Crystal structural, magnetic and electrical transport properties of CeKFeMoO6 double perovskite

The crystal structural, magnetic and electrical transport properties of double perovskite CeKFeMoO₆ have been investigated. The crystal structure of the compound is assigned to the monoclinic system with space group P2₁/n and its lattice parameters are a=0.55345(3) nm, b=0.56068(2) nm, c=0.78390(1) nm, β=89.874(2). The divergence between zero-field-cooling and field-cooling M-T curves demonstrates the anisotropic behavior. The Curie temperature measured from C_p-T curve is about 340 K. Isothermal magnetization curve shows that the saturation and spontaneous magnetization are 1.90 and 1.43 μ_B/f.u. at 300 K, respectively. The electrical behavior of the sample shows a semiconductor. The electrical transport behavior can be described by variable range hopping model. Large magnetoresistance, −0.88 and −0.18, can be observed under low magnetic field, 0.5 T, at low and room temperature, respectively.     

Structural,electronic and magnetic properties of the double perovskite Pb2FeReO6

The structural, electronic and magnetic properties of the double perovskite Pb₂FeReO₆ have been studied by using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA) as well as taking into account the on-site Coulomb repulsive and exchange coupling interactions (GGA+U). The optimized crystal structure of the Pb₂FeReO₆ is a body-centered tetragonal (BCT) with a space group of I4/m and the lattice constants of a=b=5.59 Å and c=7.93 Å, consistent with the experimental results. The two axial transition metal and oxygen (TM–O) distances are slightly larger than the four equatorial TM–O distances and shows the existence of the Jahn–Teller structural distortion in FeO₆ and ReO₆ octahedra. The Fe³⁺ and Re⁵⁺ ions are in the states (3d⁵, S=5/2) and (5d², S=1) with magnetic moments 3.929 and −0.831μ_B respectively and thus antiferromagnetic (AFM) coupling via oxygen between them. The half-metallic (HM) ferromagnetic (FM) nature implies a potential application of this new compound in magnetoelectronic and spintronics devices.     

Effect of Cd on the structural, magnetic and electrical properties of nanostructured Mn-Zn ferrite

Nanoparticles of Mn_0.5Zn_0.5−xCd_xFe₂O₄ (x=0.0, 0.1, 0.2 and 0.3) have been synthesized by a chemical co-precipitation method. The lattice constant increases with increasing Cd content. X-ray calculations indicate that there is deviation in the cation distribution in the nanostructured spinel ferrite. The dielectric constant and dielectric loss decrease for the samples with Cd content up to x=0.2. However the dielectric constant rises for x=0.3. This is due to an increase in the hopping process at the octahedral (B sites). The dielectric constant increases with increase in temperature, indicating a thermally activated hopping process. The DC resistivity increases with Cd content up to x=0.2 and decreases for Cd content x=0.3. The maximum magnetization of all the samples decreases with increase in Cd content.     

Structural phase transitions at high-temperature in double perovskite Sr2GdRuO6

The crystal structure evolution of the Sr₂GdRuO₆ complex perovskite at high-temperature has been investigated over a wide temperature range between 298 K≤T≤1273 K. Powder X-ray diffraction measurements at room temperature and Rietveld analysis show that this compounds crystallizes in a monoclinic perovskite-type structure with P2₁/n (#14) space group and the 1:1 ordered arrangement of Ru⁵⁺ and Gd³⁺ cations over the six-coordinate M sites, with lattice parameters a=5.81032(8) Å, b=5.82341(4) Å, c=8.21939(7) Å, V=278.11(6) Å³ and angle β=90.311(2)^o. The high-temperature analysis shows that this material suffers two-phase transitions. At 373 K it adopts a monoclinic perovskite structure with I2/m space group, and lattice parameters a=5.81383(2) Å, b=5.82526(4) Å, c=8.22486(1) Å, V=278.56(2) Å³ and angle β=90.28(2)^o. Above of 773 K, it suffers a phase transition from monoclinic I2/m to tetragonal I4/m, with lattice parameters a=5.84779(1) Å, c=8.27261(1) Å, V=282.89(5) Å³ and angle β=90.02(9)^o. The high-temperature phase transition from monoclinic I2/m to tetragonal I4/m is characterized by strongly anisotropic displacements of the anions.     

