151Eu and57Fe Mössbauer effect studies of magnetic interactions in europium transition element oxides solution

The solid state solutions of europium transition element oxides Eu (Fe0.8M0.2)O₃ (M=Sc,Cr,Mn,Co) are synthesized. The X-ray diffraction of the compound shows that all the compounds possess the perovskite structures. Both the¹⁵¹Eu Mössbauer spectra and the⁵⁷Fe Mössbauer spectra are measured. The hyperfine magnetic field and non-axisymmetric electric field gradient are observed in the¹⁵¹Eu Mössbauer spectrum. The⁵⁷Fe Mössbauer spectrum shows that there are four components of hyperfine fields corresponding to four kinds of different neighbours of the Fe ion.     

Emission Mössbauer spectroscopic studies of57Fe atoms produced in57Co-labelled trinuclear cobalt-iron halogenoacetate complexes

Mixed-valence states of⁵⁷Fe atoms produced after EC-decay of⁵⁷Co in a series of trinuclear cobalt-iron halogenoacetate complexes, [Co^IIFe ₂ ^III O(CH_3?nX_nCO₂)₆(H₂O)₃] (0≤n≤3, X=Cl, Br, and I), were studied by comparing the results obtained by emission Mössbauer spectroscopy with those observed in absorption Mössbauer spectra of analogous trinuclear iron complexes, [Fe^IIFe ₂ ^III O(CH_3?nX_nCO₂)₆(H₂O)₃]. Some of the emission Mössbauer spectra show a temperature-dependent mixed-valence state as found in the absorption Mössbauer spectra. Others show a somewhat different temperature dependence compared with the absorption Mössbauer spectra. The results were interpreted in terms of after-effects of the EC-decay.     

151Eu Mössbauer studies in the high Tc superconducting oxide materials

¹⁵¹Eu Mössbauer studies have been made across the respective superconductive transition temperatures in two compounds, La_1.7Eu_0.1Sr_0.2CuO_4?y and EuBa₂Cu₃O₇, having zero resistance state at 25K and 85K respectively. The¹⁵¹Eu isomer shift data establish that Eu ions are in trivalent state at all temperatures. The Mössbauer f-factor does not show any significant anomaly across the T_C.     

Mössbauer and calorimetric studies of portland cement hydration in the presence of black gram pulse

Effect of different concentrations of naturally occurring admixture in the form of fine powder of black gram pulse (BGP) on the hydration of Portland cement was studied by isothermal calorimetry and ⁵⁷Fe Mössbauer spectroscopy. The spectra were recorded for anhydrous cement and the hydration products at room temperature and 77 K. In the presence of BGP, the spectra showed superparamagnetic doublets at room temperature and the sextet at 77 K, due to the presence of fine particles of iron containing component. Mössbauer studies of hydration products confirmed the formation of nanosize hydration products containing Fe^3?+?. The isomer shift (δ) and the quadrupole splitting (ΔE _Q) values of C₄AF in the cement confirmed iron in an octahedral and tetrahedral environment with +3 oxidation state. The high value of quadrupole splitting showed the high asymmetry of the electron environment around the iron atom. The overall mechanism of the hydration of cement in presence of BGP is discussed.     

Mössbauer study of spin-glass Fe x Zn1−x F2 system

⁵⁷Fe Mössbauer effect measurements in the diluted Ising antiferromagnet Fe _x Zn_1?x F₂ withx=0.25 andx=0.57 at temperatures between 4.2 and 55 K, are reported. DC suceptibility measurements show a spin-glass (SG) phase at low temperatures forx≤0.31. Our Mössbauer spectra show a phase transition to a SG state with antiferromagnetic order (AFSG) forx=0.25 and only antiferromagnetic order forx=0.57.     

Nuclear moment of the 23.8 keV state and hyperfine anomaly in119Sn

Using the Mössbauer effect of the 23.8 keV transition in¹¹⁹Sn, the nuclear magnetic dipole moment of the 23.8 keV 3/2⁺ state is measured to be 0.632(3)μ _n . From a comparison with previously published results a hyperfine anomaly of ?8.8(5)% is obtained.     

Calibration of the isomer shift of119Sn from internal conversion measurement

Radioactive¹¹⁹Sb was implanted into 6 different host matrices, Y, Β-Sn, Pt, Au, Pb and CaSnO₃, and internal-conversion and Mössbauer spectra were measured for the same samples. The isomer-shift calibration constant of the Mössbauer transition of¹¹⁹Sn was derived as δR/R=(0.87±0.25)×10^?4 for R=1.2×A^1/3 fm or, δ〈r²〉=(3.6±1.0)×10^?3 fm².     

