Nanostructured Fe50Ni50 alloy formed by chemical reduction

A high purity Fe₅₀Ni₅₀ nanometric alloy was synthesized by ultra rapid autocatalytic chemical reduction of the corresponding transition metal ions in an aqueous solution. The ratio of metal concentration in solution is preserved in the precipitated powder alloy and no metal segregation has been detected. The alloy was characterized as a nanostructured chemically disordered taenite phase by X-ray diffraction (XRD) and Mössbauer spectroscopy (MS). Transmission electron microscopy (TEM) showed that the as prepared alloy contained spherical particles with 96 nm mean diameter size. The particles are composed of crystallites (of ∼15 nm size) and a predominant disordered interfacial region. A thermal treatment of 673 K/2 h produced a structural relaxation with a significant narrowing in the XRD and Mössbauer lines with a exothermic flow in the DSC signal and an increase in the crystallite size to 30 nm.     

Study of magnetic phases in mechanically alloyed Fe50Zn50 powder

The mechanosynthesis of Fe₅₀Zn₅₀ alloy resulted in the formation of the bcc Fe(Zn) solid solution after 20 h of milling. Structural transformations induced by mechanical alloying and heating, and magnetic properties of the powders were studied by Mössbauer spectroscopy, X-ray diffraction, Faraday balance and vibrating sample magnetometry techniques. All alloys studied exhibit strong magnetic ordering with Curie temperatures close to 900 K. Room temperature Mössbauer measurements revealed distinguished magnetic environments in the samples. The decrease of coercivity with prolonged milling time was attributed to the reduction or averaging of local magnetic anisotropies.     

Hyperfine interactions in some Aurivillius Bim+1Ti3Fem−3O3m+3 compounds

X-ray diffraction and Mössbauer spectroscopy were applied as complementary methods to investigate the structure and hyperfine interactions in the series of Bi_m+1Ti₃Fe_m−3O_3m+3 Aurivillius compounds with m=4, 6, 7 and 8. Samples were synthesized by the solid-state sintering method at various temperatures. As X-ray diffraction analysis proved, the compounds formed single phases at temperature above 993 K. Mössbauer studies have confirmed diffraction measurements. Compounds synthesized at 993 K contained residual hematite, however these sintered at elevated temperatures were single-phased materials. Room-temperature Mössbauer spectra of Bi_m+1Ti₃Fe_m−3O_3m+3 compounds revealed their paramagnetic properties, what is consistent with the literature data concerning the Néel temperature of these ceramics (T_N is smaller than room temperature). Detailed analysis of MS spectra allowed to state that iron ions may occupy both tetrahedral and octahedral sites in the crystallographic lattice of Aurivillius compounds.     

X-ray diffraction,microstructure, Mössbauer and magnetization studies of nanostructured Fe50Ni50 alloy prepared by mechanical alloying

Nanocrystalline Fe₅₀Ni₅₀ alloy samples were prepared by the mechanical alloying process using planetary high-energy ball mill. The alloy formation and different physical properties were investigated as a function of milling time, t, (in the 0–50 h range) by means of the X-ray diffraction (XRD) technique, scanning electron microscopy (SEM), energy dispersive X-ray (EDAX), Mössbauer spectroscopy and the vibrating sample magnetometer (VSM). The complete formation of γ-FeNi is observed after 24 h milling. When milling time increases from 0 to 50 h, the lattice parameter increases towards the Fe₅₀Ni₅₀ bulk value, the grain size decreases from 67 to 13 nm, while the strain increases from 0.09% to 0.41%. Grain morphologies at different formation stages were observed by SEM. Saturation magnetization and coercive fields derived from the hysteresis curves are discussed as a function of milling time.     

Evolution of structure, microstructure and hyperfine properties of nanocrystalline Fe50Co50 powders prepared by mechanical alloying

Nanostructured Fe₅₀Co₅₀ powders were prepared by mechanical alloying of Fe and Co elements in a vario-planetary high-energy ball mill. The structural properties, morphology changes and local iron environment variations were investigated as a function of milling time (in the 0-200 h range) by means of X-ray diffraction, scanning electron microscopy (SEM), energy dispersive X-ray analysis and ⁵⁷Fe Mössbauer spectroscopy. The complete formation of bcc Fe₅₀Co₅₀ solid solution is observed after 100 h milling. As the milling time increases from 0 to 200 h, the lattice parameter decreases from 0.28655 nm for pure Fe to 0.28523 nm, the grain size decreases from 150 to 14 nm, while the meal level of strain increases from 0.0069% to 1.36%. The powder particle morphology at different stages of formation was observed by SEM. The parameters derived from the Mössbauer spectra confirm the beginning of the formation of Fe₅₀Co₅₀ phase at 43 h of milling. After 200 h of milling the average hyperfine magnetic field of 35 T suggests that a disordered bcc Fe-Co solid solution is formed.     