Effect of Gd doping on structural, electrical and magnetic properties of BiFeO3 electroceramic

Room temperature multiferroic electroceramics of Gd doped BiFeO₃ monophasic materials have been synthesized adopting a slow step sintering schedule. Incorporation of Gd nucleates the development of orthorhombic grain growth habit without the appearance of any significant impurity phases with respect to original rhombohedral (R3c) phase of un-doped BiFeO₃. It is observed that, the materials showed room temperature enhanced electric polarization as well as ferromagnetism when rare earth ions like Gd doping is critically optimized (x=0.15) in the composition formula of Bi_1+2xGd_2x/2Fe_1−2xO₃. We believe that magnetic moment of Gd⁺³ ions in Gd doped BiFeO₃ tends to align in the same direction with respect to ferromagnetic component associated with the iron sub lattice. The dielectric constant as well as loss factor shows strong dispersion at lower frequencies and the value of leakage current is greatly suppressed with the increase in concentration of x in the above composition. Addition of excess bismuth and Gd (x=0.1 and 0.15) caused structural transformation as well as compensated bismuth loss during high temperature sintering. Doping of Gd in BiFeO₃ also suppresses spiral spin modulation structure, which can change Fe-O-Fe bond angle or spin order resulting in enhanced ferromagnetic property.     

Orbital-decomposed electronic and magnetic properties of the double perovskite Sr2FeReO6

The detailed orbital-decomposed electronic structures and magnetic properties of the double perovskite Sr₂FeReO₆ have been studied using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA). Both occupied and unoccupied s and three p states of Fe³⁺ ion are located far away from the Fermi level, while all up-spin states and most down-spin states are completely filled for the s and three p states of Re⁵⁺ ion. The octahedral crystal field of the oxygen atoms around transition-metal (TM) sites splits the five-fold degenerate d states of the free TM atoms into triply degenerate t_2g states with smaller bonding-antibonding splitting and doubly degenerate e_g states with larger bonding-antibonding splitting. The Fe³⁺ and Re⁵⁺ ions are in the states (3d⁵, S=5/2) and (5d², S=1) with magnetic moments 3.70 and −0.86μ_B, respectively and thus antiferromagnetic coupling via oxygen between them. There are no direct interactions between two nearest Fe-Fe or Re-Re pairs, whereas along each Fe-O-Re-O-Fe or Re-O-Fe-O-Re chains, the hybridizations between Fe 3d and 4s, O 2s and 2p, as well as Re 5p, 5d and 6s orbitals are fairly significant.     

Structural, microstructural and magnetic properties of NiFe2O4, CoFe2O4 and MnFe2O4 nanoferrite thin films

The structural, microstructural and magnetic properties of nanoferrite NiFe₂O₄ (NF), CoFe₂O₄ (CF) and MnFe₂O₄ (MF) thin films have been studied. The coating solution of these ferrite films was prepared by a chemical synthesis route called sol-gel combined metallo-organic decomposition method. The solution was coated on Si substrate by spin coating and annealed at 700 °C for 3 h. X-ray diffraction pattern has been used to analyze the phase structure and lattice parameters. The scanning electron microscopy (SEM) and atomic force microscopy (AFM) have been used to show the nanostructural behavior of these ferrites. The values of average grain's size from SEM are 44, 60 and 74 nm, and from AFM are 46, 61 and 75 nm, respectively, measured for NF, CF and MF ferrites. At room temperature, the values of saturation magnetization, M_s∼50.60, 33.52 and 5.40 emu/cc, and remanent magnetization, M_r∼14.33, 15.50 and 1.10 emu/cc, respectively, are observed for NF, CF and MF. At low temperature measurements of 10 K, the anisotropy of ferromagnetism is observed in these ferrite films. The superparamagnetic/paramagnetic behavior is also confirmed by χ′(T) curves of AC susceptibility by applying DC magnetizing field of 3 Oe. The temperature dependent magnetization measurements show the magnetic phase transition temperature.     

