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To investigate the interactions of 57Fe atoms with sulfur hexafluoride SF6 molecules, in-beam Mossbauer spectra were measured for 57Mn implanted SF6 at 9 K and 65 K. Isolated 57Fe atoms or ions produced by β-decay were not trapped within the SF6 matrix. At 9 K, monomeric FeF2 and FeF3 molecules were produced by reaction of 57Fe with F atoms released by decomposition of the SF6 molecules. When the temperature of the SF6 solid was increased to 65 K, FeF4 was formed in addition to FeF2 and FeF3. Density functional calculations were performed to confirm the assignments of the candidate species identified in the Mossbauer spectra.

Iron nitrides with a high nitrogen content are metastable and can be prepared in the form of fine particles or as a film. An arc discharge of iron metal in a reactive atmosphere provides a convenient method to produce iron-based films. In this study, iron nitride films were formed on an aluminum substrate by arc deposition of iron in a nitrogen atmosphere under a controlled nitrogen flow rate (10–30 sccm). The samples were analyzed by transmission Mossbauer spectroscopy and X-ray diffraction. When the temperature of the aluminum substrate during deposition was maintained at 298 K, e-Fe3-2N was obtained for nitrogen flow rates in the range 20 to 30 sccm. When the aluminum substrate was heated to 573 K during deposition with nitrogen flow rates of 15 to 30 sccm, a highly crystalline e-Fe2N film was formed.

Metastable iron carbide thin films (χ-Fe5C2 and o-Fe7C3) were produced by pulsed laser deposition of Fe in a CH4 atmosphere, and their Mossbauer spectra and X-ray diffraction patterns were measured. Films consisting of amorphous Fe-C carbide were obtained when the substrate temperature was kept at 300 K during deposition, while crystalline films were produced for a substrate temperature of 573 K. The effect of CH4 pressure was investigated. Films produced below 4.0 Pa consisted of a combination of χ-Fe5C2 and α-Fe, and single-phase carbide films were produced at higher pressure: pure χ-Fe5C2 and o-Fe7C3 films were produced at 4.0 and 6.0 Pa, respectively. At 13 Pa, a film was produced consisting of o-Fe7C3 and paramagnetic amorphous Fe-C containing a large amount of C atoms. The film produced at the highest pressure of 40 Pa consisted solely of paramagnetic amorphous Fe-C.

Mn-doped feroxyhyte (δ-FeOOH) nanoparticles were synthesized using a wet chemical method, starting from a mixture of iron and manganese salts. The particles obtained were needle-like, around 100 nm in length, and formed had a nano-urchin structure. The compositions of the four samples obtained were calculated to be δ-Fe0.92Mn0.08OOH, δ-Fe0.75Mn0.25OOH, δ-Fe0.56Mn0.44OOH, and δ-Fe0.32Mn0.68OOH. The superparamagnetic behavior of the nanoparticles was determined from their room-temperature Mossbauer spectra. The hyperfine magnetic field of the Mn-doped δ-FeOOH nanoparticles decreased when iron atoms were substituted by Mn atoms. Furthermore, Mn atoms were locally doped into δ-FeOOH.

In-beam Mossbauer spectroscopy of 57Fe using a short-lived 57Mn (T1/2 = 89 s) implantation was applied to study the chemical products of localized Fe atoms in ethylene and acetylene matrices at low temperatures. The spectra obtained in both matrices were analyzed as three doublets. In ethylene at 14 K, Fe(C2H4)2 (Fe0, S = 1), [Fe(C2H4)3]+ (Fe+, S = 3/2), and [Fe(C2H4)2]+ (Fe+, S = 3/2) were assigned as derived from the Mossbauer parameters and density functional theory calculations. On the other hand, the products of [Fe(C2H2)2]+ (Fe+, S = 3/2) and [(C2H2)FeCCH2]+ (Fe+, S = 3/2) were determined in the acetylene matrix at 17 K.