Synthesis and characterization of the xZnO-(1−x)α-Fe2O3 nanoparticles system

The xZnO-(1−x)α-Fe₂O₃ nanoparticles system has been obtained by mechanochemical activation for x=0.1, 0.3 and 0.5 and for ball milling times ranging from 2 to 24 h. Structural and morphological characteristics of the zinc-doped hematite system were investigated by X-ray diffraction (XRD) and Mössbauer spectroscopy. The Rietveld structure of the XRD spectra yielded the dependence of the particle size and lattice constant on the amount x of Zn substitutions and as function of the ball milling time. The x=0.1 XRD spectra are consistent with line broadening as Zn substitutes Fe in the hematite structure and the appearance of the zinc ferrite phase at milling times longer than 4 h. Similar results were obtained for x=0.3, while for x=0.5 the zinc ferrite phase occurred at 2 h and entirely dominated the spectrum at 24 h milling time. The Mössbauer spectra corresponding to x=0.1 exhibit line broadening as the ball milling time increases, in agreement with the model of local atomic environment. Because of this reason, the Mössbauer spectrum for 12 h of milling had to be fitted with two sextets. For x=0.3 and 12 milling hours, the Mössbauer spectrum reveals the occurrence of a quadrupole-split doublet, with the hyperfine parameters characteristic to zinc ferrite, ZnFe₂O₄. This doublet clearly dominates the Mössbauer spectrum for x=0.5 and 24 h of milling, demonstrating that the entire system of nanoparticles consists finally of zinc ferrite. As ZnO is not soluble in hematite in the bulk form, the present study clearly demonstrates that the solubility limits of an immiscible system can be extended beyond the limits in the solid state by mechanochemical activation. Moreover, this synthesis route allowed us to reach nanometric particle dimensions, which would make the materials very important for gas sensing applications.     

Sol–gel synthesis of 8 nm magnetite (Fe3O4) nanoparticles and their magnetic properties

Magnetite (Fe₃O₄) nanoparticles were successfully synthesized by a sol–gel method. The obtained nanoparticles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive analysis by X-ray (EDAX), transmission electron microscopy (TEM), superconducting quantum interference device (SQUID) and Mössbauer spectrometry. XRD and Mössbauer measurements indicate that the obtained nanoparticles are single phase. TEM analysis shows the presence of spherical nanoparticles with homogeneous size distribution of about 8 nm. Room temperature ferromagnetics behavior was confirmed by SQUID measurements. The mechanism of nanoparticles formation and the comparison with recent results are discussed. Finally, the synthesized nanoparticles present a potential candidate for hyperthermia application given their saturation magnetization.     

Enzymes immobilization on Fe3O4-gold nanoparticles

In the present study Fe₃O₄ magnetic nanoparticles were synthesized by coprecipitation of Fe²⁺ and Fe³⁺ from chlorides. In the next step magnetite-gold core-shell nanoparticles were synthesized from HAuCl₄ using an ethanol as a reducing agent. Finally, magnetic nanoparticles were functionalized by hexadecanethiol. The immobilization of biological molecules (trypsin and glucose oxidase) to the thiol-modified and unmodified magnetite-gold nanoparticles surface was tested. The resulting nanoparticles were characterized by infrared spectroscopy, differential scanning calorimetry, Mössbauer spectroscopy and transmission electron microscopy.     

Effects of annealing temperature on structure and magnetic properties of amorphous Fe61Co27P12 nanowire arrays

Arrays of Fe₆₁Co₂₇P₁₂ nanowire with an aspect ratio about 70 were prepared in anodic aluminum oxide templates by electrodeposition. The influences of annealing temperature on structure and magnetic properties of Fe₆₁Co₂₇P₁₂ nanowires were studied. When the specimens were annealed below 400 °C, there are no obvious changes in structure except relaxation. With the annealing temperature increasing from 400 to 600 °C, the Fe-Co phase is detected by X-ray diffraction and Mössbauer spectra. The crystalline fraction and hyperfine field can be derived from Mössbauer spectra. The room temperature magnetic hysteresis loops show that the coercivity and squareness of the nanowire arrays in parallel to the wire axis increase with the increasing of annealing temperature, which mainly attributes to the strengthening of anisotropy.     

