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We present a study of the magnetic properties and the [sup.57]Fe Mossbauer spectra of the [Hf.sub.1-x][R.sub.x][Fe.sub.6][Ge.sub.6], R = Gd and Dy, series. The macroscopic magnetic measurements are consistent with the magnetic independence of the R and Fe sublattices. However, the [sup.57]Fe Mossbauer study reveals a more complex magnetic behavior. Specifically, below [T.sub.t] [approximately equal to] 100 K a spin reorientation takes place in Hf[Fe.sub.6][Ge.sub.6]. The analysis of the corresponding Mossbauer spectra shows that below [T.sub.t] a fraction of the iron moments is canted from the c-axis. The substitution of Hf by Gd or Dy reduces the fraction of canted iron moments. The hyperfine magnetic fields are found to decrease upon the R = Gd or Dy substitution. This effect can be qualitatively explained as a result of the decrease in the hybridization between the d valence states of the R element with the 3d iron states. Index Terms--1-6-6 compounds, magnetic materials, Mossbauer spectroscopy.

The magnetic behavior of dextran-coated magnetite F[e.sub.3][O.sub.4] nanoparticles with median particle size (d)=8 nm is studied. It is proposed that these particles have bulklike ferromagnetic structure with ordered A and B sublattices, but nearly compensated the magnetic moments.

Research has been conducted on Mn(II) systems, a similar magnetically coupled Fe(III) (sub)9 complex and Zn(II) (sub)9, (Pb(II) (sub)3) (sub)2 and Fe(III) (sub)5 derivatives with the ligands. The structures, magnetic properties amd Mossbauer data of these structures are reported.

Research delineates the use of 1,10-phenanthroline in Fe(sup)III carboxylate reactions leading to the production of three new tetranuclear iron(III)/phenanthroline complexes. The core structure of two of the title complexes show the tetranuclear cluster arranged in a 'butterfly' fashion. All three exhibit magnetic properties.

The rubredoxin from Clostridium pasteurianum shows good fits to an S+2 spin Hamiltonian for the (sup)5D manifold of iron(II) of the protein. The spin-Hamiltonian characteristics are in agreement within the (sup)5D theoretical predictions. Data indicate that the torsions for the reduced rubredoxin seem to be the same within 2 degrees for the whole cell and purified protein.

Infrared (IR) spectra in the OH stretching region and Mossbauer spectra (MS) have been acquired for natural tourmalines from magmatic and hydrothermal deposits in the state of Minas Gerais, Brazil. In the magmatic environment, samples of tourmaline were collected from granitic pegmatites and granitoids. In the former, the elbaite-schorl series is prevalent, while in the latter the schorl species is dominant. Tourmalines from hydrothermal gold deposits are typically intermediate members of the dravite-schorl series, whereas the uvite and Fe-bearing uvite species are present in tourmaline samples from a magnesite deposit. Different behaviors are discussed in terms of local lattice environment, geological history, fluid/rock interaction or magma evolution, and degree of crystallinity.

Research has been conducted on the dinuclear (Fe (super)II, Gd (super)III) complexes. The crystal and molecular structures of these complexes have been explored and the results are reported.

Research has been conducted on the Ba (sub)2 FeO (sub)4 and Ba (sub)3 FeO (sub)5 crustals. The characterization of these crystals carried out via the use of the single-crystal X-ray diffraction, magnetic measurements and Mossbauer spectroscopy is described.

Dark pyroxene crystals found in a calcite vein cutting across marbles and skarns at Andranondambo, southern Madagascar, were investigated with various techniques in order to characterize and identify the mineral phase. Methods applied include powder X-ray diffraction, thin-section microscopy, electron-microprobe analysis, densimetry, and thermogravimetry coupled to mass spectrometry (TGA-MS), FTIR, and Mossbauer spectroscopy. The chemical composition of the mineral phase was determined as {[Ca.sub.0.98],[Na.sub.0.03]}[[Mg.sub.0.68], [Fe.sup.2+.sub.0.07][Fe.sup.3+.sub.0.03],[Al.sub.0.16,][Ti.sub.0.04]] ([Si.sub.1.77],[Al.sub.0.23])[O.sub.6]. The refined unit-cell parameters are: a = 9.719(2) [Angstrom], b = 8.838(2) [Angstrom], c = 5.287(1) [Angstrom], [beta] = 106.05(2) [degrees], and V = 436.33(6) [[Angstrom].sup.3]. The refractive indices are: [alpha] = 1.690 [+ or -] 0.002, [beta] = 1.700 [+ or -] 0.002, and [gamma] = 1.712 [+ or -] 0.002. The density is 3.370 (55) g/[cm.sup.3]. The mean refractive index calculated from the chemical composition yields a Mandarino compatibility index of K = -0.0167. From the various analytical data, we were able to conclude that the mineral corresponds to Fe- and Ti-bearing aluminian diopside. TGA-MS data suggest the presence of calcite solid inclusions and minor [H.sub.2]O and C[O.sub.2] fluid inclusions. Chemical analyses of the calcite host matrix revealed clear rare earth element enrichment. Mossbauer spectra obtained at varying temperatures show the presence of [Fe.sup.2+] and [Fe.sup.3+]. Both exhibit broad quadrupole-splitting distributions, indicating widely fluctuating chemical and structural environments for the probe Fe nuclei. The broad temperature range (80-470 K) over which the spectra were collected resulted in a precise determination of the [Fe.sup.2+]/[Fe.sub.tot] ratio as 0.68, which is consistent with the chemical composition as determined from the microprobe analyses. For comparison, the Mossbauer spectra of two specimens of the type locality of aluminian diopside (the mineral formerly named 'fassaite') were analyzed as well and found to be consistent with those obtained for the Madagascar crystals. The relation between mineral paragenesis and local geological features is briefly discussed.

