Bohr Magneton Number Research Articles

Influence of Ni substitution on Structural, Optical, magnetic and transport properties of Mn0.5-xNixZn0.4Cu0.1Fe1.95Al0.05O4

A series of spinel ferrites Mn0.5-xNixZn0.4Cu0.1Fe1.95Al0.05O4 have been prepared by auto-combustion technique. X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) have been used for structural and morphological investigations. The XRD patterns confirm the formation of cubic spinel structure of ferrites. The lattice constants decrease with the increase of Ni contents due to the smaller ionic radii of Ni2+ compared to Mn2+ as well as particle size decreases. Density is increased and porosity is decreased with the increase of Ni contents in the samples due to the higher atomic weight of Ni2+ compared to Mn2+. The FESEM analysis reveal that the average size of the irregularly shaped grains increased with Ni contents. The mixed spinel structure is further confirmed by the FTIR spectra, which show a doublet band at about 600 cm−1. The observed optical band gap and the particle size variations are comparable, and the quantum size effect supports this conclusion. The real part of initial permeability and relative quality factor increase with the increase of Ni contents due to increase of density and grain size as well as decrease of porosity. Also, it is found that magnetic loss decreased with the increase of Ni contents. All the samples exhibit ferrimagnetic behavior and the number of Bohr magneton has been calculated for all compositions. The dielectric constant shows large value in the lower frequencies and decreases with frequency shows dispersion due to Maxwell-Wagner space charge polarization. The investigation of electric modulus has demonstrated the existence of the hopping conduction mechanism. The AC conductivity is very low at lower frequency region and very large at higher frequency region which can be explain according to the polaron hopping model of Austin and Mott. The AC conductivity enhances nearly linearly with frequency, suggesting that the mechanism of conduction is due to small polaron hopping, which can be described according to Jonscher’s power law. Also, the effect of grain and grain boundary resistance on transport properties has been investigated using complex impedance analysis and it has been observed that both exhibit an increase trend as the Ni content increases.

Magnetic Behaviour, and initial permeability of green synthesized Co2+ substituted Ni-Zn ferrite

This study investigates the magnetic properties of Ni0.55−xZn0.45CoxFe2O4 (x = 0.0, 0.15, 0.25, 0.35, 0.45, 0.55) ferrite nanoparticles synthesized via the green synthesis route using orange juice as a green reductant. The magnetocrystalline anisotropy constant (Ms) and the Bohr magneton number (nB) of the Ni-Zn ferrites increase linearly with an increase in the content of Co2+ ions. The magnetic properties such as Saturation magnetization, Coercive force, and remanence ratio (Mr / Ms) are determined. The Curie temperature for the studied ferrites is found to be reduced upon doping with cobalt ions and is considered as the weakening of the A-B exchange interaction.

Effect of thermobaric treatment on magnetic and superconductive properties of HPHT-grown nitrogen-doped diamond crystals

The effect of thermobaric treatment (TBT) at Р = 5.5 GPa T = 1900 °C for 4 h on the concentration of single substitutional atoms (P1 centers) in nitrogen-doped synthetic single crystal Ib type diamonds grown by the temperature gradient high-pressure high-temperature (TG-HPHT) method and on their magnetic properties in the temperature range of 2–300 K was investigated. The initial concentration of P1 centers in 2 crystals was 3.0 × 1019 cm−3 and 5.6 × 1019 cm−3, respectively, which decreased by ~96–98 % after TBT. At T < 10 K, an anomalous hysteresis of the magnetic moment is observed in the range of magnetic fields up to Hc = 70 kOe, the amplitude of which is half the value of the paramagnetic saturation moment, corresponding to the number of spins of the P1 centers. The shape of the hysteresis loops after subtracting an intrinsic diamond diamagnetic component and the calculated paramagnetic component indicates a granular (local) superconducting state. The fact that the amplitude of the magnetic moment generated by superconducting currents is equal to half the total number of Bohr magnetons of P1 centers may indicate that elementary currents occur in pairs of adjacent P1 centers. As a result of a decrease in the number of P1 centers in diamonds after TBT, the saturation values of the paramagnetic moment and the amplitude of the diamagnetic moment of the induced superconducting currents decrease proportionally.

