Magnetic properties of ferrihydrite

The magnetic properties of a sample of synthetic ferrihydrite have been investigated by use of Mössbauer spectroscopy. The area ratios of the Mössbauer lines are not significantly changed by application of magnetic fields at 5 K, indicating an amorphous magnetic structure. An average magnetic moment per particle of 3.1×10^?21 JT^?1 was estimated from the dependence of the hyperfine splitting of the Mössbauer spectra on external magnetic fields at 80 K.     

The Mössbauer research community: A report

The Mössbauer research community has gone through various stages of development in its 30⁺ year history. Signs of maturity of the Mössbauer effect is shown in the number of experimental applications, the number of Mössbauer transitions that are available and the large number of scientists that have been and are involved with Mössbauer research. In recent years, there has been a significant increase in the number of publications using Mössbauer Spectroscopy to investigate both amorphous and high temperature superconductor materials. This overall growth in the Mössbauer scientific literature has been 6–7% per year since 1984, while during the preceding period there was no increase in the number of publications per year. The Mössbauer Effect Data Center continues to make use of the various developing technologies in the area of computers and communications. The Center recently completed a ten-year project of bringing together all its databases into one computer system. Also, the Center has recently completed the development of a new approach to the dissemination of information by making available subsets of the Mössbauer database on PC computer disks. The future of the Data Center will focus significant attention on networking strategies with the Mössbauer research community.     

Characterization and pH stability of insoluble products of the reaction between cyanide and ferrous sulphate

X-ray diffraction (XRD), infrared (IR) spectroscopy and⁵⁷Fe Mössbauer effect spectroscopy were used to characterize and monitor the pH stability of cyanide and ferrous sulphate reaction mixtures. Limited information was obtained from the XRD and IR measurements because of the amorphous nature of the samples. The Mössbauer studies show that considerable changes occur when there is an increase in pH at which the sample is prepared. Prussian-blue type compounds and iron oxide in the form of small particles crystallize out at low and high pH values, while additional complexes are formed at intermediate pH values of 6 to 9.⁵⁷Fe Mössbauer effect spectroscopy is thus a powerful technique for monitoring the environmental stability of cyanide waste streams that result when modern methods of extractive metallurgy of gold are employed on mineral ores.     

Mössbauer and magnetic studies of nanocrystalline zinc ferrites synthesized by microwave combustion method

Zinc ferrite nano-crystals were synthesized by a microwave assisted combustion route with varying the urea to metal nitrates (U/N) molar ratio The process takes only a few minutes to obtain Zinc ferrite powders. The Effect of U/N ratio on the obtained phases, particle size, magnetization and structural properties has been investigated. The specimens were characterized by XRD, Mössbauer and VSM techniques. The sample prepared with urea/metal nitrate ratio of 1/1 was a poorly crystalline phase with very small crystallite size. A second phase is also detected in the sample. The crystallite size increases while the second phase decrease with increasing the urea ratio. The saturation magnetization and coercivity of the as prepared nano-particles changed with the change of the U/N ratio. The powder with the highest U/N ratio showed the presence of an unusually high saturation magnetization of 16 emu/g at room temperature. The crystallinity of the as prepared powder was developed by annealing the samples at 700 ^°C and 900 ^°C. Both the saturation magnetization (Ms) and the remnant magnetization (Mr) were found to be highly dependent upon the annealing temperature. Mössbauer studies show magnetic ordering in the powder even at room temperature. The Mössbauer and the magnetic parameters of this fraction are different from the standard values for bulk zinc ferrite.     

Mössbauer and magnetic studies of nanocomposites containing iron oxides and humic acids

A sample of volcanic ashes emanated from the Osorno volcano, southern Chile, was characterized with X-ray fluorescence, X-ray diffraction and ⁵⁷Fe Mössbauer spectroscopy, in an attempt to identify the iron-bearing minerals of that geologically recent magmatic deposit. X-ray patterns indicated that the sample is mainly constituted of anorthite, Fe-diopside-type and Ca-magnetite. The crystallographic structures of these dominant iron minerals are proposed on basis of their chemical composition and corresponding Mössbauer data to support models refined by fitting powder X-ray diffraction data with the Rietveld algorithm.     

Magnetic and Mössbauer spectroscopic studies of NiZn ferrite nanoparticles synthesized by a combustion method

The properties of nanocrystalline Ni_0.5Zn_0.5Fe₂O₄ synthesized by an auto-combustion method have been investigated by magnetic measurements and Mössbauer spectroscopy. The as-synthesized single phase nanosized ferrite powder is annealed at different temperatures in the range 673–1,273 K to obtain nanoparticles of different sizes. The powders are characterized by powder X-ray diffraction, vibrating sample magnetometer, transmission electron microscopy and Mössbauer spectroscopy. The as-synthesized powder with average particle size of ~9 nm is superparamagnetic. Magnetic transition temperature increases up to 665 K for the nanosized powder as compared to the transition temperature of 548 K for the bulk ferrite. This has been confirmed as due to the abnormal cation distribution, as evidenced from room temperature Mössbauer spectroscopic studies.     