Mössbauer studies of Jarosite, Mikasaite and Yavapaiite, and implication to their Martian counterparts

In order to confirm Mössbauer spectra of Jarosite, unidentified Fe³⁺ species (Fe3D3) and Fe₂O₃ found on Martian surface, some Jarosite specimens produced on Earth were characterized by ⁵⁷Fe Mössbauer spectroscopy. For comparison, anhydrous ferric sulfate minerals, Mikasaite (Fe³⁺ _1.56Al_0.44)(SO₄)₃, and Yavapaiite, KFe (SO₄)₂ were also measured. The thermal decomposition products of Jarosite and their hydration products were also traced by scattering Mössbauer spectra (CEMS and XMS). These data are useful for the identification of hydrous and anhydrous ferric sulfate phases on Mars, including Fe3D3.     

Lamb–Mössbauer factor of electronically excited molecular states measured by time‐differential Mössbauer emission spectroscopy

The Lamb-Mössbauer Factor (LMF) of molecular crystals is expected to depend on the electronic molecular states by their different intramolecular vibrational frequencies. Revisiting Mössbauer spectra obtained by time differential Mössbauer emission spectroscopy of the low spin compound [⁵⁷Co/Mn(bipy)₃](PF₆)₂ (bipy= 2,2'-bipyridine) a ratio of 1.25 for the LMFs of the low spin ground state and of an excited high spin state decaying in the Mössbauer time window could be evaluated. The difference found is in line with the change of LMF observed for spin crossover compounds where the excited high spin state is populated by the so‐called LIESST effect. The initial population of the high spin state is close to 100%.     

Spin-transition in nearly cubic site in [FeII(L)3][PF6]2

The spin-transition (¹A₁?⁵T₂) behaviour of a new mononuclear iron(II) compound [Fe^II(L)₃][PF₆]₂[L = 2-[3-(2′-pyridyl)pyrazole-1-ylmethyl]pyridine] has been investigated by ⁵⁷Fe Mössbauer spectroscopy. Analysis of the Mössbauer spectra revealed low value of the quadrupole splitting of the high-spin state which reflects iron(II) to be in nearly cubic lattice site. Mössbauer spectra under light show the light-induced excited spin state trapping effect and the observed quadrupole splitting of the metastable high-spin state is found little sensitive to the high-spin fraction value. DFT calculations are in progress to document the almost cubic nature of the ligand-field acting on the iron atom.     

Formation of Fe i –B pairs in silicon at high temperatures

We report on the detection of Fe _i –B pairs in heavily B doped silicon using ⁵⁷Fe emission Mössbauer spectroscopy following implantation of radioactive ⁵⁷Mn⁺ parent ions (T _1/2?=?1.5 min) at elevated temperatures >?850 K. The Fe _i –B pairs are formed upon the dissociation of Fe _i –V pairs during the lifetime of the Mössbauer state (T _1/2?=?100 ns). The resulting free interstitial Fe_i diffuses over sufficiently large distances during the lifetime of the Mössbauer state to encounter a substitutional B impurity atom, forming Fe _i –B pairs, which are stable up to ～1,050 K on that time scale.     

57Fe and 151Eu Mössbauer studies of magnetoresistive Europium based cobalt perovskites

Eu_0.8Sr_0.2Fe _x Co_1?x O_3?z CMR perovskites with different iron concentrations (x?=?0, 0.025, 0.075, 0.15, 0.3) were investigated by X-ray diffraction, AC magnetic susceptibility, magnetotransport, as well as ⁵⁷Fe and ¹⁵¹Eu Mössbauer spectrometry. The valence state of europium ions was found to be trivalent, independently of the iron concentration. ⁵⁷Fe Mössbauer spectra and magnetic susceptibility of the investigated perovskites presented complementary results for the magnetic transitions.     

Electronic and magnetic properties of the iron borate Fe2BO4

Polycrystalline Fe₂BO₄ was prepared by solid state reactions and its electronic and magnetic properties were investigated by Mössbauer spectroscopy and magnetization measurements. The Mössbauer spectra of Fe₂BO₄ below 270 K indicate the presence of Fe²⁺ and Fe³⁺ sites in the structure, in a ratio 1 : 1. Above this temperature electron delocalization sets in between the divalent and trivalent iron ions and Fe^2.5+ states are observed. The temperature dependence of the Mössbauer spectra and magnetization measurements clearly show the onset of magnetic order below 155 K.     

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.     

