Combined Mössbauer and LIII-edge X-ray absorption study of mixed- valent EuPd2Si2 and EuNi2P2

The mean valence of Eu is determined by L_III-edge X-ray absorption (L_III-XA) and ¹⁵¹Eu Mössbauer isomer shift measurementd for the mixed-valent compounds EuPd₂Si₂ and EuNi₂P₂ in the temperature range from 1.7 to 300 K. For EuPd₂Si₂, the behaviour of the satellite line observed in the Mössbauer spectra was investigated in detail. From a comparison of the L_III-Xa and Mössbauer results obtained on identical samples the valence/isomer shift calibration problem as well as possible final-state effects in L_III-XA spectra are discussed.     

Hydrogen absorption in LaNi4.9Fe0.1

The magnetic properties of LaNi_4.9Fe_0.1 and its hydride have been studied by making Mössbauer and magnetic susceptibility measurements. ⁵⁷Fe Mössbauer spectroscopy shows a small increase in the isomer shift after hydriding. An increase in the magnetic susceptibility after hydriding was observed.     

Mössbauer effect on YFe3 compound

The thermal variation of the Mössbauer parameters of the YFe₃ compound between 78 K and T_c is studied. The results agrees well with the magnetic measurements. For the iron site 18 (h) the presence of an anisotropic interaction splits the Mössbauer spectrum into two six-lines patterns with the intensities in 2:1 ratio but above 400 K the intensities of the Mössbauer spectra of the sublattices are in 1 : 2: 6 ratio in agreement with crystallographic data.     

Studies of thermal decomposition of (NH4)2Fe(SO4)2·6H2O

Thermal decomposition products of the Mohr salt (NH₄)₂Fe(SO₄)₂·6H₂O have been studied and identified using the Mössbauer effect, X-ray diffraction, infrared spectroscopy, and the gravimetric and thermal differential methods. It has been found that the Mohr salt heated for 96 hr. in air at 520K changes to a single substance identified as NH₄Fe(SO₄)₂ with a single Mössbauer line (width 0.30 mm/sec; isomeric shift 0.30 mm/sec). When the Mohr salt is heated for 1 hr. in air at 770 K it changes to Fe₂(SO₄)₃ with a single Mössbauer line (width 0.33 mm/sec; isomeric shift 0.31 mm/sec) strikingly similar to line of NH₄Fe(SO₄)₂.     

On the iron valence states in B2O3-PbO-GeO2 glasses

The Mössbauer effect measurements performed on 20Fe₂O₃ 80 3B₂O₃ (1?x)PbO xGeO₂ glasses show that the ratio between the number of ferrous ions to the total number of iron ions decreases by increasing the GeO₂ content. The Curie constants calculated from the distribution of iron cations obtained by Mössbauer effect data are in agreement with the values determined from magnetic measurements. Finally, we discuss the influence of the glass composition and melting temperature on the iron valence states.     

On the hyperfine field of γ-Fe2O3 small particles

The smaller magnetic hyperfine field of γ-Fe₂O₃ small particles below the superparamagnetic blocking temperature compared to that found in larger crystals is discussed in terms of surface and of intrinsic size effects by using Mössbauer spectroscopy.     

A Mössbauer and X-ray investigation of ξ-Fe2N

Mössbauer spectra of ξ-Fe₂N at 4·2°K, 78°K and room temperature are presented. The Mössbauer parameters are compatible with the nitrogen donor model previously found to be applicable to the lower iron nitrides. X-ray analyses of this phase confirm the structure previously reported. Mössbauer and X-ray spectra for partially nitrided iron foils containing γ′, ε and ξ iron nitrides are also discussed.     

The coordination of Co2+ions in Co substituted magnetites,Fe3−xCoxO4, with x⩽0.04

⁵⁷Fe Mössbauer spectra at room temperature, both with and without external magnetic field, indicate that Co²⁺ ions in Co_xFe_3?xO₄spinels (x?0.04) are situated on the octahedral B sites. The Mössbauer parameters are listed and the existence of unpaired Fe³⁺ ions is evidenced.     

Mössbauer study of the magnetic axis in RbFeF3 in the interval T2<T<TN

The antiferromagnetic axis in RbFeF₃ in the interval T₂<T<T_N has been expected to be along [111] from powder Mössbauer studies and along [001] from an X-ray diffraction study. We report our direct observation of the magnetic axis by Mössbauer spectroscopy using stressed single crystal samples. The results show that the magnetic axis is along [111].     

Magnetic Study of Nanocrystalline Ferrites and the Effect of Swift Heavy Ion Irradiation

100 MeV Si⁺⁷ irradiation induced modifications in the structural and magnetic properties of Mg_0.95Mn_0.05Fe₂O₄ nanoparticles have been studied by using X-ray diffraction, Mössbauer spectroscopy and a SQUID magnetometer. The X-ray diffraction patterns indicate the presence of single-phase cubic spinel structure of the samples. The particle size was estimated from the broadened (311) X-ray diffraction peak using the well-known Scherrer equation. The milling process reduced the average particle size to the nanometer range. After irradiation a slight increase in the particle size was observed. With the room temperature Mössbauer spectroscopy, superparamagnetic relaxation effects were observed in the pristine as well as in the irradiated samples. No appreciable changes were observed in the room temperature Mössbauer spectra after ion irradiation. Mössbauer spectroscopy performed on a 12 h milled pristine sample (6 nm) confirmed the transition to a magnetically ordered state for temperatures less than 140 K. All the samples showed well-defined magnetic ordering at 5 K, whereas, at room temperature they were in a superparamagnetic state. From the magnetization studies performed on the irradiated samples, it was concluded that the saturation magnetization was enhanced. This was explained on the basis of SHI irradiation induced modifications in surface states of the nanoparticles.     