Synchrotron-Radiation-based $^{\mathrm {149}}$ Sm Mossbauer spectroscopy was applied to Sm intermetallics, SmBe13 and SmTi2Al20. Temperature dependence of the Mossbauer parameters in SmBe13 indicate the Sm valence state is purely trivalent. SmBe13 also showed second-order Doppler shift in synchrotron-radiation-based $^{\mathrm {149}}$ Sm Mossbauer spectroscopy. The Mossbauer parameters obtained in SmTi2Al20 suggest that the Sm valence is fluctuating and the magnitude of the magnetic moment is reduced by hybridization between 4f and conduction electrons and/or effect of crystal electric field.

Laser ablation in liquid is a useful mean of producing nanoparticles, based on both laser ablation (LA) and laser irradiation (LI) effects. In order to investigate the mechanism by which iron carbide nanoparticles are generated in ethanol, iron carbide nanoparticles were produced by LA of an iron block in a flowing ethanol solvent, which enabled separation and collection of the nanoparticles immediately following the process. These same particles were subsequently subjected to LI while suspended in stagnant ethanol. Both the LA and LA/LI nanoparticles were assessed using Mossbauer spectroscopy, X-ray diffraction and transmission electron microscopy. LA in flowing ethanol was found to produce nanoparticles composed of cementite (Fe3C) and other metastable iron carbides with an average size of 16 nm, dispersed in amorphous carbon. LI of the LA nanoparticles suspended in ethanol increased the particle size to 38 nm and changed the composition to pure Fe3C.

Zinc-iron oxide nanoparticles (ZnxFe3−xO4 and δ-ZnxFe1−xOOH) were successfully synthesized by room temperature chemical reaction of a solution containing ZnCl2 and FeCl2 in the presence of gelatin. The composition of products could be controlled by variation of the Zn/Fe mixture ratio of the starting material. ZnxFe3−xO4 nanoparticles were obtained from a solution with a high Zn/Fe ratio, whereas Zn-doped feroxyhyte (δ-ZnxFe1−xOOH) nanoparticles were obtained from a solution with a low Zn/Fe ratio. The ZnxFe3−xO4 nanoparticles were spherical with diameters of approximately 10 nm, and the δ-ZnxFe1−xOOH particles were needle-like with lengths of approximately 100 nm. Mossbauer spectra measured at room temperature indicated superparamagnetic behavior of the nanoparticles, whereas the magnetic components were observed at low temperature. The Zn content of the intermediate species ( $(\text {Zn}^{\text {II}}_{\mathrm {x}}\text {Fe}^{\text {II}}_{\mathrm {1-x}}\text {Fe}^{\text {III}}_{\mathrm {2}}\mathrm {O}_{4})$ ) plays an important role in the oxidation process. When the Zn concentration was high, the content of Fe2+ in the intermediate species was small, and Zn2+ prevented further oxidation of the nanoparticles. When the starting material had low Zn concentration, the amount of Fe2+ in the intermediate species became large and was rapidly oxidized into δ-ZnxFe1−xOOH while rinsing under the ambient atmosphere.

A mixture of silver and iron oxide nanoparticles were synthesized by the reaction of FeSO4, AgNO3, and N2H4 in the presence of gelatin at room temperature. The silver/iron oxide nanoparticles were subsequently examined using powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and Mossbauer spectroscopy. TEM observations revealed two distinct sizes of nanoparticles. The small nanoparticles with diameters of less than 10 nm were assigned to maghemite, and the large particles with diameters of approximately 20 nm were assigned to metallic silver. A Mossbauer spectrum of the maghemite nanoparticles at room temperature showed superparamagnetic behavior due to the small particle sizes. The Mossbauer spectrum measured at low temperature showed a magnetic sextet and a component of distributed hyperfine magnetic fields (DHMF). The DHMF component corresponded to the surface or defects of the maghemite nanoparticles. Silver enhanced the production of maghemite nanoparticles, and the size of the maghemite particles could be controlled by varying the amount of silver salt.

An amorphous iron/carbon mixture was prepared by sonolysis of ferrocene in diphenylmethane. Heating of the amorphous mixture at 900 or 1200 °C produced nanoparticles, which were then analyzed using Mossbauer spectroscopy, X-ray diffraction, and transmission electron microscopy.

