Heat capacity of a five-coordinated iron(III) complex,chlorobis(N,N-dimethyldithiocarbamato) iron(III), between 0.4 and 300 k: New finding of a magnetic phase transition

The heat capacity of the title complex, Fe[S₂CN(CH₃)₂]₂Cl, has been measured between 0.4 and 300 K. A λ -type phase transition with a small shoulder arising from magnetic ordering was found at (0.609 ± 0.005) K. The character of the ordered phase has been suggested to be ferromagnetic on the basis of comparison between the methyl- and ethyl-homologues. The magnetic hyperfine structure of the Mössbauer spectra and the line broadening due to electronic relaxation effects at 1.2 K hitherto reported are concluded to result from a critical slowing-down when the magnetic transition temperature is approached from the high-temperature side. A Schottky-type anomaly arising from the zero-field splitting of a single ferric ion was observed around 2 K. The excess entropy beyond the lattice contribution at low temperatures amounts to (14.05 ±0.27) J K^?1mol^?1, which cannot be accounted for solely by the magnetic entropy of Rln 4 (= 11.53 JK^?1mol^?1) for the intermediate spin of $\text{S =}\text{3}\text{2}$. Two possibilities concerning additional conntribution have been discussed; one is a mixing of spin species of $\text{S =}\text{5}\text{2}$ and the other is a tunnel-splitting of the rotational levels of four methyl-constituents. The present study cannot give a definite conclusion as to the existence of dimeric units suggested from Mössbauer spectroscopy.     

One-dimensional magnetism in N2H6FeF5,

A new Fe(III) fluoride N₂H₆FeF₅ has been investigated by magnetic susceptibility measurements and Mössbauer resonance. It has a one-dimensional magnetic behaviour. The intrachain exchange integral ($\text{J}\text{k}\text{= -10.2}\text{K}$) has been determined by fitting the χ^-1 = f(T) curve and the ratio between the inter- and intrachain exchange integrals evaluated with Oguchi's formula. Below T_N = 9 K, N₂H₆FeF₅ shows a long range three-dimensional anti-ferromagnetic ordering.     

Doping of polyacetylene with tin chloride - Mössbauer,EPR and Raman spectroscopic studies

Polyacetylene film, containing varying amounts of trans isomer, has been chemically oxidized with SnCl₄. The reaction product has been studied by Mössbauer spectroscopy. The results suggest the existence of SnCl₅^? as the inserted species. From the temperature dependence of the recoil-free fraction the Mössbauer lattice temperature, θ, was estimated as 95K. This low value of θ indicates a significant mobility of SnCl₅^? ions at RT. Raman and EPR results are consistent with the Mössbauer effect measurements. Upon doping a broad ($\text{Δ}\text{Hpp}\text{= 5}\text{G}$) EPR line, which is a super-position of the lines characteristics of all trans polyacetylene and cis-rich polyacetylene, is transformed into a narrow ($\text{Δ}\text{Hpp}\text{= 0.8}\text{G}$), slightly assymetric ($\text{A}\text{/}\text{B}\text{= 1.23}$) line characteristic of partially oxidized trans-(CH)_x chain of high conductivity. The same doping induced isomerization can also be evidenced by Raman spectroscopy showing the disappearance of cis-(CH)_x modes after the oxidation.     

Proprietes magnetiques et etude par effet Mössbauer du thiosilicate Fe2SiS4

Fe₂SiS₄$\text{(a = 12,407}\text{A}\text{?}\text{, b = 7,198}\text{A}\text{?}\text{, c = 5,812}\text{A}\text{?}$, space group Pnma) has the olivine structure; the ferrous ions are located in two kinds of sites: one half in planes of mirror symmetry m, the other half in centers of symmetry. 1?.The magnetic study of this compound by means of magnetization measurements and Mössbauer effect, indicates from 127 K an antiferromagnetic arrangement along oy for the m sites, and an induced partial order of the same kind for the 1? sites. At 33 K, the Fe²⁺ spins in 1? sites are completely ordered and at the same time takes place a rearrangement of the magnetic structure. The observed complex model is analogous to that of Fe₂GeS₄, i.e. antiferromagnetic along 0x and ferrimagnetic along Oz.     

