Magnetic Properties of Nanocrystalline Fe x Cu1−x Alloys Prepared by Ball Milling

Hyperfine Interactions - X-ray diffraction, Mössbauer and magnetization measurements were used to study Fe x Cu1?x alloys prepared by ball-milling. The X-ray data show the formation of a...     

Mössbauer Studies of Fe0.7−x Si0.3Mn x Alloys

Hyperfine Interactions - In this work we present Fe57 Mössbauer study for the alloy system Fe0.7?x Si0.3Mn x , where 0≤x≤0.3. Mössbauer spectroscopic results show that...     

Atmospheric corrosion of mild steel in Oman

A systematic study has been made of the initial corrosion products which form on mild steel capons exposed near the coastal region of Oman and at some industrial areas. The phases and compositions of the products formed at different periods of exposure were examined by using Mössbauer spectroscopy (295 and 78 K) and X-ray diffraction (XRD) techniques. The results show that lepidocorcite and maghemite are early corrosion products and goethite starts to form after 2 months of metal exposure to the atmosphere. Akaganeite is an early corrosion product but it forms in marine environments only, which reflects the role of chlorine effect in the atmosphere. The 12 months coupons showed the presence of goethite, lepidocorcite and maghemite, but no akaganeite being seen in the products of one of the studied areas.     

Spectroscopic and structural investigations of the ferrous and ferric high-spin state of a “picket—fence” porphyrinato acetato iron complex. A refined model for the P460 center of hydroxylamine oxidoreductase

Mössbauer investigations were performed in the ferrous and ferric form of the ‘picket-fence’ porphyrinato acetato iron complex |Fe(CH₃CO₂) (TP_pivP)|^1?,0 at temperatures varying from 1.5–200K and in fields of 0–6.2T. The ferrous complex has an unusually large quadrupole splitting, ΔE_Q=+4.25mms^?1. The quadrupole splitting in the ferric species, ΔE_Q=+1.1mms^?1, is as normally found in ferric high-spin iron porphyrins. Spin-Hamiltonian analysis of the magnetic spectra yields zero-field parameters D=?0.9mms^?1, E/D=0.33 and magnetic hyperfine parameters A_x,y=?17T, A_z=?13.3T in the ferrous high-spin (S=2) complex, and D=7.5cm^?1, E/D≈0 and A_x,y,z=20T in the ferric high-spin (S=5/2) species.     

Mössbauer and X-ray investigation of model compounds for the P460 center of hydroxylamine oxidoreductase from nitrosomonas

The divalent high-spin iron in the P460 center of hydroxylamine oxidoreductase and in three possible “picket fence” heme models exhibit extremely large quadrupole splittings (∼4 mms⁻¹). Their isomer shifts of about 1 mms⁻¹ are consistent with the X-ray results of two of the models, i.e. that Fe(II) is pentacoordinated. The coordination geometry of iron deviates considerably from the common fourfold symmetry of the “picket fence” porphyrin due to a CH₃CO ₂ ⁻ ligand. This feature is also reflected by the significant anisotropies of g-factors, A tensor and rhombicity E/D.     

Magnetic and Mössbauer studies of pure and Ti-doped YFeO 3 nanocrystalline particles prepared by mechanical milling and subsequent sintering

Single-phased nanocrystalline particles of pure and 10 % Ti ⁴⁺-doped perovskite-related YFeO ₃were prepared via mechanosynthesis at 450^°C. This temperature is ～150–350 ^°C lower than those at which the materials, in bulk form, are normally prepared. Rietveld refinements of the X-ray diffraction patterns reveal that the dopant Ti ⁴⁺ ions prefer interstitial octahedral sites in the orthorhombic crystal lattice rather than those originally occupied by the expelled Fe ³⁺ ions. Magnetic measurements show canted antiferromagnetism in both types of nanoparticles. Doping with Ti ⁴⁺ lowers the Néel temperature of the YFeO ₃ nanoparticles from ～ 586 K to ～ 521 K. The Ti ⁴⁺-doped YFeO ₃ nanoparticles exhibit enhanced magnetization and coercivity but less magnetic hyperfine fields relative to the un-doped nanoparticles. The ⁵⁷Fe Mössbauer spectra show ～ 15 % of the YFeO ₃ nanoparticles and ～22 of Ti ⁴⁺-doped YFeO ₃ ones to be superparamagnetic with blocking temperatures < 78 K. The broadened magnetic components in the ⁵⁷Fe Mössbauer spectra suggest size-dependent hyperfine magnetic fields at the ⁵⁷Fe nuclear sites and were associated with collective magnetic excitations. The ⁵⁷Fe Mössbauer spectra show the local environments of the Fe ³⁺ ions in the superparamagnetic nanoparticles to be more sensitive to the presence of the Ti ⁴⁺ ions relative to those in the larger magnetic nanoparticles.     