Structural, magnetic, and microwave features of Sc3+ ions substituted Sr0.5Ba0.5Fe12O19 nanohexaferrites

In this study, magnetic, structural, and hyperfine interactions of Sc3+ ion substituted Sr0.5Ba0.5Fe12O19 (Sr0.5Ba0.5ScxFe12−xO19 (x ≤ 0.1)) nanohexaferrites (Sc→SrBa NHFs) have synthesized through the sonochemical approach. The structure and morphology were studied by XRD, SEM, HR-TEM, and TEM along with EDX. XRD analysis confirmed the hexaferrite formation having crystallite within the range of 45 to 79 nm. Both TEM, HR-TEM, and SEM analyses proved the hexagonal morphology of all products. All products show ferrimagnetic hysteresis loops at both Ts. The evaluation of M(H) hysteresis loops indicated that the Ms (saturation magnetization), Mr (remanence), Hc (coercivity), and nB(Bohr magneton number) gradually decline with the incorporation of Sc3+ ion. Higher doping contents (x ≥ 0.08) revealed a considerable decline in Mr and Hc, showing significant changes from hard to soft magnetic behavior at higher contents. Mössbauer spectra show that Sc3+ ions are located at commonly octahedral (Oh) 4 f2 site. It was also determined that a small amount of Sc3+ occupied the 2b site. The microwave features of the products were determined by measuring S-parameters within the 2–10 GHz range. It was presumed that the energy losses resulting from reflection encompass both electrical and magnetic loss components. The average value of the reflection coefficient is − 14.48–14.24 dB. A noteworthy attenuation of the reflected wave energy opens up broad prospects for practical applications as coatings for providing electromagnetic compatibility.

Influence of Tm and Tb co-substitution on structural and magnetic features of CoFe[formula omitted]O[formula omitted] nanospinel ferrites

Tm-Tb co-substituted CoFe 2O4 nanospinel ferrites (CoTm xTbxFe2−2xO4, CoTmTb (x = 0.00– 0.03) NSFs)) were prepared via a sonochemical chemical route. The microstructures and morphologies of the NSFs were investigated via XRD, SAED and TEM/SEM, along with EDX techniques. The XRD analysis confirmed the cubic structure all the products along with the absence of any impurities. All the crystallite sizes were observed to be within the range of 9–11 nm. Electron microscopy techniques (SEM, TEM and HR-TEM) proved a cubic morphology in each case and their chemical compositions were confirmed by EDX. The magnetic properties of the synthesized NSFs were investigated via VSM through analysis of the magnetization versus applied magnetic field data. The M–H studies were made at 10 and 300 K. All the NSFs displayed soft ferrimagnetic behavior. It was observed that Tb3+ and Tm3+ ions substitutions provoke substantial variations in the magnetic behavior of the host CoFe 2O4 system. Upon doping the CoFe 2O4 system with the Tb3+ and Tm3+ ions, the magnetic features, Ms (saturation) and Mr (remanent) as well as the Hc (coercive field), increased for x=0.010 and then started to decrease gradually with a further increase in the dopant contents (Tb3+ and Tm3+ ions). The exchange interactions between the cations distributed over the A and B sites is one of the main reasons for the observed evolution in the magnetization magnitudes with the composition. Other factors, like strain, surface spins disorder, crystallite size, size of magnetic domains and Bohr magneton number, were also reported in order to explain the variations in diverse magnetic parameters.