Iron(III) sulfide Fe2S3 particles were produced using a polyol method. Although pyrrhotite Fe1−xS appeared together with Fe2S3, the relative yield of Fe2S3 changed when the concentration of reagents in the oleylamine changed. Mossbauer spectra of the particles showed superparamagnetic doublets due to Fe2S3 at 293 K, along with a hyperfine magnetic splitting of H = 24.7 T at 6 K. XRD patterns of the Fe2S3 suggested a structure similar to that of greigite Fe3S4.

A new detector system for the coincidence technique between Mossbauer γ-rays and energetic β-rays originating from 57Mn has been developed for in-beam Mossbauer spectroscopy using 57Mn implantation. This system enables time-resolved Mossbauer measurements of 57Fe at various elapsed times after β−-decay of 57Mn with sufficient quality. We applied this system to the time-dependent measurement of the site distributions of dilute Fe atoms in n-type Si. It was suggested that Fe atoms were already located at substitutional and interstitial positions in Si within a time of about 100 ns after the β−-decay of 57Mn, and that the occupancy ratio between these positions was hardly dependent on the elapsed time after the β−-decay.

The in-beam Mossbauer spectrum of 57Mn implanted into a Xe solid at 14 K was measured. Four singlets were observed in the spectrum, assigned to 57Fe + (3d7), 57Fe + (3d64s1), 57Fe0 (3d64s2), and 57Fe0 (3d74s1). The assignments were in agreement with calculated electron densities at nuclei reported in the literature. The β-decay of 57Mn did not disturb the surrounding Xe lattice, showing a singlet peak, and the excited states were stabilized in the time range of the Mossbauer measurements of ~100 ns. The production mechanism was explained in terms of the reduction of 57Mn x + and 57Fe y + ions by free electrons in the Xe matrix.

The reaction products of isolated single iron atoms in a low concentration matrix of ethylene were studied using in-beam Mossbauer spectroscopy with a short-lived 57Mn (T 1/2=1.45 m) beam. The in-beam Mossbauer spectrum of 57Fe arising from 57Mn in a matrix of ethylene and argon measured at 16 K was analyzed with four components. Density functional theory calculations were carried out to confirm the assignments. It was suggested that the reaction produced monoiron species of Fe(C 2 H 4) with a spin state of S = 2.

Iron carbide nanoparticles were synthesized by laser ablation of iron in alcohols (methanol and ethanol). A new cell, designed to allow the ablation to be conducted in a flowing solvent, enabled separation and collection of the nanoparticles immediately after production, thus preventing further photochemical reactions of the colloids. The nanoparticles were investigated using Mossbauer spectroscopy, X-ray diffraction, and transmission electron microscopy. In methanol, they consisted of α-iron, γ-iron, iron carbide, and amorphous paramagnetic iron carbides, whereas in ethanol they consisted of iron carbides and amorphous paramagnetic iron carbides. The difference in products depending on the alcohol was attributed to the different carbon supplies for methanol and ethanol. For both solvents, the average particle size was found to be 16 nm, and the nanoparticles were dispersed in amorphous carbon. We also examined the effect of further laser irradiation of the colloids using stagnant solvent, and the particle size was found to increase and a very small amount of carbonization was observed.

Copper ferrite nanoparticles were synthesized via the oxidation of precipitates obtained from the reaction of FeCl2, CuSO4 and N2H4 in the presence of gelatin. These copper ferrite particles were subsequently examined using powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and Mossbauer spectroscopy. The average size of the copper ferrite nanoparticles was less than 5 nm, and they exhibited superparamagnetic behavior as a result of their small size. The low temperature Mossbauer spectrum exhibited three sets of sextets, two corresponding to the tetrahedral and octahedral sites of the copper spinel structure and one with small hyperfine magnetic field corresponding to the surface or defects of the nanoparticles. When the ratio of copper salt was increased, the tetrahedral site became preferable for copper, and metallic copper and copper ferrite were both present in a single nanoparticle.

Iron films were deposited on porous alumina substrates using an arc plasma gun. The pore sizes (120 – 250 nm) of the substrates were controlled by changing the temperature during the anodic oxidation of aluminum plates. Iron atoms penetrated into pores with diameters of less than 160 nm, and were stabilized by forming γ-Fe, whereas α-Fe was produced as a flat plane covering the pores. For porous alumina substrates with pore sizes larger than 200 nm, the deposited iron films contained many defects and the resulting α-Fe had smaller hyperfine magnetic fields. In addition, only a very small amount of γ-Fe was obtained. It was demonstrated that the composition and structure of an iron film can be affected by the surface morphology of the porous alumina substrate on which the film is grown.