Research has been conducted on the iron(II) complexes. The development of these complexes with the FeN (sub)6 chromophore of the same ligand and differing counterions is reported and the results of the complexes' crystal and molecular structure analysis are reported.

Analysis of electron delocalization and spin ordering in the mixed-valence binuclear iron complexes shows a correlation between these two electronic properties and their dependence on the metal-metal separation. Data also point out fast electron hopping on the Mossbauer time scale.

Research explores synthetic routes to the nitrogenase clusters demonstrating that the molybdenum-iron-sulfur fragment is a topological analogue of enzymes P-cluster. Data further reveal structural aspects of another cluster whose core consists of the above three metal cuboidal units bridged and connected by mu2-sulfur and iron bond respectively.

Research demonstrates metal-metal interactions in terms of electrochemical and redox reactions, MMCT spectroscopy, the magnetic moments, and Mossabauer measurements of the trinuclear complexes of iron-phthalocyanine-iron systems. Data identify one of the complexes as Prussian Blue.

Research has been conducted on [Fe(btzp) (sub)3](ClO (sub)4) (sub)2. The crystal structure of the compound and its magnetic and Mossbauer properties have been investigated.

Research has been conducted on the biotin and lipoate synthases. The results of Mossbauer studies of (super)57 Fe-reconstituted biotin synthase are presented.

Research was conducted to determine the electronic structure of the five iron centers of the intact cytochrome bf using EPR and Mossbauer techniques. Mossbauer data indicate the presence of four iron sites with the additional site revealed by EPR analysis.

A study was conducted to analyze small angle neutron scattering and Mossbauer spectrometry measurements on nanocrystalline Ni3Fe. The materials were prepared using mechanical attrition. The small angle neutron scattering measurements were carried out for a range of applied magnetic fields. Experimental results indicated an increase in the grain boundary magnetic moments after a 265 degrees C annealing.

The global regulator FNR (for fumarate nitrate reduction) controls the transcription of >100 genes whose products facilitate adaptation of Escherichia coil to growth under [O.sub.2]-limiting conditions. Previous Mossbauer studies have shown that anaerobically purified FNR contains a [[4Fe-4S].sup.2+] cluster that, on exposure to oxygen, is converted into a [[2Fe-2S].sup.2+] cluster, a process that decreases DNA binding by FNR. Using 57Fe Mossbauer spectroscopy of E. coli cells containing overexpressed FNR, we show here that the same cluster conversion also occurs in vivo on exposure to [O.sub.2] Furthermore. the data show that a significant amount of the [[4Fe-4S].sup.2+] cluster is regenerated when the cells are shifted back to an anaerobic environment. The present study also demonstrates that 57Fe Mossbauer spectroscopy can be employed to study the in vivo behavior of (overexpressed) proteins. The use of this technique to study other iron-containing cell components is discussed.

The synthesis of a sulfur-bridged sandwich cubane-type molybdenum-antimony cluster compound ((H2O)9Mo3S4SbS4Mo3(H2O)9)(pts)8*24H2O from the incomplete cubane-type molybdenum cluster (Mo3S4(H2O)9)(super 4+) and antimony metal is described. The existence of the core was confirmed by X-ray crystallography, while 121Sb Mossbauer spectroscopy indicated that the oxidation state of antimony in 2*pts is III and the mean oxidation number of molybdenum is +3.5.

Direct integration of Schrodinger's equation yields the transition probability for the Mossbauer effect, assuming that the bound nucleus receives a sudden impulse of momentum from a gamma particle. Generalization from two coupled oscillators to a linear chain introduces the discrete Fourier transform, in real variables. This chain of coupled oscillators can be used to suggest how very low order collective modes can remain unexcited by the impact.

