Synthesis and magnetic properties of polycrystalline films of Co x Fe y Cr3 − x − y O4 and Cr2O3/CoFe2O4 multiferroics

Magnetic properties of first obtained polycrystalline films of FeCr₂O₄, CoCr₂O₄, and CoFe_0.5Cr_1.5O₄ multiferroics and films of a Cr₂O₃/CoFe₂O₄ composite multiferroic have been studied. In particular, magnetization curves and temperature dependences of the magnetic moment of the samples were measured in the temperature range 4.2–300 K in fields of up to 10 kOe. It was shown that the Curie point of a multiferroic depends on its cation composition. It was found that an exchange bias of the hysteresis loop exists in films of the Cr₂O₃/CoFe₂O₄ composite multiferroic at temperatures below the Néel point of Cr₂O₃ (330 K).     

Synthesis and magnetic properties of Ni x Fe1?x /Ni y Fe3?y O4 nanocomposite

Fe _x Ni_1−x /Ni _y Fe_3−y O₄ (0 < x, y < 1) nanocomposites were synthesized by the hydrothermal method in a rotating autoclave. The structure and magnetic properties of the composites have been investigated by Scanning electron microscopy (SEM), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The possible reaction mechanism was investigated in detail. These nanocomposites showed high special saturation magnetization Ms and relatively low coercive force Hc, which are 78.2 emu/g and 78.3 Oe, respectively.     

Hydrothermal synthesis and magnetic properties of α-MnO2 nanowires

In the present study, one-dimensional (1D) α-MnO₂ nanowires with width of 50–60 nm, length about several micrometers have been successfully prepared under hydrothermal conditions in the presence of sodium carboxymethyl cellulose. The samples were characterized by X-ray diffraction, scanning electron microscope, superconducting quantum interference device and N₂ adsorption–desorption experiment. The magnetic measurement reveals that the α-MnO₂ nanowires exhibit a ferromagnetic behavior at 5 K and a paramagnetic behavior at 300 K. The N₂ adsorption–desorption experiment shows that surface area is 160.4 m² g^?1, which is even larger than those of mesoporous nanostructures. At the same time, the possible formation mechanism for the formation of α-MnO₂ nanowires has been proposed according to the experimental results.     

Composition range and physicochemical properties of La1 − x Ba x Mn1 − y Fe y O3 solid solutions

We have determined the extent of La_{1 ? x} Ba _x Mn_{1 ? y} Fe _y O₃ solid solutions with orthorhombically and rhombohedrally distorted perovskite structures. A partial phase diagram of the LaMnO_{3 + δ}-BaMnO₃-BaFeO_2.5-LaFeO₃ system in air at a temperature of 1373 K has been proposed for the first time. We have measured the relative length change of La_{1 ? x} Ba _x Mn_{1 ? y} Fe _y O₃ samples and calculated their thermal expansion coefficients.     

The nonstoichiometry and physical properties of the Nd1−x Ca1+x FeO4−y system

The solid solutions of the Nd_1–x Ca_1+x FeO_4–y system for compositions ofx=0.000,0.125, 0.250,0.375, and 0.500 are prepared by drip pyrolysis. XRD analysis shows all the solid solutions are tetragonal I_4/mmm. The Fe⁴⁺ ratio to the total Fe ions or value has a maximum for the compositionx=0.375. From the X-ray powder diffraction analysis and the Mössbauer spectroscopy, the distortion and symmetry change of oxygen octahedra of Fe ions are observed. The structural change of oxygen octahedra of Fe ions strongly affects the physical properties. The solid solution whenx=0.000 shows a weak ferromagnetic behaviour due to the spin canting of the distorted octahedra. The other solid solutions withx=0.125, 0.250, 0.375, and 0.500 show a paramagnetic behaviour over room temperature. The decrease of the magnetic transition temperature is due to the distortion of oxygen octahedra of Fe ions and the existence of the Fe⁴⁺ ion. The formation site of oxygen vacancies plays an important role in the conductivity of the Nd_1–x Ca_1+x FeO_4–y system. Although the oxygen vacancies in [Nd, Ca]-O layer have little effect on conductivity, the oxygen vacancies in the FeO₂ plane of the perovskite layer act as electron trapping sites and thus increase the activation energy.     

