ESR and Mössbauer studies of the precipitation process of various ferrites from silicate glasses

ESR and Mössbauer studies of the precipitation process of various ferrites from silicate glasses were made to characterize the precipitation mechanism. The changes in linewidth (H _1/2) and effectiveg-value (g _eff) in the ESR spectra of the precipitation process are well explained in terms of super-exchange interaction between magnetic ions and interparticle dipolar interaction between precipitated ferrites. The precipitation tendency of spinel type ferrites from silicate glasses was found to be in the following order: NiFe₂O₄CoFe₂O₄>Fe₃O₄ZnFe₂O₄, MnFe₂O₄. The above order coincided with the order of octahedral site preference energies of divalent transition metal ions.     

The121Sb Mössbauer spectra of antimony-containing glasses

The¹²¹Sb Mössbauer spectra of a series of Na₂O-B₂O₃-Sb₂O₃, (Na₂O, 2P₂O₅) + Sb₂O₃, and (Na₂O, 2SiO₂) + Sb₂O₃ glasses have been measured. The chemical isomer shifts,, and the quadrupole couplings,eQV _zz, for antimony (III) in different glasses have been estimated. From the changes of isomer shift is has been deduced that the ionicity of the Sb-O bond increases with decreasing Na₂O content in Na₂O-B₂O₃-Sb₂O₃ glasses; and when the network former is changed, with equivalent molar composition, the ionicity of the Sb-O bond increased in the order borate silicate < phosphate.     

Magnetic properties of Cu-Cd ferrite investigated by Mössbauer spectroscopy

Samples of the copper-cadmium ferrite series Cd _x Cu_1–x Fe₂O₄ (x=0 to 1) have been investigated by means of Mössbauer spectroscopy at 77 K. Mössbauer spectra forx=0.0 to 0.7 suggest the existence of two hyperfine fields, one due to the Fe³⁺ tetrahedral ions (A-sites) and the other due to the Fe³⁺ octahedral ions (B-sites), while forx=0.8 it shows relaxation behaviour and forx0.9 it exhibits a paramagnetic quadrupole doublet. The systematic dependence of the isomer shifts, line widths, quadrupole interactions and nuclear magnetic fields of⁵⁷Fe³⁺ ions in both A and B sites has been determined as a function of cadmium content. The variation of nuclear magnetic fields at the A and B sites is explained on the basis of the A-B and B-B supertransferred hyperfine interactions. Analysis of the average Mössbauer line widths as a function of cadmium concentration suggests that the relaxation spectrum observed atx=0.8 (77 K) is possibly due to domain wall oscillations. It has been found here that QS (B) increases from CuFe₂O₄to CdFe₂O₄ as the cadmium concentration is increased.     

Mössbauer studies of O4+-bombarded Nb3Sn

Mössbauer spectra have been taken for Nb₃Sn films on Hastelloy substrate bombarded with 25-MeV O⁴⁺ ions at fluences of 9.6 × 10¹⁵ and 4.0 × 10¹⁶ cm^–2, and annealed at temperatures up to 1050 C. The bombarded samples are found to contain highly damaged Nb₃Sn and Nb₆Sn₅, and show superconducting transitions at 7.3 and 3.3 K, respectively. Annealing at higher temperatures does not restore the properties of the samples to those known for undamaged Nb₃Sn films. The results rather indicate the presence of Nb₃Sn and also Nb₆Sn₅ even after annealing at 850 C. Annealing at 1050 C seems to produce only regions of heavily damaged Nb₃Sn.On leave from North Dakota State University, Fargo, North Dakota.     

Structural properties and Mössbauer spectroscopy of Finemet™ doped with Ge

Structural and magnetic properties of amorphous and crystalline alloys Fe_73.5Cu₁Nb₃B₉Si_13?xGe_{x=1;5;10;13.5} were studied by means of energy dispersive X-rays (SEM + EDX), X-ray diffraction (XRD), differential scanning calorimetry (DSC), Mössbauer spectroscopy (MS), as-quenched (a-q) and after annealing (a). EDX show agreement between the nominal and the measured atomic contents for all alloys. DSC provided three phase transition temperatures of the materials, MS spectra reveal amorphous structure of as-quenched alloys and a mixture of amorphous and crystalline structures of annealed alloys. The XRD spectra of annealed alloys allow us to resolve three crystalline phases of Fe.     

Wet chemical synthesis of iron pyrite and characterization by Mössbauer spectroscopy

Iron pyrite in powder form was synthesized by using FeCl₃ and either thiourea or Na₂S as the starting materials. Attempts were made to achieve pure pyrite phase through a simple wet chemical reaction in the liquid state followed by high temperature annealing in the argon atmosphere. The phase purity and the composition of the sample were determined by X-ray diffraction (XRD) and energy dispersive analysis of X-ray (EDAX), respectively. The phase purity and its intrinsic magnetic behavior were further clarified by Fe⁵⁷ Mössbauer spectroscopic investigations.     