A study was conducted to analyze the 57Fe nuclear magnetic resonance chemical shielding and Mossbauer electric field gradient tensors, including their orientations for a cytochrome c model compound. The study also examined isopropyl isocyanide and carbon monoxy-myoglobin model systems and metalloporphyrins supporting bis(pyridine) and bis(trimethylphosphine) ligands. Experimental results indicated that 57Fe nuclear magnetic resonance shifts and Mossbauer quadrupole splittings in metalloporphyrin and metalloprotein system can be determined by density functional theory.

Research was conducted to examine the impact of chromium on the magnetic and structural characteristics of amorphous and nanocrystalline alloys. This study utilizes a method wherein a nanocrystalline Fe(sub 73.5)Nb(sub 4.5)Cr(sub 5)Cu(sub 1)B(sub 16) alloy is examined using radio-frequency magnetic fields and Mossbauer spectroscopy. Results revealed anisotropy field distributions in the alloy as well as a decline in magnetorestriction.

The local symmetry and electronic environment of [Fe(eta5-C5H5)(CO)x] substituted metallaborane compounds were analyzed by Mossbauer spectroscopy. The compounds based on well-resolved Mossbauer spectra exhibited the efficiency of the [mu-2,3-(P(C6H5))2B5H7- ligand as an electron donor compared to the unsubstituted [B5H8]- ligand. Furthermore, the efficiency of the borane cage of the metallaborane compounds to act as a donor ligand decreased when its size was reduced.

An analysis of Mossbauer spectra from a model complex of known structure with an Fe(super 2+)(S1=2)-muOH-Cr(super 3+)(S2=3/2) center and of its Fe(super 3+)(S1=5/2)-muO-Cr(super 3+)(S2=3/2) analog reveals that effective S(super eff) = 1/2 and S(super eff) = 1 Hamiltonians successfully reproduce 4.2 K spectra, as antiferromagnetic spin coupling between Fe and Cr ions which results in S(super eff) = 1/2 and S(super eff) = 1 was confirmed. Analysis of the 4.2K spectra from the Fe(super 2+)(S1=2)-muOH-Cr(super 3+)(S2=3/2) center in terms of a spin Hamiltonian that includes the isotropic exchange and zero-field splittings was also conducted.

The low temperature magnetization measurement of Fe/Pd multilayers prepared by ultra high vacuum electron-beam evaporation technique shows there is some interlayer coupling between the iron layers, and the temperature dependence of saturation magnetization is influenced by paladium layers. Antiferromagnetic coupling between iron layers and high magnetoresistance effect is absent for Fe/Pd multilayers. When the thickness of the paladium layer increases from 36 angstrom, the crystal structure of the iron layer changes from a body centered cubic to a face centered cubic one.

Mossbauer spectrometric analysis of metaloxides with the composition of MgFe2O4 shows that the materials are made of magnesioferrite particles having anisotropy constant similar to magnetocrystalline anisotropy. Annealing increases the particle size and the formation of the oxide, alpha-Fe2O3. Heat treatment increases the value of anisotropy constant.

A study of the Mossbauer effect and magnetic and magnetorestrictive properties of SmDyFe2 compounds at various concentrations revealed the MgCu2 cubic structure to be independent of concentration, which varied nonlinearly with the lattice constant. Magnetostriction was inversely proportional to Dy content, while magnetic moment occurred at different Sm/Dy ratios.

The electric field gradient on different Fe sites in Fe-doped 124 superconductor is calculated by the point-charge-effective-valence model. Ion valences and electronic field gradient showing the lattice displacement of Fe ion for different Fe clusters are related. Fe is displaced from CuO2 planes toward the apical O(1) site.

The point dipole model described the magnetic interactions between multicenter protein metal clusters. This model was applied to systems possessing dinuclear centers containing trapped valence metal sites. The local spin model was based on the exchange interactions between an iron site and a siroheme of a (4Fe-4S) cluster.

Transmission Mossbauer spectroscopic studies of nanocrystalline Fe-Cu-Si-B alloy structure revealed dissolved Si atoms in Fe bcc lattice. The Si atoms, which were arranged in the alpha-Fe(Si) phase exhibited short range order.

Single-crystal X-ray diffraction is used to prepare and conformationally analyze three diphosphates AM3(P2O7)2. Trans or skew edges are seen in the MO6 octahedra chains, which appear as zigzag, infinite entities in the three isostructural compounds. A three-dimensional conformation with pathways parallel to the b axis are produced when P207 groups are used to join the infinite chains. Various regions inside the pathways reveal the positioning of alkaline-earth metals. The occurrence of Fe(II) is proved by Mossbauer spectra.