Optical, Charge Transport, Thermal, Magnetic, Plasmonic, and Quantum Mechanical Properties of Iridium

Spectrophotometry has been widely used to retrieve the dielectric function of a bulk iridium sample using an extended version of the Drude–Lorentz model. The parameters of the model are optimized using a spectral-projected-gradient-method-assisted acceptance-probability-controlled simulated annealing approach. Furthermore, optimized values of Drude parameters corresponding to the optical response of electrons and holes (scattering frequency of electrons, the ratio between scattering frequencies of holes and electrons, the ratio between effective masses of electrons and holes, the ratio between the number densities of holes and electrons, and electron volume plasma frequency) are used to evaluate charge transport and magnetic properties. These include static and dynamic conductivities, intrinsic mean free paths, the effective mass of charge carriers and their number densities, Fermi velocities and energies, densities of states at Fermi energies, mobilities, specific heats, Hall’s coefficient, thermal conductivities, charge carrier coupling constant, paramagnetic and diamagnetic susceptibilities, and the number of Bohr magnetons. In addition, optimized resonance energy values of the Lorentz contribution to the dielectric function were compared with the background information provided by density-functional-theory calculations for iridium. A decomposition of the energy loss function was used as the starting point to calculate the effective numbers of bound electrons involved in interband transitions, as well as the densities of states at the final energies of the sets of transitions considered. The Drude–Lorentz model involves charge carrier parameters for both electrons and holes, as well as the resonance energies correlating with the energies associated with quantum transitions. To a large extent, several physical quantities calculated from optimized parameters exhibit values close to those obtained from measurements or by applying other models, including quantum mechanics formulations.

Bi3+ and V3+ co-substituted Ni-Co spinel ferrites: Synthesis, optical, magnetic characterization and hyperfine interaction

Ni0.5Co0.5VxBixFe2-2xO4 spinel ferrite nanoparticles with composition (x = 0.00, 0.02, 0.04, 0.06 and 0.08) (CoNiVBiFeO (x = 0.00–0.08) SFNPs) were well fabricated hydrothermally. The consequence of co-substitution of both Bi3+ and V3+ ions on structure, morphology, and magnetic features of Ni0.5Co0.5Fe2O4 SFNPs were studied using XRD (X-ray diffractometry), scanning (SEM) and transmission (TEM) electron microscopies along with EDX, XPS (X-ray photoelectron spectroscopy), VSM (vibrating sample magnetometry) and Mossbauer spectroscopic techniques. The pure spinel ferrite (SFs) phase was approved via XRD. The morphology of SFNPs were revealed by SEM and TEM. Hyperfine parameters are determined from fitting room temperature Mössbauer spectra. The V3+ and Bi3+ ions occupy mainly at B site. The isomer shift values are coupled with the characteristics of the high spin Fe3+ ion. The influence of V3+ and Bi3+ ions co-doping on the magnetic features of Ni-Co SFNPs has been also investigated at 300 and 10 K. The saturation magnetization (Ms), remanence (Mr), coercive field (Hc), and Bohr magneton number (nB) are extracted from the recorded M-H hysteresis loops. Nanomagnetic materials with x content of 0.02, 0.08, and 0.10 exhibited superparamagnetic (SPM) behavior, whereas other products with x content of 0.00, 0.04, and 0.06 displayed soft ferrimagnetic behavior at ambient temperature. The different prepared nanoferrites displayed hard ferrimagnetic characteristic at 10 K. The Ms and Mr values are decreased as result of V3+ and Bi3+ ions co-doping. However, Hc does not show a monotonic trend. The fluctuations in magnetic moments of ions, super-exchange coupling, and distribution of cations are correlated with the changes in magnetic parameters to explain their variations.

Synthesis of a mixed‐valent europium(II, III)‐borate and its optical and magnetic behavior

AbstractThe mixed‐valent, europium borate Eu5(BO3)4 was synthesized from Eu2B2O5 and EuB2O4. Its structure was refined by Rietveld analysis. Eu5(BO3)4 crystallizes in space group Pnma (a=2229.77(2) pm, b=1599.91(2) pm, and c=877.75(1) pm) and was found to be isostructural with Eu5(BO2.51N0.49)4. Powder reflectance spectra (UV/vis/NIR) and magnetic susceptibility data of Eu5(BO3)4 and of the reference compounds EuIIB4O7 and EuIIIBO3 were measured. The spectrum of the mixed‐valent europium(II, III) borate shows the 7F0→7F6 transition of the Eu3+ ion and the intervalence charge transfer Eu2+→Eu3+. The experimental Bohr magneton number of Eu5(BO3)4, μobs/μB=14.90, agrees well to μcalc/μB for a combination of three Eu2+ and two Eu3+ per formula.

