Mössbauer study of iron sodium borosilicate glasses

Mössbauer effect and susceptibility measurements have been performed from 1.4 K up to 300 K on Na Borosilicate glasses with 4, 8, 12, 20% by weight of Fe₂O₃ content. Besides some small isolated paramagnetic Fe²⁺ species, two Fe³⁺ particle distributions coexist with some isolated Fe³⁺ ions. Attempts have been made to give a chart of the particle size distribution in all samples.     

Mössbauer studies of hyperfine fields in disordered Fe2CrAl

Heusler-like alloy Fe₂CrAl was prepared and studied. Structure determination was done by X-ray. The structure was found to conform to the B₂ type. Magnetic hyperfine fields in this sample were studied by the Mössbauer effect. The Mössbauer spectra were recorded over a range of temperature from 40 to 296 K. The Mössbauer spectra showed the co-existence of a paramagnetic part with a magnetic hyperfine portion at all recorded temperatures. Even with the distribution in the magnetic hyperfine field, the average hyperfine field follows the (T/T _c)^3/2 law. The paramagnetic part of the hyperfine field is explained in terms of the clustering of Cr atoms.     

Iron speciation of sediments from Kuhai Lake in China by Mössbauer spectroscopy

The vertical distribution of iron species in the sediments collected from Kuhai Lake was investigated in this study. Their Mössbauer spectra were composed of one sextet and four doublets ascribable to one paramagnetic high-spin Fe³⁺, two paramagnetic high-spin Fe²⁺ with different quadrupole splittings, and one diamagnetic low-spin Fe²⁺ that corresponds to pyrite (FeS₂). The distribution of pyrite was considered to reflect the climatic change during the past 2,000 years. Mössbauer spectroscopy was successfully applied to the analysis of the Kuhai Lake sediments so as to reconstruct the history of the past climate.     

Quadrupole pair order in cubic TmGa3 studied by169Tm Mössbauer spectroscopy

The cubic compound TmGa₃ was studied by¹⁶⁹Tm Mössbauer spectroscopy. Below the paramagnetic-to-antiferromagnetic first order transition we found a coexistence of a paramagnetic and a magnetically ordered phase. Above and below the quadrupolar pair ordering temperature no change in quadrupole splitting was found in the paramagnetic phase.     

Mössbauer Spectroscopic Study on Vertical Distribution of Iron Species in Sediments from Qinghai Lake,China

In this study, ⁵⁷Fe Mössbauer spectroscopy has been applied to sediments collected from Qinghai Lake in Qinghai Province, China, to investigate the vertical distribution of iron species. Their Mössbauer spectra consisted of four doublets ascribable to one paramagnetic high-spin Fe³⁺, two paramagnetic high-spin Fe²⁺ with different quadrupole splittings, and one diamagnetic low-spin Fe²⁺ that corresponds to pyrite (FeS₂). The distribution of pyrite suggested climatic changes during the past nine thousand years. It was demonstrated that the iron speciation in the salt lake sediments by Mössbauer spectroscopy can be used to reconstruct the past environment.

     

Mössbauer analysis of the firing process of the sky-green glaze of the imitative ancient Chinese Ru porcelain

The variation of the Mössbauer parameters of the imitative ancient Ru porcelain skygreen glaze with the firing conditions is studied in detail in the present paper. The Mössbauer spectra show that the sky-green glaze contains three kinds of iron minerals, i.e. the structural iron (Fe²⁺ and Fe³⁺); Fe₂O₃ and Fe₃O₄. The relative intensity of the paramagnetic peak Fe²⁺ increases and the magnetic ratio of the magnetic peak decreases with increasing temperature. Based on the variation of the quadrupole splitting (QS) of the paramagnetic peak Fe²⁺, the phase transformation characteristics of the sky-green glaze in the firing process is discussed. The coloring mechanism of the sky-green glaze and the variation of its magnetism in the firing process are also investigated in the present paper.     

Mössbauer study of CaFeO3 under external high—Pressure

⁵⁷Fe Mössbauer and X-ray diffraction measurements have been performed on a perovskite CaFeO₃ under external high pressure upto 50 GPa at room temperature using a diamond anvil cell. Above 29 GPa the⁵⁷Fe magnetic hyperfine splitting appears superimposing with usual paramagnetic pattern of CaFeO₃. Magnitude of hyperfine field is 16 T and much smaller than 33 T of typical Fe⁴⁺ in SrFeO₃ suggesting a transition from high-spin S=2 to low-spin S=1 state in CaFeO₃.     