Highly energetic 57Mn (T 1/2 = 1.45 m) was generated by nuclear projectile fragmentation in a heavy-ion accelerator, and implanted into lithium hydride (LiH) and lithium deuteride (LiD) at 578 K. Mossbauer spectroscopy with β − γ coincidence detection was then carried out on the 57Fe obtained from β −decay of the 57Mn to study the time dependence of the site distributions and coordination environments of dilute Fe atoms implanted in the LiH and LiD. The results suggest that the Fe atoms can substitute for either the Li and H or D atoms within 100 ns. Additionally, the displacement behavior of the substitutional 57Fe atoms on the lattice sites is discussed.

In-beam Mossbauer spectra of 57Fe after 57Mn (T1/2= 1.45 min) implantation into a CH 4 matrix and mixture matrices of CH 4 and Ar at 18 K were measured. The spectrum obtained in the CH 4 matrix was analyzed well with a doublet and a singlet peaks. These components were assigned to two constitutional isomers of Fe(CH 4)\(_{\mathrm {2}}^{\mathrm {+}}\) as derived from density functional theory calculations and the Mossbauer parameters. In the case of the low concentration of CH 4 with an Ar matrix, the Fe + (3d 74s) in the excited state atomic configuration and Fe + (3d 64s 1) in the ground state were observed, as observed in our previous implantation experiment into Ar and Xe matrices. The formation yields of Fe(CH 4)\(_{\mathrm {2}}^{\mathrm {+}}\) are discussed in term of the number of first-nearest-neighbor CH 4 molecules around an Fe + ion.

Ferromagnetic nanoparticles of iron and vanadium co-doped SnO2 were synthesized by a sol-gel method. Fe and V co-doped SnO2 enhanced the magnetization, which showed the maximum saturation magnetization (Ms) at 1 % of Fe and 1 % of V co-doping. With further increasing the amounts of Fe and V co-doping into SnO2 host, the Ms decreased. Chemical states of vanadium ions were deduced as V5+ states by x-ray absorption spectroscopy. Mossbauer spectrometry revealed that the intensities of sextet components are related to the Ms, which indicates that small amounts of Fe and V co-doping is effective to enhance Ms.

A single-phase γ‴-FeN film with the rock-salt structure was produced by pulsed laser deposition of Fe onto an Al substrate in a N2 atmosphere. Its Mossbauer spectra and powder X-ray diffraction patterns were measured. γ‴-FeN was found to be antiferromagnetic exhibiting a hyperfine magnetic field of 30 T at a temperature of 5 K. It was found to have a Neel temperature of 220 K. A minor component with a higher hyperfine magnetic field of 49 T at 5 K was also observed. It is thought to originate from defects in γ‴-FeN.

Aluminium oxides doped with 1% 57Fe were prepared by sol-gel method, and annealed for 3 hours at various temperatures between 550°C and 1100°C. Amorphous phases were obtained below 1000°C, and crystalline α–Al2O3 was formed at 1100°C. Although Al2O3 itself shows diamagnetism, the light doping of Fe ions into aluminium oxide induced a very weak ferromagnetism, but the ferromagnetism disappeared by longer annealing. Mossbauer spectra were composed of paramagnetic Fe2 + and Fe3 + species for samples heated below 750°C, and of paramagnetic Fe3 + above 850°C, in addition to a magnetic sextet and relaxation peaks of Fe3 + . The magnetic and quadrupole interactions of the sextet and the relaxation peaks and the density functional calculations suggest that the lightly doped Fe3 + ions are substituted at Al sites in the Al2O3 lattice.

1–5% Fe and 1% Co co-doped SnO2 samples were synthesized by sol-gel method. Their magnetization increased with increasing crystal size of rutile SnO2. Their Mossbauer spectra contain a broad sextet, magnetic relaxation components, and paramagnetic doublet peaks for less than 3% Fe doping. The sextet of α-Fe2O3 was observed instead of magnetic relaxation peaks for Fe doping of above 4%. The broad sextet and relaxation components may be related to the magnetic properties of Fe and Co co-doped SnO2.