空穴掺杂Sr2FeMoO6的晶体结构及磁性研究

采用传统高温固相反应法制备了空穴掺杂的系列样品Sr2xKxFeMoO6（0≤x≤0．04）,研究了其晶体结构和磁性质．X射线粉末衍射结果表明该系列样品均为单相,四方晶系,空间群为I4／m．碱金属K的含量可以调控反位缺陷的浓度．未掺杂样品Sr2FeM006在280K时的原胞磁矩为1．12μB．掺杂量为x=0．04样品的原胞磁矩为1．26μB．阳离子有序、晶格畸变是影响Sr2-xKxFeMoO6磁性的重要因素．     

Reflux synthesis of Co3O4 nanoparticles and its magnetic characterization

Co₃O₄ nanoparticles have been prepared for the first time via reflux method, as an alternative low-temperature high-yield process, starting from one single precursor. A plausible mechanism is suggested for the synthetic process. XRD, TEM, FTIR and VSM were used for the structural, morphological, spectroscopic, and magnetic characterization of the product respectively. X-ray diffraction line profile fitting showed that average particle size of the sample is 28 nm. Morphology of the synthesized powder was observed to be thin nanosheets with a thickness of 2-3 nm based on SEM and TEM analyses. Magnetic measurements showed a deviation of the Neel temperature from the bulk value which is attributed to the finite size effects. A loop shift with an enhanced coercivity is observed in the field-cooled hysteresis loops. The opening of the hysteresis loop reveals the existence of the spin-glass like surface spins of the Co₃O₄ nanoparticles.     

Effect of cation distribution on the structural and magnetic properties of nickel substituted nanosized Mn–Zn ferrites prepared by co-precipitation method

Nano particles of Mn_(0.5–x)Ni_xZn_0.5Fe₂O₄ (x=0.0, 0.1, 0.2, 0.3) have been synthesized by chemical co-precipitation method. The lattice constant and distribution of cation in the tetrahedral and octahedral sites have been deduced through X-ray diffraction (XRD) data analysis. The lattice constant (Å) for all Mn/Ni concentration is found to be less than that for the corresponding bulk values. X-ray intensity calculations indicate that there is deviation in the normal cation distribution. Magnetization decreases with increasing Ni concentration except for x=0.3, where it shows increasing trend. This is due to migration of Fe³⁺ ions from B-site to A-site, which reduces the B–B coupling and there by the spin canting in the B sublattice. The Curie temperature was found to decrease with increase in nickel concentration except for x=0.3, where it shows a rise. Coercivity is very low and is found to be inversely proportional to the grain size.     

Preparation and characterization of NiFe2O4/NiO composite film via a single-source precursor route

NiFe₂O₄/NiO nanocomposite thin films have been successfully prepared through a facile route using nickel iron layered double hydroxide (NiFe-LDH) as a single-source precursor. This synthetic approach mainly involves the formation of NiFe-LDH film by casting the slurry of NiFe-LDH precursor on the α-Al₂O₃ substrate, followed by high-temperature calcination. The composition, microstructure and properties of the films were characterized in detail by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and vibrating sample magnetometer (VSM). The results indicate that NiFe₂O₄/NiO composite film was composed of granules with diameter less than 100 nm, and the thickness of the film was in the range 1-2 μm. The magnetization of the film can be tuned by alternating the Ni/Fe molar ratio of LDH precursor. In addition, the method developed should be easily extended to fabricate other MFe₂O₄/MO composite film systems with specific applications just by an appropriate combination of divalent/trivalent composition in the precursor of LDHs.     