Magnesium and yttrium doped superparamagnetic manganese ferrite nanoparticles for magnetic and microwave applications

Magnesium and yttrium doped manganese ferrite nanoparticles based on chemical formula MgxMn1-xYxFe2-xO4 (x = 0.0, 0.05, 0.10, 0.15) have been prepared by chemical coprecipitation technique and calcined to 600 °C. Thereafter, structural, morphological, optical, magnetic and dielectric investigations were performed. X-ray diffraction (XRD) suggests that the grown composition is cubic spinel. Parameters like crystallite size, lattice parameter, unit cell volume and theoretical density were determined. The crystallite size has been found to decrease from 47 nm to 37 nm for x = 0.0–0.15 respectively. Scanning electron microscope (SEM) equipped with energy dispersive X-ray (EDAX) has been used to investigate the morphology and elemental analysis. The optical band gap calculated using Kubelk-Munk (K-M) method increases from 1.84 eV for x = 0 to 2.35 eV for x = 0.15. The spin characteristics investigated through electron paramagnetic resonance (EPR) spectroscopy gives various parameters like g-value, resonance field (Hr), peak to peak line width (Hpp) and relaxation time (τ2). The value of g is determined and comes out to be 2.086, 2.047, 2.043 and 2.039 for x = 0.0, 0.05, 0.10 and 0.15 respectively. The hysteresis curves obtained using vibrating sample magnetometer (VSM) shows ferrimagnetic behavior of composition. Saturation magnetization (Ms), retentivity (Mr), coercivity (Hc), remenance ratio (Mr/Ms), anisotropy constant (K1) and Bohr magneton number (n) were determined. The value of saturation magnetization decreases from 18.12 emu/g to 7.4 emu/g when the doping concentration increases from x = 0.0 to 0.15. Mr and Hc values are small representing the superparamagnetism. Mr/Ms suggests the single domain structure. The dielectric constant shows frequency dispersion which is typical in spinel ferrites. The value of dielectric constant is high in pure manganese ferrite and decreases with increase in Mg2+ and Y3+ content e.g., at 2.5 kHz the value of dielectric constant is 62 for x = 0.0 and 22 for x = 0.15.

Physical properties of rhodium retrieved from modeling its dielectric function by a simulated annealing approach

Optical, charge carriers transport, quantum mechanics, magnetic, thermal, and plasmonic properties of the transition metal rhodium are considered. An extended Drude-Lorentz (DL) model is applied to describe the dielectric function (DF) of rhodium in a spectral range going from the mid-infrared (12.4 μm) to the vacuum ultraviolet (32 nm). The Drude term of the DF includes, as optimization parameters, the inverse of the high frequency dielectric constant, the volume plasma frequency and scattering frequency of the electrons, the scattering frequency of holes relative to that of electrons, the ratio between the effective masses of electrons and holes, the number of holes per atom relative to that of electrons, and the renormalized times between grain boundary scattering events for electrons and holes. The Lorentz contribution to the DF includes the number of conduction electrons per atom, the oscillator strengths, the resonance energies, and the Lorentzian widths. Values of the parameters involved in the DF are optimized by an acceptance-probability-controlled simulated annealing method that minimizes spectral differences between the real and imaginary parts of the DF values obtained from the literature and those evaluated from the DL parametric formulation, accounting for the presence of electrons and holes as charge carriers. Once an optimized spectral description of the DF of rhodium is obtained, a large set of charge-transport, magnetic, thermal, plasmonic, and quantum mechanics derived quantities are evaluated: mobilities, relaxation times, Fermi velocities, effective masses, electrical and thermal conductivities, heat capacity coefficients, Hall coefficient, diamagnetic and paramagnetic susceptibilities, effective number of Bohr magnetons, Fermi energies and corresponding densities of states, energy loss functions, effective number of charge carriers participating in conduction, and effective number of electrons involved in inter-band transitions.