Mössbauer study of amorphous alloys irradiated with energetic heavy ions

The Mössbauer spectroscopy was applied to study radiation damage in metal-metalloid amorphous alloys irradiated with⁴⁰Ar/E=225 MeV/ or¹³²Xe/E=120 MeV/ ions at room temperature. The observed dose dependent changes in the intensity of the Mössbauer lines and of the hyperfine field distributions can be associated with structural changes in short-range order of the irradiated amorphous alloys.     

Mössbauer diffraction and interference studies of polycrystalline metals and alloys

After a review of previous work on Mössbauer diffraction and interference phenomena, the principles of the kinematical theory of Mössbauer diffraction are presented. The emphasis is on how the spectroscopic capabilities of the Mössbauer effect can be used to advantage in diffraction studies on materials and condensed matter. Experimental results from Mössbauer powder diffractometry experiments are presented. These results identify the difficulties of Mössbauer powder diffraction experiments, but also demonstrate that a unique chemical environment selectivity is possible for Mössbauer diffraction. Future experiments with Mössbauer powder diffraction require the development of efficient detectors, and some possibilities are suggested.     

Irradiation effects in amorphous alloy Fe80B20

The Mössbauer effect has been used to study the irradiation effects in the amorphous alloy Fe₈₀B₂₀ after 40 keV helium ion bombardment. Conversion electron Mössbauer spectroscopy reveals the eminent irradiation effects; α-iron phase appears in the damaged region of the sample.     

Nanocrystalline iron-based alloys investigated by Mössbauer spectrometry

Nanocrystalline alloys exhibit great fundamental and technological interests because of their microstructural properties, and their excellent soft magnetic properties. ⁵⁷Fe Mössbauer spectrometry is a well suitable technique to investigate Fe-based nanocrystalline alloys: its local probe behaviour permits to elucidate the nature of hyperfine interactions at different resonating iron nuclei and to distinguish their immediate atomic surroundings. We review on the recent Mössbauer developments performed on first FeCuMBSi and then FeCuBSi nanocrystalline alloys. From Mössbauer studies, one can estimate the crystalline (i.e., amorphous) fraction, the Si-content in Fe--Si nanocrystalline grains emerging from amorphous alloys of the first series, the temperature dependence of magnetic behaviours of both crystalline and amorphous phases; finally, we present a novel fitting procedure applied to FeCuBSi nanocrystalline alloys which result from bcc-Fe crystalline grains embedded in an amorphous matrix. In this case, the hyperfine structure is able to model the intergranular phase.     

Goldanskii-Karyagin effect in FePS3

Mössbauer studies have been performed on FePS₃ in powder form between 125 K and 450 K. The Mössbauer spectrum consists of an asymmetric doublet, ratio～0.93 at room temperature. The asymmetry is attributed to the Goldanskii-Karyagin effect and the lattice anisotropy is found to be ～1.4, with the largest vibrations parallel to thec ^? axis of the monoclinic unit cell. The Debye temperature is ～200 K.     

Mössbauer investigation of Fe−Zr amorphous alloys hydrogenated after annealing

Transmission and conversion electron Mössbauer spectroscopy were used in order to get further information bout thé effect of hydrogenation in Fe₈₉Zr₁₁ amorphous alloys in connection with the observation that the magnetically split spectrum appearing at room temperature due to a moderate hydrogenation gradually collapses with increasing hydrogen content. The Mössbauer measurements were performed on differently hydrogenated amorphous samples aged at 150 °C 300 °C and 600 °C before the hydrogenation. The time dependence of hydrogenation has also been measured. From the changes of Mössbauer parameters depending on the annealing temperature as well as on the cathodic potential of hydrogenation (compared with the hydrogen concentration measured by gas chromatography) we can conclude that relaxation processes and structural changes, taking place in these amorphous alloys, influence the hydrogen uptake, already at relatively low temperatures.     

Mössbauer effect investigation of amorphous FeZr interlayers formed by solid state reaction

Recent investigations claimed the complete amorphization of elemental FeZr multilayer films by solid state reaction during vacuum annealing. In the present study it is established by⁵⁷Fe conversion electron Mössbauer spectroscopy (CEMS) that annealing under ultrahigh vacuum conditions does not lead to complete amorphization: only a maximum thickness of ≈14 Å interfacial α-Fe is transfered into the amorphous phase between 620–660 K. This thin amorphous layer apparently acts as a diffusion barrier and prohibits further growth of the amorphous phase. The average composition of the amorphous interfacial layer was determined from the Mössbauer spectral parameters.     