Structure and superconductivity in FexCu1−xBa2YCu2O7+y superconductors synthesized by high pressure

Comprehensive studies of X-ray diffraction, oxygen content, superconductivity and Mössbauer effect have been made on Fe_xCu_1−xBa₂YCu₂O_7+y superconductors (0.00≤x≤0.70) synthesized by ambient (AM) and high pressure (HP). Results indicate that all the HP-samples have tetragonal structure, smaller lattice parameter c and unit-cell volume than the AM-samples. The studies of oxygen content, and Mössbauer spectroscopy indicate that the HP-samples have higher oxygen content, carrier concentration and average valence of Fe than the AM-samples. Moreover, for the HP-samples more Fe atoms located in CuO_x chains have fivefold-oxygen coordination. These are important reasons for the enhancement of T_c in the HP-samples.     

Structural study by X-ray diffraction and Mössbauer spectroscopy of a new synthetic iron phosphate: K4MgFe3(PO4)5

A new iron phosphate K₄MgFe₃(PO₄)₅ has been synthesized by the flux method and characterized by single-crystal X-ray diffraction and Mössbauer spectroscopy. It crystallizes in the tetragonal system with the space group and the unit cell parameters a=9.714(3) Å and c=9.494(5) Å. The crystal structure is of a new type. It exhibits a three-dimensional framework built up from corner-sharing MO₅ (M=0.75Fe+0.25Mg) trigonal bipyramids and PO₄ tetrahedra. The K⁺ ions are occupying large eight-sided tunnels running along c. A room temperature Mössbauer study confirmed the +3 valence state of iron and its five-coordination.     

Magnetic properties of nanocrystalline Ni0.7Mn0.3Gd0.1Fe1.9O4 ferrite at low temperatures

Mössbauer spectra and magnetic measurement of Ni_0.7Mn_0.3Gd_0.1Fe_1.9O₄ ferrite were investigated by Oxford MS-500 Mössbauer spectrometer and superconducting quantum interference device (SQUID) magnetometer with a field 5 T. Ni_0.7Mn_0.3Gd_0.1Fe_1.9O₄ nanoparticles have a considerable coercivity of 1040 Oe when the test temperature is reduced to 2 K. Mössbauer spectra show that Ni_0.7Mn_0.3Gd_0.1Fe_1.9O₄ nanoparticles exhibit superparamagnetism at room temperature and ferrimagnetism at 77 K.     

Magnetic properties of RE0.7Ca0.3Mn0.95Fe0.05O3 (RE=Sm and Gd) manganites at low temperature

The magnetic properties of RE_0.7Ca_0.3Mn_0.95Fe_0.05O₃ perovskite with rare-earth cations (RE=Sm and Gd) were investigated by means of X-ray diffraction, Mössbauer spectroscopy, and low temperature (4.2-266 K) magnetization measurements. Structural characterization of these compounds shows that they both have orthorhombic (Pbnm) structure. The Mössbauer spectra show clear evidence of local structural distortion of the Mn(Fe)O₆ octahedron, which is based on the non-zero nuclear quadrupole interactions for high-spin Fe³⁺ ions. It was found that the local structural distortion increases significantly when Sm³⁺ is replaced by Gd³⁺. This distortion is attributed to the Jahn-Teller coupling strength as estimated from the Mössbauer effect results. The magnetic results indicate that the Curie temperature decreases as a result of replacing Sm by Gd. This is due to the decrease of the average A-site cationic radius 〈r_A〉. The rapid increase of magnetization at low temperature indicates the magnetic ordering of rare earth ions at the A-site.     

Structural and magnetic studies on mechanosynthesized BaFe12−xMnxO19

Barium hexaferrite powders with manganese substitution were prepared by mechanosynthesis. The structural and magnetic properties were characterized by X-ray diffractometer and vibration sample magnetometer, respectively. XRD patterns were refined by Rietveld method. Preferential site occupation of manganese ion was investigated by room temperature (RT) Mössbauer measurements. XRD results showed a single-phase barium hexaferrite with some residual hematite. Crystallite size was observed to decrease with substitution amount. Lower saturation magnetization and increased coercivity is observed in substituted samples. RT Mössbauer measurements showed that manganese ions preferentially occupy 12k, 4f₂, and 2a sites.     