Understanding Optical Absorption Spectra and Magnetic Behavior of a Wide Range of Samarium(III) Oxo‐Compounds: Analysis of the Ligand‐Field Effects

AbstractIn this study powder reflectance spectra as well as temperature dependent magnetic susceptibilities of eight different samarium(III) oxo‐compounds (SmP5O14, SmPO4, SmVO4, SmNbO4, SmTaO4, Sm2Ti2O7, SmAsO4, B‐type Sm2O3 and C‐type Sm2O3) have been measured. In addition, high‐resolution electronic absorption spectra in the near infrared of single crystals of seven of these compounds are reported. Comparing our experimental data to the results of ligand field analyses (angular overlap model AOM allowing for decomposition of the global ligand field into the contributions of the individual ligands; computer program BonnMag) shows reasonable agreement of electronic transition energies in optical spectra and a good fit of the temperature dependent Bohr magneton numbers μeff/μB. Analysis of the ‘best fit’ AOM parameters reveals a significant variation in the nephelauxetic effect with F2=379 cm−1 for SmP5O14 and F2=356 cm−1 for KSmO2. A trend in the variation of the AOM parameter eσ with the optical basicity Λ is discussed. The values for eσ(Sm−O), normalized to d(Sm−O)=2.38 Å, range from 337 cm−1 for SmP5O14 to 573 cm−1 for KSmO2. For the ratio eπ/eσ only a negligible influence on the match between calculated and experimental data is observed. For the relation of eσ(Sm−O) to the interatomic distance d(Sm−O) the correlation eσ(Sm−O) ∼1/d7(Sm−O) was found to reproduce in AOM the observed ligand field splitting well. For SmPO4 a high resolution, low temperature (110 K) spectrum allows the assignment of hot bands.

Y3+ composition and particle size influenced magnetic and dielectric properties of nanocrystalline Ni0.5Cu0.5YxFe2-xO4 ferrites

The rare earth Yttrium (Y3+) doped Ni–Cu nanoferrites (NCY ferrites) with chemical formulation, Ni0.5Cu0.5YxFe2-xO4 (x = 0–0.125) were prepared successfully by the sol gel route. The X-ray diffraction (XRD) of NCY ferrites revealed that a single phase of cubic spinel is created within the synthesized ferrites. The crystallite sizes obtained by XRD pattern are in the range of 51–84 nm, in good agreement with those obtained by transmission electron microscopy (TEM) and field emission scanning electron microscopy (FSEM). The calculated lattice parameter of NCY ferrite unit cells initially decreases up to x = 0.1 and increase afterwards for x = 0.125. From FESEM and TEM micrographs, surface morphology and microstructure of NCY nanoferrites were studied. The energy dispersive X-ray spectroscopy (EDS) patterns have confirmed the stoichiometric presence of Ni, Cu, Y, O and Fe, those were used to prepare the samples. The variations in the magnetic properties with Y3+ compositions were investigated by obtaining the hysteresis loops of NCY ferrites. The magnetic hopping lengths LA and LB were calculated from XRD. The saturation magnetization, Bohr magneton number, coercivity and retentivity of the ferrites were influenced by the structural parameters like crystallite size and lattice strain. The frequency variation of dielectric constant and loss tangent exhibit space charge polarization as a phenomenon governing the dielectric behavior of the ferrites.

Preparation, structure and magnetic, electronic and thermal properties of Dy3+-doped ZnCr2Se4 with unique geometric type spin-glass

Physico-chemical studies of (Zn1–xDyx)Cr2Se4 and Zn[Cr2–xDyx]Se4 spinel systems (x ​= ​0.05, 0.10) containing dysprosium ions in both tetra- and octahedral positions have shown an enhancement of long-range antiferromagnetic interactions and a weakening of short-range ferromagnetic ones. This resulted in the appearance of geometric type spin-glass in connection with the increase in the length of chemical bonds between chromium ions. This state of spin-glass is also due to the large difference in the absolute values of the superexchange integrals and the small magnetic contribution to the specific heat below the freezing point. Studies of XPS and X-ray absorption near edge structure (XANES) showed that no main edge shift was observed between the tetra- and octahedral positions of dysprosium ions, which indicates that they remain in the +III oxidation state. Thus, significant differences between the effective magnetic moment and the effective number of Bohr magnetons, as well as much higher saturation magnetization values above 6 μB, suggest that chromium ions may have a different oxidation state. These effects may be also generated by spin defects.