A Mössbauer study on TiBaCa3(Cu1−xFex)3O8.5 superconductors

Two main superconducting phases, 1223 and 2223 in TiBaCa₃Cu₃O_8.5 superconductor, are identified by powder x-ray analysis and⁵⁷Fe Mössbauer spectroscopy analysis. The Mössbauer fitting results shown that iron atoms in the lattice substitute two inequivalent sites of copper atoms for each main phase. The temperature dependence of Mössbauer parameters are obtained, and several problems are discussed which relate to the electric charge transfer which takes place around the superconducting transition temperature, the lattice dynamics and the effect on oxygen deficiency at different temperatures.     

Transparency of a thin absorber in Mössbauer optics with allowance for electron relaxation

A model of Mössbauer absorption in the nuclear level anticrossing regime with allowance for electron relaxation has been proposed. The role of quantum interference in the creation of particular transparency on Mössbauer transitions under these conditions has been determined and the dependence of this characteristic on the relaxation and mixing parameters has been obtained using the stochastic theory of Mössbauer relaxation spectra.     

Magnetic insulator glasses

An outline is given of the use of Mössbauer spectroscopy as a probe of the amorphous structure and magnetic coordination in magnetic insulator glasses. Using the⁵⁷Fe Mössbauer resonance as an example in the context of amorphous ferric oxides and fluorides, the manner in which both paramagnetic and hyperfine-field-split spectra can be analyzed is presented. Emphasis is given to the information contained in Mössbauer lineshapes and linewidths in addition to the more obvious line-position data. A number of general findings are set out for ferric speromagnetics with particular references to Mössbauer studies of amorphous Fe₂O₃, Y₃Fe₅O₁₂ (YIG), FeF₃ and NaFeF₄.     

Mössbauer studies of iron-rich metallic glasses

Iron-based metallic glasses have recently become an important class of ferromagnetic materials exhibiting excellent soft magnetic properties coupled with good mechanical properties. These glasses are usually prepared by rapid quenching techniques and are produced in thin long ribbon form with widths ranging from a few mm to 150 mm or more.⁵⁷Fe Mössbauer spectroscopy has been extensively used to study hyperfine interaction parameters in these metallic glasses to understand ferromagnetism in amorphous structure. In particular, Mössbauer spectra have been carefully analyzed to reveal information about the distribution of hyperfine fields resulting from the randomness of the atomic arrangement and to understand the temperature dependence of hyperfine fields, spin-wave excitations, magnetic structure, thermal stability and crystallization, the quenched-in magnetization axis, the Curie temperature and its dependence on compositions, the effect of stress and pressure on the magnetic properties, corrosion behaviour, local order and atomic arrangement, phase transformation, etc. This paper reviews the application of⁵⁷Fe Mössbauer spectroscopy to magnetic studies on metallic glasses mainly based on the iron-boron alloy system, and some of the significant results obtained which are characteristic of the glassy/amorphous state.     

Mössbauer spectroscopy in studying magnetite formed by iron- and sulfate-reducing bacteria

The kinetics of iron mineral formation by thermophilic dissimilatory iron reducing bacteria using Fe(III) amorphous hydroxide and acetate CH₃COO^? as an electron acceptor and donor, respectively, was investigated by Mössbauer spectroscopy. The effects of various physical and chemical conditions and the presence of an inert organic substance on the formation of biogenic minerals were considered. The production of magnetite due to microbial sulfate reduction by hyperthermophilic dissimilatory sulfate-reducing microorganisms was investigated by Mössbauer spectroscopy methods.     

Documentation and evaluation of Mössbauer data for minerals

More than 2,500 Mössbauer spectroscopic studies on minerals have been published since 1960. These papers contain approximately 8,000 sets of Mössbauer mineral data on at least 400 different minerals. This information has been compiled into a database that includes isomer shifts, quadrupole splittings, and magnetic hyperfine interactions at room, liquid nitrogen, and liquid helium temperatures. The database provides a profile of the Mössbauer research performed to date on minerals, including type and locality of minerals investigated, significance of the studies and results, and location of the research facilities. The data and information are available both in printed and magnetic form. With the establishment of this resource, the Mössbauer Effect Data Center has begun a systematic evaluation of the Mössbauer mineral data. It is anticipated that this resource can be used for the identification of minerals as powder X-ray diffraction data is.