Mössbauer and magnetic studies of BaVS3 and V5S8 doped with 57Fe

Iron can be easily introduced in BaVS₃ and V₅S₈. It is located at the vanadium sites and has been used as a probe to analyse by Mössbauer effect the magnetic properties of its surrounding matrix. The electronic state of iron in this matrix has also been studied. It was found that in BaVS₃, the iron is in a low spin Fe³⁺ configuration $\text{(S =}\text{1}\text{2}\text{)}$. In V₅S₈ at 4.2 K, the iron is in low spin Fe²⁺ configuration (S = 0). The rapid decrease of quadrupole splitting observed between 50 and 200 K is attributed to a thermally activated change in electronic structure. The high temperature configuration (above 200 K) seems to be neither pure low spin Fe³⁺ nor high spin Fe²⁺, but a mixture of configurations fluctuating at a rate which is faster than the characteristic time of Mössbauer measurements.     

Hyperfine structure of Γ6 electronic level in cubic Yb compound from Mössbauer spectroscopy

The hyperfine structure of the Γ₆ electronic level in the cubic compound Cs₂NaYbCl₆ has been observed from the Mössbauer studies of ¹⁷⁰Yb. The effective hyperfine coupling constant is found to be $\text{-10.9±0.1}\text{mm}\text{sec.}$     

Magnetic properties and 57Fe Mössbauer effect in Lu6Fe23 and Lu6Fe23H8

Hydrogen absorption in the cubic compound Lu₆Fe₂₃ ($\text{a}\text{= 11.936}\text{A}\text{?}$) leads to a ternary hydride of the composition Lu₆Fe₂₃H₈ ($\text{a}\text{= 12.072}\text{A}\text{?}$). The H₂ take-up causes a slight increase in the saturation magnetization corresponding to an increase in Fe moment from 1.54 /u_B to 1.64/u_B per atom. The hydrogen absorption did not lead to a substantial change in the linewidth of the ⁵⁷Fe Mössbauer spectrum. On the basis of the Mössbauer data it was inferred that the H atoms occupy the f-type interstitial holes characterized by a tetrahedron formed of three Lu atoms and one Fe atom. The decrease in hyperfine field upon charging was correlated with an increase in Curie temperature.     

Temperature dependence of the hyperfine field in amorphous Fe2O3

Mössbauer spectroscopy was used to follow the hyperfine field at ⁵⁷Fe nuclei in amorphous Fe₂O₃. The value of H_hf at T = 0, 470 kG, indicates $\text{J}\text{=}\text{5}\text{2}$ for the Fe ions, while the reduced hyperfine field versus reduced temperature closely follows a $\text{J}\text{=}\text{1}\text{2}$ Brillouin function. This result is at variance with theoretical predictions for a spin glass and is also different from amorphous metals with a high content of magnetic ions as reported in the literature. Paramagnetic Mössbauer spectra of amorphous mixed oxides of Fe₂O₃ with ZnO and CoO show that the ⁵⁷Fe nuclei in all amorphous ferric oxides studied so far are coordinated in a manner similar to the d site in β F₂O₃, and distinctly different from the coordination in their crystalline form.     

Mössbauer spectroscopic studies of defect structure and alloying effects in nanostructured materials

Mössbauer spectroscopy provides spectral information from both ordered and structurally disordered regions of a solid and is therefore well suited for the atomic-scale characterisation of materials with very high defect concentrations. This applies especially to nanocrystalline materials where 5–50% of the atoms may be located at planar defects such as grain boundaries. In this paper, the range of Mössbauer spectroscopy in exploring the structure of nanostructured materials will be discussed in the form of case studies dealing with (i) nanometer-sized antiphase domains in the intermetallic compound Fe_3?x Si_1+x , (ii) ball-milling induced structural changes and alloying effects in dilute Al(⁵⁷Fe) and Y(⁵⁷Fe) alloys, and (iii) the Mössbauer signature of grain boundaries in nanocrystalline W(⁵⁷Fe).     