Cationic distribution in nanoparticles of ferrites of ZnxFe3-xO4 composition

Nanodispersed powders of zinc-substituted magnetite ZnxFe3-xO4 with the content of zinc ions x = 0.0 ÷ 0.5 were synthesized by the method of chemical condensation. X-ray spectra showed single-phase powders and their belonging to the cubic structure of spinel-type ferrite. According to the results of X-ray and electron microscopic studies, the particle sizes for all synthesized systems were determined. The average particle size of ferrites according to data obtained from X-ray spectra using the Selyakov-Shearer formula was ~ 7 nm, with a maximum particle size of about 10 nm. According to microscopy, the particle size range was 3 ÷ 13 nm with an average value of 6.5 nm. The study of cation distribution was carried out in two ways. The Poix method was chosen as the first method, which is based on the relationship between the lattice parameter a and the characteristic cation-anion distances. The second method was chosen to determine the cation distribution by measuring the magnetization. The formula for coupling the specific magnetization at 0 K with the number of Bohr magnetons per formula unit was used. An amendment was introduced into the formula due to the small particle size and, accordingly, the large share contribution of the near-surface region with a "canted" magnetic structure. The parameters of the crystal lattice and the magnetization were measured. The obtained data formed the basis of cation distribution calculations, according to which ferrites with a concentration of x ≤ 0.2 have an inverted spinel structure, ie zinc ions are localized only in octahedral positions, and at a concentration of 0.3 ≤ x ≤ 0.5 – a mixed spinel structure with a minimum degree of inversion of 80% at a concentration of zinc ions x = 0.5.

The crystallographic, magnetic, and electrical properties of Gd3+-substituted Ni–Cu–Zn mixed ferrites

Polycrystalline Ni0.48Cu0.12Zn0.40GdxFe2-xO4 (where x = 0.00, 0.02, 0.04, 0.08, and 0.10) was synthesized by the conventional solid-state reaction technique. The structure and surface morphology were studied by X-ray diffraction (XRD) and high-resolution optical microscopy, respectively. The XRD patterns indicated that the compositions formed a cubic spinel structure for a small amount of Gd3+ substitution. With increasing Gd3+ concentration, a gradual rise in the intensity of the extra peaks was observed, and those peaks were identified as corresponding to GdFeO3 (orthoferrite). Rietveld refinement was performed on the XRD data of Gd3+-substituted Ni0.48Cu0.12Zn0.40 ferrite samples for further verification, and the results were found to be in good agreement with results reported in the literature. Variation of the lattice constant obeyed Vegard's law. Microstructural studies showed that the average grain diameter increases as the Gd3+ content increases up to an optimum concentration and then it decreases. Magnetic properties were characterized by the complex initial permeability (100 Hz–100 MHz). The real part of the complex initial permeability (μi′) increases with Gd3+ concentration up to x = 0.04 and then decreases. Ni0.48Cu0.12Zn0.40Gd0.04Fe1.96O4 shows the highest value of μi′ (at the optimum sintering temperature), which is more than eight times that of the parent sample. Conversely, magnetic loss is reduced remarkably in this composition. The Néel temperature was determined from the temperature-dependent initial complex permeability, which showed a decreasing trend with increase in Gd3+ concentration owing to the weakening of the A-B interaction. DC magnetizations as a function of the applied magnetic field were evaluated with a vibrating-sample magnetometer at room temperature. The magnetization increased with increasing Gd3+ content up to x = 0.04 owing to the variation of cation distribution and then reduced because of the possibility of noncollinear spin arrangement with further increase of Gd3+ content. The number of Bohr magnetons (nB) and the Yaffet-Kittel angle (αY-K) were evaluated. The calculated αY-K values were a minimum for x = 0.04, while the nB variation showed the opposite trend. Because of the reduction of electron exchanges between Fe2+ and Fe3+ at the octahedral site, the room temperature dielectric constant and the dielectric loss were reduced with increasing Gd3+ content. There was an exceptional increase in the dielectric constant for x = 0.02 sample. The AC conductivity spectrum exhibited two regions, and the conductivity was found to decrease with the addition of Gd3+. Impedance spectroscopy studies indicated a non-Debye-type relaxation process. Ferroelectric transition temperatures, TC, were also determined from measurement of the temperature-dependent dielectric constant.