Microwave-polyol controlled synthesis and magnetic properties of monodisperse CoxNi1−xFe2O4/MWCNT nanocomposites

Monodisperse Co_xNi_1−xFe₂O₄ nanoparticles (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1) with controllable composition attached on the multi-walled carbon nanotubes (MWCNTs) were prepared by microwave-polyol method. The composition of Co_xNi_1−xFe₂O₄ nanoparticles can be controlled through adjusting the atomic ratios of cobalt and nickel nitrate in the mixed solution. The influence of the microwave power and microwave irradiation time on the monodispersion of nanoparticles was also investigated. The results show quasi-spherical Co_xNi_1−xFe₂O₄ nanoparticles with the face-centered cubic structure and average crystallite size (6 nm) are uniformly dispersed on MWCNTs. The saturation magnetization of Co_xNi_1−xFe₂O₄/MWCNT nanocomposites increases gradually from 12.90 to 20.03 emu/g with increasing Co²⁺ concentration. The coercivity is almost zero at room temperature, which indicates the superparamagnetic behavior.     

Crystal structure and dielectric properties of (Pb1−x Ca x )(Zr1−y Sn y )O3 ceramics

There has been an increasing demand for dielectric resonator materials that operate in the microwave frequency range for applications in microwave communications. (Pb,Ca)ZrO₃ ceramics have a dielectric constant (_r), high quality factor (Q) and a small temperature coefficient of resonant frequency (_f). However, basic properties such as its crystal structure, temperature characteristics and the nature of its phase transformation are not yet fully understood. The temperature coefficient of resonant frequency can be controlled fairly well with the temperature coefficient of the dielectric constant. In this paper, we report the results of investigated crystal structure and the dielectric properties of (Pb_1–x Ca _x )(Zn₁– _y Sn _y )O₃ ceramics with the objective of elucidating the relationship between the crystal structure and the dielectric properties. The crystal structure refinement was performed by the Rietveld method. The dielectric properties were measured from-150–350 °C. The phase transformation was analysed from high and low temperature XRD data.     

Synthesis of Li x Na1 − x Ta y Nb1 − y O3 and LiTa y Nb1 − y O3 perovskite and pseudoilmenite solid solutions

This paper compares the solid-state reactions underlying the synthesis of LiTa _y Nb_{1 ? y} O₃ and Li _x Na_{1 ? x} Ta _y Nb_{1 ? y} O₃ solid solutions with the use of Ta_2y Nb_{2(1 ? y)}O₅ niobium tantalum pentoxides and a mechanical mixture of the Ta₂O₅ and Nb₂O₅ pentoxides. Our results demonstrate that the synthesis with the use of Ta_2y Nb_{2(1 ? y)}O₅ allows phase-pure solid solutions to be obtained at substantially lower temperatures in comparison with a mechanical mixture of Ta₂O₅ and Nb₂O₅.     

Magnetic, optical, and kinetic properties of Hg1 − x − y Mn x Dy y Te crystals

We have studied the magnetic, optical, and kinetic properties of Hg_{1 ? x ? y} Mn _x Dy _y Te crystals. The behavior of their magnetic susceptibility can be accounted for by the presence of clusters of various sizes. The Hg_{1 ? x ? y} Mn _x Dy _y Te crystals are shown to be n-type. Absorption data are used to determine the optical band gap of the crystals.     