Temperature-dependent Mössbauer and dielectric studies of Mg0.95Mn0.05Fe1.0Ti1.0O4

The effect of tetravalent Ti⁺⁴ substitution in Mg_0.95Mn_0.05Fe₂O₄ on its magnetic and electrical properties has been studied using X-ray diffraction, Mössbauer spectroscopy, isothermal dc magnetization and dielectric measurements. X-ray diffraction studies have shown the structural transformation from cubic to tetragonal with the Ti⁺⁴ substitution. The Mössbauer spectra of Mg_0.95Mn_0.05Fe_1.0Ti_1.0O₄ recorded in the temperature range 20-300 K shows the presence of the magnetic as well as quadrupole interactions. The isothermal hysteresis loop infers that the system exhibits a ferrimagnetic ordering at room temperature. The Zero-field-cooled (ZFC) and field-cooled (FC) magnetization studies support ferrimagnetic ordering of Mg_0.95Mn_0.05Fe_1.0Ti_1.0O₄ at room temperature. Signatures of ferroelectric transition have been observed in the temperature range 200-300 K from dielectric measurements. The observed magnetic and dielectric behaviour indicate that this material exhibits multiferroic behaviour.     

Investigating the formation and magnetic properties of the Dy0.75Fe1.25O3 orthoferrite prepared by sol-gel method

In this paper, the Dy_0.75Fe_1.25O₃ orthoferrite nanoparticles were synthesized successfully by sol-gel method. Dy_0.75Fe_1.25O₃ orthoferrite nanoparticles are obtained by calcining the flakes at 600 and 700 °C. The magnetic properties of the different samples are investigated using Quantum Design MPMS SQUID magnetometer and MS-500 Mössbauer spectrometer. Magnetic phase γ-Fe₂O₃ coexists in the samples calcined at 600 °C and orthoferrite phase is completely recovered in the samples calcined at 700 °C. Although excessive Fe³⁺ ions were introduced, none of these iron spins couple magnetically with Dy³⁺ ions.     

Electro-precipitation of Fe3O4 nanoparticles in ethanol

The preparation of superparamagnetic magnetite (Fe₃O₄) nanoparticles by electro-precipitation in ethanol is proposed. Particle average size can be set from 4.4 to 9 nm with a standard deviation around 20%. Combination of wide-angle X-ray scattering (WAXS), Electron energy loss spectroscopy (EELS) and Mössbauer spectroscopy characterizations clearly identifies the particles as magnetite single-crystals (Fe₃O₄).     

In-plane magnetic anisotropies in Ni/FeMn and Ni90Fe10/FeMn exchange biased bilayers

The in-plane magnetic anisotropy in Ni/FeMn and Ni₉₀Fe₁₀/FeMn exchange-biased bilayers prepared by co-evaporation under molecular beam epitaxy conditions is investigated employing longitudinal magneto-optical Kerr effect (MOKE) and ferromagnetic resonance (FMR). The exchange anisotropy was induced by a magnetic field cooling immediately after the deposition of the bilayers. Besides the induced term, the presence of an additional uniaxial anisotropy in the FM layers was detected both by MOKE and FMR, and the characteristic directions of these two anisotropy terms are not coincident. The interplay between the anisotropy contributions is discussed considering micromagnetic simulations and the in-plane resonance condition for different magnetic field orientation. X-ray diffraction, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy were used to complement the characterization of the samples.     

A study of nanosized Ni substituted Co–Zn ferrite prepared by coprecipitation

Nanoparticles of Ni_0.25Co_0.25Zn_0.5Fe₂O₄ with different particle sizes were synthesized by chemical coprecipitation technique. The prepared nanoparticles were characterized and studied by X-ray diffraction, room temperature ⁵⁷Fe Mössbauer spectroscopy and DC magnetization. Increase in annealing temperature leads to inversion of cations from their normal configurations which results in an increase in the hyperfine fields at both tetrahedral A and octahedral B sites. The decrease in saturation magnetization values with an increase in annealing temperature can be attributed to the variation in proportions of superparamagnetic phase and also the redistribution of cations in these ferrite nanoparticles. Variation of coercivity with annealing temperatures can be explained in terms of the size effect.