Iron films were produced by pulsed laser deposition (PLD) of iron in Ar gas and Mossbauer spectra of these films were obtained at room temperature. The orientation of the hyperfine magnetic field was found to vary depending on the pressure of the Ar gas. Iron films produced at low Ar pressures exhibited magnetic fields parallel to the substrate surface. The magnetic field became increasingly perpendicular to the substrate with increasing Ar pressure. Collisions with Ar gas molecules reduced the translational energies of laser-evaporated iron atoms and thus the orientation of crystals formed on the substrate varied depending on the Ar pressure.

We measured the temperature dependence of 57Fe Mossbauer spectra obtained after 57Mn implantation into polycrystalline LiH with an extremely low implantation dose. Density functional calculations suggested that the Fe atoms were predominantly implanted into both Li and H substitutional sites of the LiH crystal.

Laser ablation of iron in an organic solvent (pentane, hexane, or decane) was performed using an air-tight cell to produce iron carbide nanoparticles. Mossbauer spectra of the nanoparticles were obtained at room temperature. They revealed that the nanoparticles consisted of two paramagnetic components and magnetic components. The two paramagnetic components were a high-spin Fe(II) species and an amorphous iron carbide containing a large amount of carbon. Whereas the magnetic components measured at room temperature exhibited superparamagnetism, those measured at low temperature were fitted by a combination of four sextets, which were assigned to Fe7 C 3. The Fe7 C 3 yield was higher in higher molecular weight solvents. Transmission electron microscopy (TEM) images of the samples showed that the nanoparticles were spherical with diameters in the range 10–100 nm.

Iron nitride films were produced by pulsed laser deposition of Fe onto an Al substrate in an N2 atmosphere and their Mossbauer spectra and powder X-ray diffraction patterns were measured. The nitrogen content of the iron nitride films varied depending on the N2 pressure. Under high N2 pressures, γ”-FeN (ZnS structure) and γ’”-FeN (NaCl structure) were obtained. The yields of these two phases could be controlled by varying the Al substrate temperature. γ”-FeN and γ’”-FeN were found to be paramagnetic and antiferromagnetic, respectively, at 5 K.

Pulsed laser deposition of iron atoms on graphite substrates was performed to produce iron carbide films. Mossbauer spectra of the sample revealed that iron carbide was produced on the substrate surface and that an α-Fe layer was produced above the iron carbide layer. When the substrate temperature was maintained at 300 K, the iron carbide layer had a hyperfine magnetic distribution because it contained high density of defects. Laser deposition of Fe at 570 K produced cementite Fe3C with fewer defects due to enhancement of thermal reactions or annealing of the films. The orientation of hyperfine field of the Fe3C film was parallel to the substrate surface.

A new detection system was developed using a gas-filled resonance counter operated in anticoincidence with a plastic scintillation detector for 57Fe Mossbauer spectroscopy using a short-lived 57Mn (T1/2 = 1.45 min) beam. We have succeeded in measuring 57Fe Mossbauer spectra obtained after 57Mn implantation into single-crystalline α-Al2O3 at 92, 193, and 298 K, with an adequate ratio of the resonance peak against the background by applying this detection system, in spite of the extremely low implantation dose. Final positions of Fe atoms in α-Al2O3 are discussed and compared with the results of the ab initio density functional calculations.

Samples of SnO2 doped with different amount of Fe (10–20%) and Sb (5–25%) were prepared by sol–gel method. Room temperature ferromagnetism was found to increase as a result of co-doping with Sb, as compared to SnO2 doped only with Fe. 57Fe Mossbauer spectra of almost all samples exhibited two paramagnetic doublets and a small subspectrum referring to magnetic relaxation at room temperature. Only the samples Sn0.65Fe0.2Sb0.15O2 − δ and Sn0.85Fe0.1Sb0.05O2 − δ with 4 h long annealing time showed well developed sextets and larger magnetic coercivity compared to that of the other samples. The sextet observed was considered to be due to precipitates like Sn doped α-Fe2O3. The results suggest that the origin of the magnetic interactions is enhanced by the presence of magnetic defects, which can interact with the iron ions by free carrier electrons. For the sample with precipitates, the grain boundary defects may play an important role of enhanced ferromagnetism.