Mössbauer studies of a-Fe74Co10−xCrxB16 alloys

Fe⁵⁷ Mössbauer spectroscopy has been employed to study hyperfine interactions in melt-spun a-Fe₇₄Co_10–x Cr _x B₁₆ (x = 0, 2.5, 5, 7.5 and 10) ribbons. The Curie temperature and the effective hyperfine fields observed for the spectra at 80 K show a systematic fall with increasing chromium content. Increasing chromium content also brings about a change in the orientation of the magnetization axis in that it comes closer to the direction of -ray propagation. The temperature dependence of hyperfine fields in a-Fe₇₄Co₅Cr₅B₁₆ alloy is accounted for using the existing theoretical models. The field distribution curves show a temperature dependence, while the e.f.g. distribution evaluated from the paramagnetic doublet spectra aboveT _c are temperature independent. The spin-wave coefficients B (B_3/2) and C (C_5/2) and the critical exponent, , were determined and their significances explained.     

Susceptibility,magnetization and Mössbauer studies of the Mg-Zn ferrite system

The variation of susceptibility with temperature of the Zn _x Mg_1–x Fe₂O₄ system has been obtained between 300 K and the Neél temperature at a constant magnetic field of 7.0 Oe for x=0.0 to 0.7. Through the magnetization measurements of this Mg-Zn ferrite system the variation of saturation magnetization with zinc concentration was determined in gaining information about the Yafet-Kittel angles in the system for x0.9 at 298 K. The observations indicate the existence of a Yafet-Kittel type of magnetic ordering in the system. A molecular field analysis of the Y-K spin ordering using a three sublattice model is shown to explain the experimental data satisfactorily. For the sake of verification, Neél temperatures of Mg-Zn ferrites were also determined from Mössbauer studies.     

Mössbauer studies on an AISI 1137 type steel

An AISI 1137 type medium carbon steel was studied by means of scanning electron microscopy and Mössbauer spectroscopy. This steel in as received state at room temperature was ferritic. Different heat treatments on related steel exhibited different microstructures such as pearlite and bainite. Also magnetism of these product phases was determined as 32-7 T and 32-6 T relatively where ferromagnetism of ferritic phase in as received state was 3305 T. Mössbauer parameters such as isomer shifts and % volumes were also determined before and after transformations.     

Mössbauer study of bacterial ferrihydrite

Mössbauer measurements reveal four inequivalent Fe sites in ferrihydrite produced by Klebsiella oxytoca. The origin of these sites can be understood in terms of two nanosized structural regions in the bacterium and a certain ordering of bilayers and single layers of Fe-occupied octahedra.     

Mössbauer study of maghemite nanoparticles

Mössbauer spectroscopy has been used to study maghemite (γ-Fe₂O₃) particles with average dimensions on the microscopic (～1 μm, “bulk” state) and nanoscopic (15 and 20 nm) levels. Data provided by this method on the thickness of a surface region of magnetic nanoparticles and features of their magnetic state have been analyzed. It is suggested that the proposed approach is promising for a large number of nanomagnetic materials.     

Application of Mössbauer spectroscopy to studying steel corrosion at nuclear power plants

Methodical aspects of applying Mössbauer spectroscopy to studying corrosion in ultrathin layers of steels in contact with coolant water of nuclear power installations are considered. A new procedure is developed for measuring Mössbauer spectra of surface layers of steels at grazing incidence of the Mössbauer γ-radiation on the surface of pearlite and austenite steels. New data are obtained on the phase composition of nanometer-thick surface layers of “metallic” steel samples. Corrosion products occurring in pipelines such as the pressurizer pipe and steam generator tubing of nuclear power plants with water-cooled water-moderated reactors are studied.     

Emission Mössbauer spectroscopy of V2O5 doped with 57Co

A Mössbauer study of V₂O₅ doped with carrier-free ⁵⁷Co showed that the iron produced by the nuclear decay of cobalt can be stabilized in different forms depending on the temperature conditions of the sample treatment. Components of di- and trivalent iron were identified in the spectra of the V₂O₅ melt solidified under the conditions of slow cooling. After quenching the melt by immersing the crucible in mercury, a component with an isomer shift of -0.53(2) mm s^?1, corresponding to the oxidation state of +5, appears in the spectrum.     

Size-evolution towards metallic behavior in nano-sized gold and platinum clusters as revealed by 197Au Mössbauer spectroscopy

Four types of molecular Au₅₅ clusters, with different types of ligands, have been studied using ¹⁹⁷Au Mössbauer spectroscopy. Emission Mössbauer measurements were also performed on the larger Pt309 cluster, in which ¹⁹⁷Au was produced by neutron activation. There is a large influence of the ligands on the charge densities at the surface atoms of the metal atom cluster cores. For the Au₅₅ clusters, the inner core atoms have a different charge density at the nucleus than the bulk metal, and it depends also slightly on the type of ligands on it. For the Pt₃₀₉ compound, the inner core atoms have the same charge density at the nucleus as in the corresponding bulk metal. We, therefore, conclude that the inner core of the Pt₃₀₉ cluster is metallic with respect to the electronic charge densities, while this is not yet the case for the Au₅₅ cluster.