Site occupancy, valence state, and spin state of Co ions in Co-doped In2O3 diluted magnetic semiconductor

Abstract This study aims to investigate the 24 d and 8 b site occupancies, valence state, and spin state of Co ions in Co-doped In2O3 prepared by a chemical solution method. The Rietveld analysis of X-ray powder diffraction patterns of the products revealed that Co2+ and Co3+ ions tend to occupy the 24 d and 8 b sites, respectively. X-ray photoelectron spectroscopy analysis indicated that the Co2+ ions are dominant at low-doping region ( x ≤ 0.044 ) and that Co3+ ions appear at high-doping region ( x ≥ 0.052 ). Magnetic susceptibility measurements revealed that the effective Bohr magneton number p e f f is ~3.8 at the low-doping region, consistent with the value for Co2+ in the high-spin ( S = 3 / 2 ) state. The p e f f decreases at the high-doping region, where Co3+ ions appear. These results indicate that the Co3+ ions are in the low-spin ( S = 0 ) state or intermediate-spin ( S = 1 ) state.

Effect of Nb3+ ion substitution on the magnetic properties of SrFe12O19 hexaferrites

The crystal structure and magnetic properties of SrNbxFe12–xO19 (0.00 ≤ x ≤ 0.08) nanohexaferrites (NHFs) fabricated using a sol–gel technique is presented in this study. The X-ray powder diffractometry (XRD) and Infrared spectroscopy (FT-IR) confirmed the formation of M-type hexaferrite phase. The analyses of magnetization versus applied magnetic field, M(H), were performed at room (300 K; RT) and low (10 K) temperatures. The Bohr magneton number (nB), saturation (Ms) and remanent (Mr) magnetization values increase slightly with increasing Nb3+ content. The room-temperature values of the magnetic parameters Mr = 31.41–33.28 emu/g, Ms = 57.10–60.14 emu/g and coercivity (Hc) between 4274 and 4540 Oe, at 10 K, magnetization data were detected that are much higher with respect to RT values: Mr = 45.96–51.06 emu/g, Ms = 94.42–95.99 emu/g. The magnetic results indicate that the samples are magnetically hard materials at both considered temperatures. The squareness ratio (SQR) is found to be around 0.50, implying single-domain NPs with uniaxial anisotropy for pristine and substituted samples. With exception, the x = 0.0 sample indicated the formation of multi-domain structure with uniaxial anisotropy at 10 K. Field cooling (FC) susceptibility measurements were applied in temperature range of 5–350 K for pristine sample and samples that contained some Nb3+ ions. The analyses of dc susceptibility data also proved that Nb3+ ion substitution increases the magnetization and, additionally, allows for an easier alignment of the magnetic domains. The obtained magnetic results were investigated deeply with relation to structural and microstructural properties. The observed remanent magnetization (Mr) and coercivity (Hc) render the products are useful for permanent magnets and high-density recording media.

Mechanisms for enhanced catalytic performance for NO oxidation over La2CoMnO6 double perovskite by A-site or B-site doping: Effects of the B-site ionic magnetic moments