Dielectric properties of Na1 − x K x NbO3 and Na1 − x Li x NbO3 ceramics

The dielectric properties of solid solutions based on sodium potassium and sodium lithium niobates have been studied in wide ranges of temperatures (25–750°C), frequencies (25 to 10⁶ Hz), and electric fields (up to 30 kV/cm). We have identified solid-solution regions differing in the temperature and frequency dependences of the dielectric permittivity. It is reasonable to take into account the present results in device applications where wide variations in dc bias field and frequency are needed.     

Controlled synthesis and magnetic properties of Co1−xNix/MWCNT nanocomposites by microwave irradiation

Co_1?xNi_x alloy nanoparticles (x = 0.2, 0.5, 0.6, and 0.8) with the diameter 15–28 nm attached on the surface of multi-walled carbon nanotubes (MWCNTs) were prepared to form Co_1?xNi_x/MWCNT nanocomposites by microwave irradiation. Experimental results demonstrated that Co_1?xNi_x alloy nanoparticles with quasi-spherical and face-centered cubic structure had been attached on the MWCNTs, the composition and size of Co_1?xNi_x alloy nanoparticles could be controlled through adjusting the atomic ratios of metal Co to Ni in the mixed acetate solution, the microwave power and microwave irradiation time, respectively. Both the coercivity and the saturation magnetization of Co_1?xNi_x alloy nanoparticles increased with increasing Co concentration from x = 0.8 to 0.5, and decreased when Co concentration was increased from x = 0.5 to 0.2. These confirm that microwave synthesis is promising for fabricating alloy nanoparticles attached on MWCNTs for magnetic storage and ultra high-density magnetic recording applications.     

High temperature mechanical properties of La1−x Sr x Cr1−y Co y O3 for SOFC interconnect

Solid oxide fuel cells (SOFC) require an interconnect for fabrication into stacked cells. This is typically La(Sr, Ca)CrO₃, of which much data on the electrical and physical properties already exists. However, very little information exists on the high temperature mechanical properties of the material, which is a necessity for future design improvements. La_1–x Sr _x Cr_1–y Co _y O₃ samples were fabricated into green dry-pressed bars and pellets, and sintered under various heating and cooling regimes. The sinterability and high temperature mechanical properties of the material was then investigated as a function of the dopant concentration. It was observed, for example, that the modulus of rupture of the dry pressed La_0.7Sr_0.3Cr_1–yCo_yO₃ (y 0.3) gave a value of over 110 MPa at 1000 °C. This paper will provide data on the high temperature mechanical properties of the material and its application to the SOFC system.     

First-principles investigations of structural, elastic, electronic and magnetic properties of Ga1−x Mn x P and In1−x Mn x P

We employ the full-potential linearized augmented plane wave plus local orbital (FP L/APW + lo) method based on the density functional theory (DFT) in order to investigate the structural, elastic, electronic, and magnetic properties of ordered dilute ferromagnetic semiconductors Ga_1?x Mn _x P and In_1?x Mn _x P at (x = 0.25) in the zinc blende phase, using generalized gradient approximation, GGA (PBE). To our knowledge the elastic constants of these compounds have not yet been measured or calculated, hence our results serve as a first quantitative theoretical prediction for future study. Results of calculated electronic structures and magnetic properties reveal that both Ga_0.75Mn_0.25P and In_0.75Mn_0.25P have stable ferromagnetic ground state, and they are ideal half-metallic (HM) ferromagnetic at their equilibrium lattice constants. Also we show the nature of the bonding from the charge spin-densities calculations. The calculated total magnetic moments are 4.0 μ_B per unit cell for both Ga_0.75Mn_0.25P and In_0.75Mn_0.25P, which agree with the Slater–Pauling rule quite well, and we observe that p–d hybridization reduces the local magnetic moment of Mn from its free space charge value and produces smaller local magnetic moments on the nonmagnetic Ga, In and P sites. The values of N ₀α and N ₀β exchange constants confirm the magnetic nature of these compounds. From the robust half-metallicity of Ga_0.75Mn_0.25P and In_0.75Mn_0.25P as a function of lattice constant is also investigated.     