Iron films produced using an arc plasma gun were studied by Mossbauer spectroscopy, and their surface features were examined using atomic force microscopy and scanning electron microscopy. The surface morphology of the iron films reflected the morphology of the substrates. When an aluminum foil with 100-nm grooves was employed as the substrate, the surface of the iron film also had grooves. The nuclear spin orientation of the iron tends to be linear along the grooves. The effects of deposition conditions on nuclear spin orientation, including the groove size on the aluminum substrates, the iron film thickness, and the temperature during deposition, were studied.

Emission Mossbauer spectra of 57Fe arising from the 56Fe(n, γ)57Fe reaction in two crystal forms of iron disulfide were measured at room temperature and liquid nitrogen temperature. Both forms exhibited two doublets assignable to the parent material and the new species produced by the nuclear reaction. At low temperature three doublets explained the spectra obtained. Production of thermally unstable species after the neutron capture reaction was suggested.

Reaction of laser-evaporated iron atom was investigated by Mossbauer spectroscopy and was applied for the production of films. Iron oxide films were produced by laser-deposition of Fe metal and hematite solid onto Al substrates, and the compositions of the films changed depending on the pressure of the O2 atmosphere and the temperature of the substrates. The spin orientations of α-Fe films deposited by three types of deposition methods were compared. The nuclear spin of iron films produced by deposition of Fe atoms vaporized by resistive heating was perpendicular to the substrate surface, while that of films produced by laser-deposition of Fe was parallel to the substrate surface. The nuclear spins of iron films produced using an arc-plasma-gun were linear orientations along nanometer-sized grooves on the Al substrate surface.

Iron oxide (γ-Fe2O3) and iron carbide (Fe3C) particles were produced by the polyol method. Ferrocene, which was employed as an iron source, was decomposed in a mixture of 1,2-hexadecandiol, oleylamine, and 1-octadecene. Particles were characterized using Mossbauer spectroscopy, X-ray diffraction, and transmission electron microscopy. It was found that oleylamine acted as a capping reagent, leading to uniform-sized (12-16 nm) particles consisting of γ-Fe 2O3. On the other hand, 1-octadecene acted as a non-coordinating solvent and a carbon source, which led to particles consisting of Fe3C and α-Fe with various sizes.

An in-beam emission Mossbauer spectrum of 57Fe arising from the 56Fe(n, γ) 57Fe reaction in iron disulfide at room temperature was measured with a parallel plate avalanche counter. It was clearly observed that the nuclear reaction and the following process lead to the production of a new chemical species of iron different from the parent compound.

The in-beam Mossbauer spectroscopy using a short-lived 57Mn (T 1/2=1.5 min) beam was carried out to study the production of the exotic chemical species of 57Fe atoms arising from 57Mn implanted into solid oxygen. The obtained spectra can be analyzed by four components of doublets at least, which are assigned to be novel Fe species of FeO, Fe(O2), (O2)FeO2, and Fe(O2)2, on the basis of ab initio molecular orbital calculations.

Iron thin films deposited on Al foil by pulsed laser ablation were characterized by con­version electron Mossbauer spectrometry (CEMS). The hyperfine fields became large and the isomer shift was closed to that of bulk α-Fe with increasing the thickness of deposited films. The small grains are so reactive that small particles of FeIII oxides were produced in thin deposited layers. The magnetic orientation of the deposited films became from parallel to in-plane to at random. The small grains were considered to grow by aggregating with ablation time.

Laser-ablated iron atoms and fine particles were isolated in low-temperature Ar matrices, and their chemistry was studied by means of Mossbauer spectroscopy. Reaction of Fe with O2 produces Fe-O, O-Fe-O, and Fe-O2 as isolated in Ar matrices. On annealing the sample, unstable species are converted to more stable species in the matrix. Similarly, Fe-O and O-Fe-O were obtained from the reaction of iron atoms with N2O. Furthermore, Fe-N was found to be produced by the reactions of laser-ablated Fe with N2.