Long-lived non-equilibrium population of Fe3+ electronic states after the K-capture of 57Co

Mössbauer emission spectra of a frozen aqueous solution of ⁵⁷CoCl₂ show contributions from the $\text{S}{}_{\mathrm{z}}\text{= +}\text{5}\text{2}$ and the $\text{S}{}_{\mathrm{z}}\text{= +}\text{3}\text{2}$ Zeeman levels of Fe³⁺ ions at T = 4.2 K in H ? 30 kG. The K-capture results in a non-equilibrium state of relaxation time comparable to the lifetime of the nuclear excited state (～ 10^?7 s).     

Mössbauer spectroscopy study of iodine and tellurium atoms in solid argon

Mössbauer effect studies were performed on the nucleogenic ¹²⁵Te and ¹²⁹I monomers formed by the decay of their respective parents ^125mTe and ^129mTe embedded in solid argon at 4.2 K. Rare-gasmatrix-isolation (RGMI) and ion implantation techniques were combined to produce those extremely diluted Mössbauer emitters. The ¹²⁵Te spectrum is composed of a quadrupole split component with splitting $\text{e}{}^2\text{qQ}\text{2}\text{= 9.2(4)}\text{mm}\text{s}$ and isomer shift $\text{IS = + 0.35(5)}\text{mm}\text{s}$, and a single line component with $\text{IS = +0.15(5)}\text{mm}\text{s}$ with respect to a ZnTe absorber. They are attributed to Te⁰ and Te^?1 species, respectively. The ¹²⁹I spectrum is composed of a single quadrupole split component with $\text{e}{}^2\text{qQ = ?685(20) MHz and IS = +0.75(4)}\text{mm}\text{s}$ with respect to a ZnTe source. This species is attributed to I⁰. Two novel single-line absorbers with high f values at RT were developed for the Te and I experiments, e.g. Mg₃TeO₆ and Na₅IO₆. Based on our results for Te⁰ and Te^?1 and on relativistic Dirac-Slater atomic calculations, a new IS calibration curve under the form of a nonlinear relationship of IS versus the number of p holes (h_p) in the closed shell configuration of 5s²5p⁶ is established for ¹²⁵Te. The IS data of the I⁰ monomer are used to refine the IS(h_p) relationship for ¹²⁹I. From these new calibration curves values are deduced for the change in mean-squared charge radius Δ〈r²〉 = 3.4(3) 10^?3fm² for ${}^{125}\text{Te and Δ〈r}{}^2\text{〉 = 19.9(7) 10}{}^{\mathrm{?3}}\text{fm}{}^2$ for ¹²⁹I, respectively. The origin of the quadrupole interaction and the experimental features of this RGMI-implantation-Mössbauer emission spectroscopy are fully discussed.     

Polarized gamma ray investigation of iron disulphide (pyrite)

Mössbauer absorption of Fe⁵⁷, for four equivalent but differently oriented sites, in naturally occuring FeS₂ (pyrite) crystals has been studied in the ideal absorber thickness, as a function of the orientation of the crystal axes with respect to the linearly polarized gamma rays from Co⁵⁷/LiNbO₃ source and the direction of the polarization. E$\text{x}$perimental peak area ratio of ～ 1 in the polycrystalline absorber and the monocrystalline absorbers is independent of the crystal orientation. The analysis of the present experiment shows that the Mössbauer fraction, f, is isotropic and that the asymmetry parameter, η, is zero.     

On the width of the central peak in the critical scattering of γ-rays by KMnF3

The energy distribution of 14.4 keV Mössbauer γ-rays scattered from the ($\text{1}\text{2}\text{1}\text{2}\text{3}\text{2}$) reflection of KMnF₃ was measured. The result limits the energy width of the central mode at 189 K (3 degrees above the transition temperature) to less than 10^-8 eV.     