New ferromagnetic La3Co2TaO9 double perovskite: Structural and magnetic properties

The new double perovskite La₃Co₂TaO₉ has been prepared by a solid-state procedure. The crystal and magnetic structures have been studied from X-ray powder diffraction (XRPD) and neutron powder diffraction (NPD) data. Rietveld refinements were performed in the monoclinic space group P2₁/n. The structure consists of an ordered array of alternating B′O₆ and B″O₆ octahedra sharing corners, tilted along the three pseudocubic axes according to the Glazer notation a⁻b⁻c⁺. Rietveld refinements show that at RT the cell parameters are a=5.6005(7) Å, b=5.6931(7) Å, c=7.9429(9) Å and β=89.9539(7)°, and the refined crystallographic formula of this “double perovskite” can be written as La₂(Co)_2d(Co_1/3Ta_2/3)_2cO₆. Magnetization measurements and low-temperature NPD data show that the perovskite is a ferromagnet with T_C=72 K. At high T it follows the Curie–Weiss law with an effective magnetic moment of 3.82μ_B per Co ion which is very close to spin only Co²⁺ (HS).     

A novel method to synthesize LiVPO4F/C composite materials and its electrochemical Li-intercalation performances

Triclinic LiVPO₄F/C composite materials were prepared from a sucrose-containing precursor by one-step heat treatment. As-prepared composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical measurements. XRD studies showed that Li₃PO₄ impurity phase appeared in the sample synthesized at 600 °C and pure LiVPO₄F samples could be obtained when the sintered temperature was higher than 650 °C. The sample synthesized at 650 °C presents the highest initial discharge capacity of 132 mAh g⁻¹ at 0.2 C rate, and exhibited better cycling stability (124 mAh g⁻¹ at 50th cycle at 0.2 C rate) and better rate capability (100 mAh g⁻¹ at 50th cycle under 1 C rate) in the voltage range 3.0-4.4 V.     

High pressure investigation on double perovskite Ba2MgWO6

The results of high-pressure angle dispersive X-ray diffraction measurements up to 34.3 GPa on the double perovskite Ba₂MgWO₆ are presented. The ambient rock salt phase (SG: Fm-3m) is found to be stable up to the highest pressure of the present measurements. The third order Birch-Murnaghan equation of state when fitted to pressure-volume data, yielded a zero pressure bulk modulus (B₀),and its first and second pressure derivatives as 137.0(81) GPa, and 3.9(5) and −0.03 GPa⁻¹, respectively.     

Influence of Co, Ni and Zn substitution for Cu on the structural and superconducting properties of (Hg0.7Cr0.3)Sr2CuO4+δ

The effect of Co, Ni and Zn substitutions for Cu on the phase stability and superconducting properties of (Hg_0.7Cr_0.3)Sr₂CuO_4+δ was investigated. X-ray diffraction (XRD) revealed that both Co and Zn are soluble in the (Hg_0.7Cr_0.3)Sr₂CuO_4+δ material up to about 5% of the Cu content, whereas the solubility of Ni is extended up to 10%. Electrical resistivity and magnetic susceptibility measurements show that the value of the superconducting critical temperature T_c decreases linearly with the impurity content. The depression of T_c indicates that the suppression of the superconductivity in Co- and Ni-substituted samples is much stronger than that in Zn-substituted ones. The residual resistivity scales linearly with the doping level as expected from the impurity scattering due to disorder. Some possible explanations for the stronger suppression of T_c by the Co and Ni substitution than by Zn substitution are provided.     

Synthesis, crystal structure, dielectric and optical properties of a new rare earth double perovskite: Ca2CeNbO6

In order to develope and understand the phenomena involved in producing advanced materials, a rare earth double perovskite oxide calcium cerium niobate, Ca₂CeNbO₆ (CCN) is synthesized for the first time. The x-ray diffraction pattern of CCN at room temperature (300K) shows orthorhombic perovskite structure, with the lattice parameters, a=9.36Å, b=6.61Å and c=5.88Å and α=β=γ= 90°. A scanning electron micrograph shows the formation of grains with average size ∼2μm. Impedance spectroscopy and Fourier transform infrared spectroscopy are applied to investigate the dielectric and optical properties of CCN. The frequency-dependent electrical data are analyzed in the framework of the conductivity and modulus formalisms. The experimental data of real part of dielectric permittivity (ε′) and imaginary part of electric modulus (M″) are fitted with Davidson-Cole equation to explore the idea of dielectric relaxation (conduction) mechanism in CCN. The frequency-dependent conductivity spectra follow a power law. The scaling behaviour of imaginary electric modulus (M″) suggests that the relaxation describes the same mechanism at various temperatures.     