A structural and Mössbauer study of Y3Fe5O12 nanoparticles prepared with high energy ball milling and subsequent sintering

The influence of ball milling and subsequent sintering of a 3:5 molar mixture of Y₂O₃ and α-Fe₂O₃ on the formation of nanocrystalline Y₃Fe₅O₁₂ (YIG) particles is studied. Pre-milling the mixture for 100 h lowers the onset temperature at which the material forms to 900°C which is 200°C lower than that reported when a similar mixture of reactants was premilled for shorter times. A single-phased nanocrystalline Y₃Fe₅O₁₂ phase develops as a sole product when the pre-milled mixture is heated at 1,000°C (12 h). This temperature is ~300–400°C lower than those used to prepare the material conventionally. The bulk and surface crystal structure of the nanoparticles is studied with X-ray diffraction, Mössbauer spectroscopy, Atomic Force Microscope (AFM) and X-ray photoelectron spectroscopy.     

57Fe Mössbauer spectroscopy study of phlogopite megacrysts from an evolved carbonatitic kimberlite in the northeastern Oman Mountains

The Fe oxidation degree determined by ⁵⁷Fe Mössbauer spectroscopy and microprobe was used to characterize fresh and altered phlogopite megacrysts from an evolved carbonatitic kimberlite from northeastern Oman. The Quadrupole splitting (QS) varies between 2.19 and 2.48 mm/s (Fe^2?+?) in the fresh phlogopite samples and between 2.40 and 2.47 mm/s in the altered phlogopite samples. The quadrupole splitting of the Fe^3?+? doublets varies between 0.66 and 0.85 mm/s in the fresh samples. The altered phlogopite samples show three Fe^3?+? doublets; the first show a quadrupole splitting between 0.97 and 1.13, the second quadrupole splitting varies between 0.24 and 0.46 mm/s and the third varies between ??0.23 and ??0.35 mm/s. The phlogopite was observed to have an average Fe^3?+?/Fe_total of 35% to 37%, and corresponds to fresh phlogopite. The second one results from the alteration of the first type, and the Fe^3?+?/Fe_total ranges between 40% and 57%. Tetrahedral Fe^3?+? ions were confirmed in the altered phlogopite samples. Quantitative Fe site distributions can be obtained from room-temperature Mössbauer data if the different recoilless factors for octahedral Fe^2?+? and tetrahedral Fe^3?+? are considered. The observed isomer shifts are consistent with Mössbauer temperatures of 330 K, reported in the literature for tetrahedral and octahedral Fe^3?+? and Fe^2?+? in phlogopite. The results are compared to those obtained for natural and synthetic phlogopite from worldwide.     

The Formation of Lithiated Ti-Doped α-Fe2O3 Nanocrystalline Particles by Mechanical Milling of Ti-Doped Lithium Spinel Ferrite

Perturbed Angular Correlation method has been used to study the hyperfine magnetic field in the Heusler alloy Pd₂MnSb(Sn). Ion implantation of the recoil ¹¹¹In nuclei following heavy ion nuclear reactions ¹⁰⁸Pd(⁷Li, 4n)¹¹¹In and ¹⁰⁸Pd(⁶Li, 3n)¹¹¹In has been used to great advantage in the present case resulting in large implantation efficiency. Only a few hours of irradiation time with moderate beam current of the order of 400–500 nA resulted in sufficient implanted ¹¹¹In activity on the sample for good quality measurements. The hyperfine field was measured at ¹¹¹Cd probe nuclei substituting Mn and Sb(Sn) sites as a function of temperature. The fraction of ¹¹¹Cd nuclei occupying Mn atom sites was found to increases with the annealing of sample at higher temperatures.     

Identification of Corrosion Products Due to Seawater and Fresh Water

Hyperfine Interactions - Mössbauer and X-ray diffraction (XRD) measurements were performed on corrosion products extracted from the inner surface of two different metal tubes used in a...