same direction within the (xy0) plane. They change their direction collectively when going to the next Ag(Au) layers at z=0.25, 0.75. The Pr moments at 1.5 K are 2.5(2)μ_B and 2.6(1)μ_B/Pr atom, while the average Fe ordered value is 2.2μ_B/Fe atom, in agreement with Mössbauer results. Detailed results are presented for Pr₆Fe₁₃Ag.     

Role of polarons in the antiferromagnetic behaviour of poly (3-dodecylthiophene)

A mathematical model was suggested and tested to elucidate the antiferromagnetic behaviour of temperature dependence of the magnetic susceptibility of poly(3-dodecylthiophene) (PDDT) which takes advantage of the physical properties of polarons and bipolarons. It has been found that the responsibility for the antiferromagnetic behaviour of temperature dependence of the magnetic susceptibility of PDDT is the conversion of polarons to bipolarons, rather than the presence of several crystalline sublattices of the polymer with different orientations of magnetic moments. The antiferromagnetic character is caused by paramagnetic polarons, the number of which decreases with lowering temperature. The proposed model was verified, with good results also for other conductive polymers exhibiting antiferromagnetic properties known from the literature.     

Green synthesis of hematite (α-Fe2O3) submicron particles

Iron oxide microparticles have been synthesized through a green technique using hydrogen peroxide under sunlight irradiation. The X-ray powder diffraction measurement shows that these particles are hematite (α-Fe₂O₃). The microstructure and particle size were investigated using scanning electron microscopy. The magnetic characterization shows the presence of Morin transition at about 258 K, which is very close to the normal value (263 K) of bulk hematite. These hematite particles show typical antiferromagnetic behavior at low temperature and weak ferromagnetic behavior at room temperature.     

Physical and magnetic properties of iron oxide nanoparticles with a different molar ratio of ferrous and ferric

The magnetite (Fe₃O₄) nanoparticles were synthesized with the same reaction conditions like co-precipitation method, molar ratio, and raw materials, but their magnetization values were not the same. This due to the change of some properties of ferrous oxide (Fs) nanoparticles when exposed it to the air. So this work suggested the core-shell design of magnetite nanoparticles (MA), this core-shell was prepared from ferric oxide (Fc) nanoparticles coated with sheets from ferrous oxides (Fs). The magnetic properties of iron oxide nanoparticles with different molar ratios of ferrous and ferric were studied via co-precipitation with NaOH. The crystallographic and phase structure of prepared iron oxides nanoparticles were investigated by employing Wide angle X-ray diffraction (WAXD), Particle size and zeta potential, Vibrating Sample Magnetometer (VSM), X-ray fluorescence (XRF), Fourier transforms infrared spectroscopy (FTIR) and High resolution transmission electron microscopy (HR-TEM). The changed magnetic moment of iron oxide nanoparticles was attributed to the presence of different a concentration of manganese atoms.     

A first report of the complexes of 5,11,17,23-tetra-tert-butyl-25,27-diethoxycarboxymethoxy-26,28-dihydroxycalix[4]arene with Mn(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II)

Totally six dinuclear complexes of Mn(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) of calix[4]arene derivatized with two pendants possessing terminal –COOH functions at two of its alternate phenolic –OH groups were synthesized for the first time and were well characterized.