First order magnetic phase transition in tetragonal NpCu2Si2

Magnetization and Np²³⁷ Mössbauer studies of the tetragonal compounds NpM₂Si₂ (M = Cr, Mn, Fe, Co, Ni, Cu) were performed. NpMn₂Si₂ is ferromagnetic. All other compounds order antiferromagnetically. Only in NpCu₂Si₂ the Mössbauer studies reveal a first order magnetic phase transition at T_N = 34 K. It is interpreted in terms of Blume's model, originally developed for cubic UO₂.     

Surface characterization and catalytic CO + H2 reaction on Fe82.2B17.8 amorphous alloy

Fe_82.2B_17.8 amorphous ribbon has been used as a catalyst for the Fischer-Tropsch-type reaction of CO+H₂. Specific activity has been found to be at least an order of magnitude higher than that of either the crystallized ribbon of identical composition or the supported iron catalyst. Before and after the catalytic tests the ribbons were characterized by XRD, XPS, UPS and Mössbauer spectroscopy in transmission and in conversion electron modes. Conversion electron Mössbauer spectroscopy and UPS proved that the surface of the amorphous ribbons is being partially crystallized during 8000 min reaction time at a maximum reaction temperature of 560 K. The superior catalytic activity has been explained by stabilization of the small iron particles and Fe₂O₃ by boron atoms at the surface and by suppressed carbide formation.     

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 properties and spin order of Sr7Fe10O22

The magnetic properties of Sr₇Fe₁₀O₂₂ have been investigated by means of magnetic susceptibility and Mössbauer absorption measurements. This compound proved to be antiferromagnetic with a Néel temperature T_N = 425 K; the magnetic susceptibility is constant from the lowest measuring temperature (78 K) up to T_N.The Mössbauer measurements and the analogies with “brownmillerite” type compounds indicate that iron ions occupy one octahedral and two tetrahedral different sites. An antiferromagnetic spin configuration with moments lying in the ab plane appears to be consistent with the experimental results. A small spontaneous magnetic moment was observed at room temperature with features resembling those of strontium hexaferrite; a weak ferromagnetic behavior can not however be excluded taking into account the aforementioned susceptibility behaviour.     

Mössbauer spectroscopy of magnetic phases in FeCl2 · 2H2O

Mössbauer spectroscopy of the three magnetic phases of single crystal FeCl₂ · 2H₂ in external magnetic fields at 4.2 K is reported.     

Investigation of a superparamagnetic phase in BiFeO8 by means of Mössbauer effect

A superparamagnetic phase in BiFeO₃ was found by means of the Mössbauer effect. This phase appears at room temperature as a doublet superimposed upon the normal BiFeO₃ six-line Mössbauer spectrum. The superparamagnetic doublet is believed to belong to small α-Fe₂O₃ particles which are superparamagnetic at room temperature. The appearance of a superparamagnetic phase may explain the weak ferromagnetism observed in BiFeO₃ in several reports.     

Interactions magnetiques hyperfines pour les atomes d'impurete 121Sb5+ dans FeF3

The Mössbauer spectra of ¹²¹Sb⁵⁺ in the antiferromagnetic FeF₃ composition indicates the presence of a magnetic transfer region amongst the nucleus of the impurities of the antimony: H_eff(77°K) = 110 ± 15 kOe. The comparison of the value of H_eff observed on the nucleus of ¹¹⁹Sn⁴⁺ and of ¹²¹Sb⁵⁺ in the matrix of FeF₃ suggests a different mechanism of transference of the magnetic hyperfine region in relation to the position of the same pair of Mössbauer isotopes in the midst of the oxygen matrix.     

Linear chain antiferromagnetism in FeOHSO4

Magnetic susceptibility measurements on Fe OH SO₄ suggest linear chain antiferromagnetism up to at least 200°K with a transition to three dimensional antiferromagnetism at 56°K. Mössbauer spectra show magnetic hyperfine splitting up to ～ 90°K and this is interpreted in terms of intrachain spin correlation with relaxation effects caused by interchain spin relaxation. The 4·2°K spectrum is strongly asymmetric because of the admixture of nuclear eigenfunctions by non-parallel magnetic and quadrupolar principal axes systems. Using this the first complete derivation of a complete set of hyperfine interaction parameters from a Mössbauer spectrum is made and correlated with the crystallographic structure.     

The B-site Mössbauer linewidth in Fe3O4

It is found that the linewidth of the B-site Mössbauer spectrum of an Fe₃O₄ single crystal at room temperature is strongly dependent on the direction of the externally applied magnetic field. The broadening of the line 1B observed in polycrystalline materials is concluded to be largely determined by magnetic dipolar and electric quadrupolar effects, and therefore cannot serve as proof for an electron hopping model.     

A Mössbauer investigation of diamagnetic,semiconducting alpha-FeP4

Measurements of the magnetic and electrical properties show the ambient pressure (α) modification of FeP₄ to be diamagnetic and semiconducting. Its ⁵⁷Fe Mössbauer spectra were recorded at room temperature and liquid nitrogen temperature. They are discussed together with the Mössbauer spectra of the other iron phosphides. There is a significant difference between the isomer shifts of the intermetallic-like phosphides with high coordination for all atoms and the polyanionic phosphides with low coordination numbers.