Growth and properties of Ga y In1 − y P z As1 − x − z Bi x solid solutions on GaP substrates

Data are presented on temperature-gradient melt growth of GaInPAsBi solid solutions on GaP substrates. Heterophase equilibria in the Ga-In-P-As-Bi system are analyzed in terms of the regular solution model. The growth kinetics, composition, and structural perfection of GaInPAsBi/GaP heterostructures are investigated.     

Crystal structure and magnetic properties of Sr1 − x Sm x Fe12 − x Co x O19 solid solutions

Sr_{1 ? x} Sm _x Fe_{12 ? x} Co _x O₁₉ (0 ≤ x ≤ 0.5) ferrites have been prepared by solid-state reactions in air at 1470 K using mixtures of samarium oxide, ferric oxide, Co₃O₄, and strontium carbonate. X-ray diffraction characterization showed that the samples with x < 0.2 were single-phase, whereas the samples with 0.2 ≤ x ≤ 0.5 contained α-Fe₂O₃ and those with 0.3 ≤ x ≤ 0.5 contained SmFeO₃, CoFe₂O₄, and Sm₂O₃ as well. The highest degree of Sm³⁺ and Co²⁺ substitutions for Sr²⁺ and Fe³⁺ (x) in the SrFe₁₂O₁₉ ferrite at 1470 K was determined to be slightly less than 0.2. This substitution only slightly decreases the a and c parameters of the hexagonal lattice and the Curie temperature (T _C) of the material. At temperatures of 5 and 300 K in magnetic fields of up to 14 T, we obtained magnetic hysteresis loops, which were used to evaluate the spontaneous magnetization (σ₀), specific saturation magnetization (σ_s), and coercive force (_σ H _c) of the ferrites. The experimentally determined 5-K spontaneous magnetization per formula unit (n ₀) of the x = 0.1 ferrite is 20.86μ_B, which coincides with the theoretical value calculated as n ₀ = (8 × 5) ? (3.9 × 5 ? 0.1 × 3) = 20.8μ_B. At 300 K, the n ₀ and _σ H _c of Sr_0.9Sm_0.1Fe_11.9Co_0.1O₁₉ exceed those of SrFe₁₂O₁₉ by 7.7 and 9.9%, respectively.     

Transport Properties of Heavy Fermion Compounds: YbIn1−x Cu4+x and YbIn1−y Ag y Cu4

The intermetallic compounds of Yb with In and Cu (YbIn_1–x Cu_4+x ) and Yb with In, Ag, and Cu (YbIn_1–y Ag _y Cu₄) exhibit interesting magnetic and transport properties. Of the compounds of Yb with In and Cu the compound with x=0, namely YbInCu₄, has attracted particular attention, because—while being a Curie–Weiss paramagnet—it undergoes a first-order isostructural phase transition at T _v =approx. 40 to 80 K and atmospheric pressure. Below T _v the ytterbium in this compound is in a mixed-valence state and the compound as a whole is sometimes called a light heavy-fermion system. Above T _v , the compound is known as a Curie–Weiss paramagnet of localized magnetic moments and, below T _v , a Pauli paramagnet in a nonmagnetic Fermi-liquid state. In the present paper the results of measurements of the thermal conductivity of polycrystalline samples, YbIn_1–x Cu_4+x with x=0,0.015, 0.095, and 0.17 and YbIn_1–y Ag _y Cu₄ with y=0, 0.3, 0.7, and 1.0, are reported. The thermal conductivity is separated into the phonon thermal conductivity ( _ph ) (i.e., related to the heat carried by phonons) and into the electronic thermal conductivity ( _e ) (related to the heat carried by electrons). The electrical resistivity of the compounds was measured to determine the temperature dependence of the Lorenz number. The results show that in the temperature interval 4.2 to 300 K the latter quantity behavior follows the theoretical predictions for heavy fermion materials.