Effect of Mo doping on magnetic and transport properties of La0.5Sr0.5CoO3

The substitutional effect of Mo on the magnetic and transport properties of double exchange ferromagnets, La_0.5Sr_0.5Co_1−x Mo_xO₃ (0?x?0.2) has been investigated. Substitution of 10% Mo at the Co-site of La_0.5Sr_0.5CoO₃ decreases the Curie temperature by ∼60 K than that of the parent compound and the long-range ferromagnetic ordering disappears for x?0.2. The Mo-doped samples, however, undergo a transition from the parent metallic state to the insulating state below T_c. The insulating state is found to obey Mott's variable range hopping of conduction. The effect of Mo substitution is attributed to the factors namely, (i) the dilution of magnetic Co sublattice, (ii) the reduction of Co⁴⁺/Co³⁺ ratio resulting in a reduced carrier concentration and (iii) disruption of the intermediate spin structure of Co, namely Co³⁺: t_2g⁵e_g¹.     

Synthesis,magnetic and electrical transport properties of magnetoresistance material Sr2FeMoO6 by microwave sintering

Magnetoresistance material Sr₂FeMoO₆ with double perovskite structure was synthesized by microwave sintering method using SrCO₃, Fe₂O₃ and MoO₃ as raw materials, with MnO₂ for microwave absorber. The phase structure, magnetic and electrical transport properties were investigated by X-ray powder diffraction (XRD) and vibrating-sample magnetometer. XRD analysis shows that the as-synthesized sample is Sr₂FeMoO₆ with tetragonal crystal structure and I4/mmm space group. The unit cell parameters are a=0.5587 nm, c=0.7894 nm, volume=0.2464 nm³. The calculated grain size of the sample is 31.62 nm, which is obtained by the Scherrer formula using the diffraction data. Magnetism testing results show that the sample Sr₂FeMoO₆ is ferromagnetic with the magnetic transition temperature of about 380 K. Under 1.0 T magnetic field, the saturation and spontaneous magnetization of Sr₂FeMoO₆ is 1.25 μ_B/f.u. and 1.00 μ_B/f.u. at room temperature. The magnetoresistance ratio of the sample is 28%. Electrical transport properties testing results indicate that the sample exhibits typical semiconductor behavior. The conductive mechanism of Sr₂FeMoO₆ is highly dependent on temperature: within the temperature range of 100–300 K, the mechanism is attributed to the small polaron variable-range hopping model; while it is ascribed to the adiabatic small polaron model within the temperature range of 80–100 K.     

Electronic transport and magnetic studies of La1−xCax−0.08Sr0.04Ba0.04MnO3

Lanthanum based mixed valence manganite system La_1−xCa_x−0.08Sr_0.04Ba_0.04MnO₃ (LCSBMO; x=0.15, 0.24 and 0.33) synthesized through the sol-gel route is systematically investigated in this paper. The electronic transport and magnetic susceptibility properties are analyzed and compared, apart from the study of unit cell structure, microstructure and composition. Second order phase transition is observed in all the samples and significant difference is observed between the insulator to metal transition temperature (T_MI) and paramagnetic (PM) to ferromagnetic (FM) transition temperature (T_C). In contrast to the insulating FM behaviour usually observed in La_1−xCa_xMnO₃ (LCMO) for x=0.15, a clear insulator to metal transition is observed for LCSBMO for the same percentage of lanthanum. The temperature dependent resistivity of polycrystalline pellets, when obeying the well studied law ρ=ρ_o+ρ₂T² for T<T_MI, is observed to differ significantly in the values of ρ_o and ρ₂, with the electrical conductivity increasing with x. The variable range hopping model has been found to fit resistivity data better than the small polaron model for T>T_MI. AC magnetic susceptibility study of the polycrystalline powders of the manganite system shows the highest PM to FM transition of 285 K for x=0.33.