Niobates et tantalates d'europium de type “Bronze de Tungsténe Quadratique”—II: Evalution Des Niveaux D'Enerige Dans La Structure

From the magnetic and electrical properties of some TTB type niobates and tantalates of Eu¹¹ with general formula Eu_xNbO₃ (0.5$\text{}\text{?}$x$\text{}\text{?}$ 0.6), Eu_0.5TaO₃ and EuBCM₅O₁₅ (M = Ta, Nb; B = Eu¹¹, Sr, Ba; C = Na, K) we have derived a schematic energy level model of Goodenough type for tungsten bronze type structure. This was found to be qualitatively in agreement with experimental results but could not account for large amounts of Eu³⁺ calculated on the basis of Mössbauer spectra. Computed electrostatic potentials in the TTB structure allowed verification of the proposed energy level diagram for Eu_0.6NbO₃. However, for Eu_0.5NbO₃ and EuBCM₅O₁₅, agreement between theoretical potentials and experimental results is obtained by ordering the Eu³⁺ ions in perovskite cages along the c axis of the structure. With three arrangements of the ordered perovskite units, it was possible to account for the amounts of Eu³⁺ found experimentally in most of the compounds.     

A cellular model for the Mössbauer isomer shift of 99Ru, 193Ir, 195Pt and 197Au in transition metal alloys

It is demonstrated that the isomer shift of Mössbauer nuclei in transition metal alloys can be quantitatively described in terms of an atomic cell model. The isomer shift ΔE, relative to the pure metal as a reference, is derived from a change in boundary conditions for the atomic cell; $\text{ΔE = PΔφ}{}^1\text{+ QΔn}{}_{\mathrm{ws}}$, where ø¹ is the electronegativity parameter, n_ws the cell boundary electron density and P and Q are constants for a given Mössbauer nucleus. For solid solutions there is in addition a relatively small size mismatch term.     

Electron localization in Fe2PO5

Fe₂PO₅ is a mixed valence compound where Fe^II and Fe^III are in face sharing octahedra with a short Fe^II - Fe^III distance, so that electron delocalization along chains parallel to the $\text{b}$ axis of the orthorhombic cell was worth to investigate. From Mössbauer experiments, carried out up to 600°C, it appears that the 4 lines spectra evolution, as regards Isomer Shift, Quadrupolar Splitting, and Linewidth, is only consistent with a localized electron pattern. This result is interpreted from the unequivalence of the 2 sites. The strong Fe^II quadrupolar splitting decrease allows the determination of the energy gap between the d_xy and d_yz-d_zx orbitals.     

Investigations of crystal and magnetic properties of the Mn5−xFexGe3 intermetallic compounds

The Mn_5?xFe_xGe₃ intermetallic compounds are investigated with X-ray, neutron diffraction, magnetometric and Mössbauer effect methods. It is found that crystal structure of x = 1 compound is of D8₈ type while the structure of x = 3, 4 and 5 compounds is of B8₂ type. All are ferromagnets with collinearly ordered atomic spins. The lattice constants are derived from X-ray diffraction patterns, while magnetometric measurements yield the Curie temperatures and Weiss constants as well as the values of magnetic moments per molecule in ferromagnetic and paramagnetics states. The distributions of Fe and Mn atoms among two non-equivalent crystal sites are determined with the neutron diffraction method and are confirmed by the Mössbauer effect measurements. The parameters of hyperfine interactions are derived from Mössbauer absorption spectra and are attributed to iron atoms in two non-equivalent crystal sites.     

Magnetic hyperfine structure of Tm2+ ions in TmTe

Magnetic dipole and electric quadrupole interactions of Tm ions in TmTe, observed by Mössbauer spectroscopy at low temperature, are similar to those for the free ion limit of the ²F_{$\text{7}\text{2}$} ground multiplet of Tm²⁺. The Tm²⁺ ions have symmetries that are noncubic.     

Spin lattice relaxation in TmNi5 above its curie temperature

The hexagonal compound TmNi₅ was investigated by means of ¹⁶⁹Tm Mössbauer spectroscopy in the temperature range 4–350 K. Above T_c=4.5 K the magnetic hyperfine interactions were found to be governed by paramagnetic relaxation. This behaviour was interpreted in terms of a stochastic spin-down model. The spin lattice relaxation time was found to follow an exponential temperature dependence.