A Mössbauer effect investigation of the magnetic behaviour of (Fe,Co)S1 + x solid solutions

The Mössbauer spectra of (Fe, Co)S_{1 + x} were recorded at room temperature and 4.2 K for samples of varying composition to study the magnetic behaviour of the solid solutions. The Mössbauer spectra are split magnetically at iron concentrations above 16% Fe. For samples with less than 16%Fe, the Mössbauer spectra show no evidence of magnetic splitting down to 4.2 K. The room temperature centre shift data appear to vary continuously with composition and the hyperfine magnetic field decreases with decreasing Fe²⁺ concentration. A Mössbauer spectrum of ⁵⁷Fe:CoS at 4.2 K in an external field of 25 kOe showed no evidence of magnetic splitting beyond that caused by the applied field, indicating a net zero internal field.A high spin to low spin transition in Fe²⁺ is ruled out as being responsible for the observed magnetic behaviour on the basis of the centre shift data. The Mössbauer data are interpreted to indicate a substantial increase in electron delocalization towards the ligands as the 〈M-S〉 distance decreases with decreasing Fe²⁺concentration. This causes a reduction in the magnitude of the internal magnetic field contributions as well as a decrease of shielding of the nucleus, giving rise to the observed Mössbauer parameters.The Mössbauer spectrum of ⁵⁷Fe:CoS at room temperature is compared with the spectrum of FeS above the 6.7 GPa phase transition at room temperature. The similarities of the centre shift and the 〈M-S〉 distance in the two phases indicate that covalency may also be responsible for the observed high pressure behaviour of FeS, and not the presence of Fe³⁺ as was originally suggested.     

Spin conversion detected by Mössbauer spectroscopy and μSR on a 1D FeII paramagnetic chain

While magnetic properties of the 1D chain [Fe(hyetrz)₃](4-bromophenylsulfonate)₂ investigated over the temperature range from 300 K to 2 K show paramagnetic behavior, detailed ⁵⁷Fe Mössbauer and muon spin relaxation measurements reveal an unexpected spin conversion. Approximately ~14 % of the high-spin ions are found to convert to the low-spin state with a transition temperature T _1/2?~?120 K.     

Magnetic and Mössbauer characterization of the magnetic properties of single-crystalline sub-micron sized Bi2Fe4O9 cubes

Magnetic and Mössbauer characterization of single crystalline, sub-micron sized Bi₂Fe₄O₉ cubes has been performed using SQUID magnetometry and transmission Mössbauer spectroscopy in the temperature range of 4.2 K ≤ T ≤ 300 K. A broad magnetic phase transition from the paramagnetic to the anti-ferromagnetic state is observed below 250 K, with the Mössbauer spectra exhibiting a superposition of magnetic, collapsed and quadrupolar spectra in the transition region of 200 K < T < 245 K. Room temperature Mössbauer spectra obtained in transmission geometry are identical to those recorded in back-scattering geometry via conversion electron Mössbauer spectroscopy, indicating the absence of strain at the surface. A small hysteresis loop is observed in SQUID measurements at 5 K, attributable to the presence of weak-ferromagnetism arising from the canting of Fe³⁺ ion sublattices in the antiferromagnetic matrix.     

Observation and analysis of a glass transition in amorphous frozen solutions of iron-II chloride

This paper deals with Mössbauer investigations, X-ray diffraction studies and differential calorimetric measurements of the amorphous state of frozen solutions of FeCl₂ in water. This glassy state persists from at least ?180 °C until ?90 °C. All three experimental methods reveal the existence of a glass transition at ?110 °C from an amorphous state to a supercooled liquid. It is shown that for such transitions important conclusions can be drawn from a comparison between the Mössbauer and X-ray diffraction Debye-Waller factor respectively by determining the transmitted Mössbauer intensity far off resonance. Out of the analysis we conclude that the glassy state of quenched ice is due to the hexaquo complexes as implanted impurities which prevail their surrounding from a regular crystallisation. These impurities are also responsible for the glass transition into a supercooled liquid state by releasing new degrees of freedom as e.g. hindered rotational modes.     

Temperature investigations of the spatial spin-modulated structure of multiferroic BiFeO<Subscript>3</Subscript> by means of Mössbauer spectroscopy

The results from ⁵⁷Fe Mössbauer spectroscopic studies of multiferroic BiFeO₃ in a range of tem-peratures including that of the magnetic phase transition are presented. The Mössbauer spectra are processed and analyzed by reconstructing the hyperfine magnetic field distributions and interpreting the spectra with a cycloid-type spatial spin-modulated structure model. The temperature dependences of the hyperfine spectrum parameters (the Mössbauer line shift, the quadrupole shift, and the isotropic and anisotropic contributions to the hyperfine magnetic field) are obtained, along with the anharmonicity parameter of an incommensurate spin wave.     

Mössbauer studies on ultraporous Fe-Oxide/SiO2 aerogel

Magnetic aerogels with very low volume density of ～0.2 g/cm³ were prepared by sol-gel method and supercritical drying. The resulting materials were monolithic and displayed high surface area. By X-ray diffraction and Mössbauer spectroscopy the crystalline phase formed inside the mesopores of the SiO₂ matrix was identified as a spinel iron oxide. Comparison of the magnetic measurements with Mössbauer spectra at various temperatures contributed to the elucidation of the magnetic state of this nanocomposite system with restricted magnetic interactions, in particular its transition to a superparamagnetic state.