Mössbauer spectra of iron-chromium sulphospinels with varying metal ratio

Samples of the sulphospinel FeCr₂S₄ with varying Fe/Cr ratio around the nominal composition have been investigated with Mössbauer spectroscopy. The spectra with the narrowest lines, as well as a γ-type peak in the specific heat-temperature curve at the low temperature transition previously described, were obtained for an overall composition with a small Fe deficit. The broadening often observed in Mössbauer spectra of FeCr₂S₄ samples is attributed to Fe²⁺ on octahedral sites in the spinel phase, resulting in an electric field gradient at the Fe²⁺ ions on the tetrahedral sites. The paramagnetic Mössbauer spectrum of Fe_1.06Cr_1.94S₄ is in accordance with this interpretation.     

Low temperature Mössbauer spectroscopy and magnetism of synthetic annite mica

Annite mica has a complicated magnetically ordered ground state with T_C?58K. An Fe²⁺ paramagnetic contribution persists far below T_C (down to 4.2K) and presumably corresponds to those Fe²⁺ moments that are most weakly coupled to the two-dimensional ferromagnetic backbone. The Fe³⁺ exists in at least three families of “sites” (i. e. positions on the backbone?) that give distinct spectral contributions. The low T Mössbauer spectroscopy of biotites in general is elucidated.     

Mössbauer study of spin-spin relaxation of Fe3+ ions in the presence of other paramagnetic ions

Mössbauer spectroscopy has been used to study the influence of paramagnetic ions, viz. Cu²⁺, Cr³⁺, Co²⁺ Mn²⁺, Gd³⁺ and Dy³⁺ on the spin-spin relaxation time of Fe³⁺ ions in amorphous frozen aqueous solutions. It is found that these ions shorten the relaxation time, but the effect is much smaller than suggested earlier on the basis of measurements of relaxation of Fe³⁺ in an α-Al₂O₃ matrix. It is also found that S-state ions have a greater influence on the relaxation time than other paramagnetic ions. The spectra obtained in presence of S-state impurity ions could only be fitted by allowing the individual transition probabilities to vary independently.     

161Dy Mössbauer measurements in DyBa2Cu3O7−x

Superconducting and non-superconducting samples of DyBa₂Cu₃O_7?x have been examined by Mössbauer spectroscopy down to 0.05 K. The saturated Dy³⁺ sublattice 4f shell magnetic moments and quadrupole interactions show fairly wide distributions in both samples. These are attributed to crystal field inhomogeneities. Neither the Dy³⁺ paramagnetic relaxation rates nor the isomer shifts show any evidence of coupling between Dy³⁺ and a possible conduction band.     

A Mössbauer effect study of Dy impurities in the h.c.p. metal Zr

The 86.8 keV, 2⁺ → 0⁺ Mössbauer resonance of ¹⁶⁰Dy has been employed to study the paramagnetic hyperfine (hf) structure of Dy impurities in the hexagonal transition metal Zr. From the observed hf splitting it is concluded that the crystalline electric field ground state is an almost pure $\text{J}{}_{\mathrm{<mtext>z</mtext>}}\text{= ±}\text{1}\text{2}\text{Γ}{}_7$ Kramers' doublet with g_⊥ ? g_|. The quadrupole hf interaction and the effects of paramagnetic relaxation on the ME spectrum are also discussed.     

Mössbauer study of ultrafine FeF2 particles

Ultrafine antiferromagnetic FeF₂ particles (<10 nm) were prepared by a new technique, viz, the SF₆-sensitized infrared photodecomposition of Fe(CO)₅ induced by a transversely excited atmospheric (TEA) CO₂ laser. The magnetic properties have been examined by⁵⁷Fe Mössbauer spectroscopy. At low temperatures the magnetic hyperfine field decreases faster with increasing temperature than the hyperfine field of the bulk; this behavior appears to be consistent with collective magnetic excitations. The transition between the paramagnetic and antiferromagnetic states takes place at a higher temperature and over a broader range as compared to the bulk. FeF₂ ultrafine particles are relatively sensitive to oxidation; cubic-type iron oxide is formed.     

Mössbauer Spectrometer with Novel Moving System and Resonant Detection of Gamma Rays

Temperature-dependent ⁵⁷Fe Mössbauer spectroscopy has been used to elucidate the hyperfine parameters and dynamical behavior of the metal atom in several organo-iron complexes which have one or more η⁵ P₅ ring structures as ligated groups. The spin-lattice relaxation of the (paramagnetic) one-electron oxidation products occurs on a time scale fast compared to τ_1/2 (ME) at temperatures in the range 85 < T < 320 K.     