Diesel engine exhaust has been identified to be highly carcinogenic. In order to improve the control of diesel engine exhaust emissions, the diesel engine oxidation catalyst (DOC) + catalytic diesel particulate filter (CDPF) + selective catalytic reduction catalyst (SCR) + NH3 oxidation catalyst (ASC) united technology has become the mainstream technology for catalytic aftertreatment. Perovskite oxides have emerged as a promising catalyst for NO oxidation and can be used as the DOC. Undoped La2MMnO6 (M = Co, Fe, Ni, Cu) double perovskites, A-site Ba-doping (La2-xBax)CoMnO6 (%Ba = 0, 25%, 50%, 75%, 100%) perovskites and B-site Cu-doping La2Co1-yCuyMnO6 (y = 0, 0.25, 0.50, 0.75, 1) double perovskites were prepared by a facile molten-salt synthesis method and examined by XRD, SEM, BET, in situ DRIFTS, and XPS. In addition, we calculated the B-site ionic magnetic moments of the double perovskites μ which were contributed by the effective Bohr magneton number np of the B-site 3d transition metal ions, such as Mn3+, Mn4+, Co3+, Fe3+, Ni2+, and Cu2+. The correlations between the B-site ionic magnetic moments and the maximum NO conversion over all those double perovskites were also calculated. The B-site ionic magnetic moments has a strong positive correlation with the highest conversion rate of NO catalytic oxidation over all those double perovskites. That is, the higher the B-site ionic magnetic moments, the better the catalytic oxidation performance of NO over the double perovskites. So enhancing the B-site ionic magnetic moments by A-site doping is a method to improve the catalytic activity of NO oxidation over the perovskites. Increasing the B-site ionic magnetic moments is the key index to improve the catalytic activity of NO oxidation of the double perovskites by B-site doping.

Optical Spectra and Magnetic Behavior of a Wide Range of Europium(III) Oxo-Compounds: Analysis of the Ligand-Field Effects.

The europium-oxygen interaction in nine different europium(III) oxo-compounds (including C-type Eu2O3) was investigated on the basis of powder reflectance spectra (near-IR/vis/UV) and temperature-dependent magnetic measurements. Computation of the transition energies and of the effective Bohr magneton numbers for Eu3+ in the different ligand fields were performed within the framework of the angular overlap model (AOM) using the computer program BonnMag. These calculations show that all electronic transition energies in the optical spectra, the magnetic susceptibilities as well as their temperature dependence, are very well-accounted for by AOM. BonnMag provides a facile way to perform these calculations. Analysis of the obtained "best fit" AOM parameters eσ(EuIII-O) shows that these are significantly influenced by the further bonding partners of oxygen ("second-sphere ligand-field effect"). An increase of eσ,max(EuIII-O) from 404 cm-1 (EuPO4) to 687 cm-1 (EuSbO4), both normalized to d(EuIII-O) = 2.38 Å, is found. Correlation of this variation to oxide polarizability and optical basicity of the oxo-compounds is discussed.

Surfactant-assisted production of TbCu2 nanoparticles

The production of surfactant-assisted metallic nanoparticles of TbCu2 has been achieved by the combination of high-energy ball milling in tungsten carbide containers and the use of oleic acid (C18H34O2) and heptane (C7H16). The alloys were first produced in bulk pellets by arc melting and subsequently milled for only 2 and 5 h in oleic acid (15 and 30% mass weight). The powders consist of an ensemble of nanoparticles with a TbCu2 lattice cell volume of ≈215 Å3, an average particle diameter between 9 and 12 nm and inhomogeneous lattice strain of 0.2–0.4%, as deduced from X-ray diffraction data. The nanometric sizes of the crystals with defined lattice planes are close to those obtained by transmission electron microscopy. Raman spectroscopy shows the existence of inelastic peaks between 1000 and 1650 cm−1, a characteristic of C18H34O2. The magnetisation shows a peak at the antiferromagnetic-paramagnetic transition with Néel temperatures around 48 K (below that of bulk alloy) and a distinctive metamagnetic transition at 5 K up to 40 K. The Curie-Weiss behaviour above the transition reveals effective Bohr magneton numbers (≈9.1–9.9 μB) which are close to what is expected for the free Tb3+ ion using Hund’s rules. The metamagnetic transition is slightly augmented with respect to the bulk value, reaching H = 24.5 kOe by the combined effect of the size reduction and the lattice strain increase and the increase of magnetic disorder. At low temperatures, there is irreversibility as a result of the existing magnetic disorder. The moment relaxation follows an Arrhenius model with uncompensated Tb moments, with activation energies between 295 and 326 K and pre-exponential factors between 10−11 and 10−13 s. The results are interpreted as a consequence of the existence of a diamagnetic surfactant which drastically decreases the magnetic coupling between interparticle moments.