The ideal Mossbauer absorber thicknesses for three micas representative of the annite-phlogopite series were calculated. A close agreement was found between the measured ideal absorber thickness values and the values produced using the simple formula previously described by Long et al, showing that their method affords an accurate way of performing such estimates. This formula was used to measure ideal 57Fe Mossbauer spectroscopy absorber thicknesses for various Fe-bearing metals. A graph for evaluating the thin absorber thickness is presented.

The iron monosulfide (FeS) was fabricated by a polyol method. X-ray diffraction (XRD) patterns show that the sample has a troilite hexagonal structure (space group P - 62c) with a lattice constant [a.sub.0] = 5.985, [b.sub.0] = 5.985, and [c.sub.0] = 11.658 [Angstrom]. The hysteresis loop with maximum applied field 10 kOe at room temperature and zero field cooling (ZFC) curve with an applied magnetic field 200 Oe at temperature ranging from 50 to 450 K measured using a vibrating sample magnetometer (VSM) show the ferrimagnetic behavior. Mossbauer absorption spectrum shows 2-sextets at room temperature, while it shows a clear 1-sextet at 4.2 K. We conclude that it has ferrimagnetic property at room temperature as pyrrhotites ([Fe.sub.1-x]S) by analysis of Mossbauer spectrum. Index Terms--[alpha] transition, Mossbauer spectroscopy, pyrrhotite, troilite.

The occurrence of ferromagnetism is studied in the Ca[Ru.sub.1-x][Fe.sub.x][O.sub.3] system by means of magnetic Compton scattering. The magnetic Compton scattering experiment revealed the occurrence of a large magnetic moment on Ru and an antiferromagnetic coupling between Fe and Ru spin moments.

Research has been conducted on the ferric peroxo complexes. The preparation of the mononuclear nonheme Fe(III)-hydroperoxo and Fe(III)-peroxo complexes in solution has been carried out and studied via the UV-visible, EPR, resonance Raman and mass spectrometry and the details are reported.

Research has been conducted on the iron(III) porphyrin complexes with weak axial ligands. Results indicate that bis(tetrahydrofuran)(2,7,12,17-tetrapropylporphycenato)iron(III) perchlorate is a pure intermediate spin complex, and the results of the Mossbauer spectroscopy, (super)1 H NMR, EPR and SQUID magnetometry are presented.

Research has been conducted on the bis(isodicyclopentadienyl)iron and the corresponding ferrocenium hexafluorophosphate. Mossbauer spectra of these complexes have been investigated.

A study was conducted to analyze Mossbauer spectra determined at 15 K from rhombohedral phase Y2Fe17Nx with intermediate N content. The spectra were determined using an Austin Science Associates constant-acceleration spectrometer with a 30 mCi source of 57Co in a rhodium matrix. Experimental results indicated that for the dumbbell 6c site, the hyperfine field values were unchanged upon nitrogenation.

A study was conducted to determine the 295 K unit cell parameters of Pr2Fe17Hx, where x is 0, 1, 2, and 3. The unit cell volume expands anisotropically upon hydrogenation. The Mossbauer spectra were determined between 4.2 and 295 K. The temperature dependence of the sit average hyperfine fields was then examined. Experimental results indicated gradual changes in the first and fifth absorption lines with increases in the hydrogen content.

A study was conducted to analyze static and dynamic contributions to the spectral broadening associated with conventional transmission Mossbauer spectra. Selective excitation double Mossbauer spectroscopy was utilized to carry out the analysis. The measurements utilized a constant acceleration spectrometer for energy detection. Experimental results indicated that chemical disorder promotes the line shapes of transmission spectra on Fe-Ni Invar alloys.

A study was conducted to analyze the structure and magnetic characteristics of the Fe(sub 80.5)Nb7B(sub 12.5) nanocrystalline alloy using Mossbauer spectroscopy. The rf-Mossbauer experiments were carried out as a function of the rf field intensity. Magnetically soft amorphous and nanocrystalline phase from the microcrystalline were determined. Results indicated a minimum coercivity of 0.15 Oe at 610 degrees C.

From our previous studies, it has been found that the Fe-Pb-O granular films which have been adequately annealed exhibit an enhanced tunneling magnetoresistance effect (TMR). The TMR effect is about 10% at room temperature, which can be claimed as the maximum value ever detected so far. In this report the TMR effect of Fe-Pb-O granular films from different annealing time have been investigated. The Mossbauer spectrometer was used to collect the information of Fe magnetic microstructure. It has been found that the tunneling barrier from the magnetic compound formed between a-[Fe.sup.2][O.sub.3] and PbO plays an important role in obtaining large TMR effect. And the non-magnetic Fe-Pb-O compounds which exist on the surface of iron granules as a thin layer and grow with annealing time seem to decrease TMR effect.