57Co-emission Mössbauer study on diluted magnetic semiconductor TiO2 films

Rutile-type Co _x Ti_1???x O_2???d laser deposited on alumina substrate was studied after ⁵⁷Co doping, using emission Mössbauer spectroscopy. It was found that although under certain conditions (i.e., which result in high conductivity) the thin rutile layers showed magnetooptical effect, the Mössbauer probe did not reveal any magnetic splitting, but showed paramagnetic Co^3?+? (Fe^3?+?) in the films of low electric resistance. This supports that these samples have carrier induced magnetism which is also connected to the defect structure of the rutile films.     

238U Mössbauer study on the magnetic properties of uranium-based heavy fermion superconductors

We have performed ²³⁸U Mössbauer spectroscopy of uranium-based heavy fermion superconductors, UPd₂Al₃ and URu₂Si₂, in order to investigate their physical properties, mainly their magnetic properties. The slow relaxation of magnetic hyperfine interaction in a paramagnetic state and the static hyperfine field has been observed in an antiferromagnetic ordered state for each compound. The line-widths have maximum at their characteristic temperatures where their magnetic susceptibilities have maximum values.     

Mössbauer study of phase separation in Ni80 57Fe1P19 amorphous alloys

Mössbauer spectroscopy, X-ray diffractometry, scanning calorimetry and electrochemical measurements were used to study the crystallization process of Ni₈₀ ⁵⁷Fe₁P₁₉ amorphous alloys kept in melt at different temperatures before quenching. Samples were heated up to 430°C and 720°C at a rate of 20°C/min, in order to reach characteristically different stages of crystallization. Even at the same crystallization, stage the room temperature Mössbauer spectra and the X-ray differactograms were different depending on the temperature (1050°C or 1400°C) at which the samples were kept before quenching the melt. The Mössbauer spectra showed a paramagnetic component and two sextets (H=267 kOe and H=245 kOe) at 430°C while at 720°C there was only one sextet (H=267 kOe) besides the paramagnetic component. The changes in the Mössbauer spectra of different samples due to crystallization are consistent with the explanation that phase separation occurs in Ni₈₀ ⁵⁷Fe₁P₁₉ rapidly quenched from the melting temperature of 1050°C.     

57Fe and57Co Mössbauer studies of highT c Y-Ba-Cu oxides

The⁵⁷Co emission Mössbauer spectra from YBa₂Cu₃O_6.92 (1-2-307) and YBa₂Cu₃O_6.00 (1-2-306) have been measured and compared with the⁵⁷Fe absorption spectra from YBa₂Cu_2.95Fe_0.05O_7?δ in order to clarify decisively the site assignments for the⁵⁷Fe quadrupole-split doublets in these compounds. Mössbauer spectra obtained from both specimens consist of four components whose hyperfine interaction parameters well agree with each other. It is shown that the Co and Fe atoms mainly substitute at Cu1 chain sites in 1-2-307, but in 1-2-306 the Co atoms occupy randomly the Cu2 plane sites and indicate magnetically-split sextet which converts to a paramagnetic doublet of S-state Fe³⁺ in 1-2-307 by a post-annealing in O₂ gas.     

Mössbauer spectroscopic study on (Eu1−x Gd x )FeO3

Europium gadolinium ferrites (Eu_1?xGd_x)FeO₃ (X=0, 0.2, 0.4, 0.6, 0.8) are synthesized. The results of the X-ray diffraction show that all the compounds possess a perovskite structure. Both the¹⁵¹Eu Mössbauer spectra and the⁵⁷Fe Mössbauer spectra are measured. The¹⁵¹Eu Mössbauer spectra are considered to be the pure quadrupole spectra. The results show that the isomer shift and the quadrupole splitting of the¹⁵¹Eu spectra vary with x. The hyperfine filed of the⁵⁷Fe Mössbauer spectrum depends on the unit-cell volume. The⁵⁷Fe spectra of the samples synthesised by the high-pressure and high-temperature mothod show a part of paramagnetic structure.     

Valencies of manganese and iron ions in cubic ferrites as observed in paramagnetic Mössbauer spectra

The ground state of the ionic system Mn²⁺+Fe³⁺Mn³⁺+Fe²⁺ on octahedral sites in a spinel lattice is investigated on paramagnetic materials with specially chosen compositions. The valencies are established by means of the very different Mössbauer spectra of divalent and trivalent iron. Divalent iron is found to be unstable in the presence of trivalent manganese contrary to ?im?a's widely accepted model.A sample of ZnFe_1·75Ti_0·25O₄ shows at room temperature an Fe³⁺, Fe²⁺ spectrum, in which divalent and trivalent iron are indistinguishable, and at 78°K the superposition of a similar spectrum and a ferrous spectrum.