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.     

Mössbauer studies of Dy2Fe17−yAly hydrides

The x-ray and Mössbauer measurements of both⁵⁷Fe and¹⁶¹Dy in Dy₂Fe_17–y Al (y=0, 1,5 and 3) compounds and their hydrides are reported.Hydrogenation slightly increases the lattice parameters. An appreciable increase of the isomer shift and the hyperfine field at⁵⁷Fe nuclei is observed after hydrogenation. The hyperfine field for both the parent compound and its hydride decreases with increasing Al content across the series. Only a small variation of the hyperfine field at¹⁶¹Dy nuclei is noticeable after hydrogenation.     

Hyperfine field interactions in crystalline Fe3, P1−xBx alloys

Mössbauer and NMR studies of hyperfine interactions in crystalline Fe₃P_1–XB_X compositional series, aiming toward a better understanding of the nature of direct (HF) and transferred hyperfine fields (THF) at the⁵⁷Fe and¹¹B sites are presented.     

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.     

Effects of nitrogen and vanadium on the57Fe hyperfine field of RFe12−x V x N y (R=Y,Nd)

Magnetization and⁵⁷Fe Mössbauer measurements were carried out on RFe_12–x V _x N _y compounds (R=Y and Nd,x=1.7 and 2.2) and the effects of nitrogen and vanadium atoms on the⁵⁷Fe hyperfine fields at the different iron crystallographic sites were investigated. The hyperfine field decreases with increasing number of vanadium neighbour atoms at all the iron sites. The hyperfine field is strongly enhanced in the nitrogen composition withy>1 where the compound tends to transform into an amorphous-like solid. The iron moment deduced from the hyperfine field increases more upon nitrogenation for the 8i-site than for the other sites, and exceeds the moment of bcc iron.     

Hyperfine magnetic fields in Fe−Co alloys and their tempera ture dependences

We obtained⁵⁷Fe hyperfine field parameters from Fe₁−x-Co _x alloys (0≤x≤0.6) from 77 K to 900 K. We first discuss the origin of the low temperature hyperfine fields in terms of the 3d and 4s electrons at⁵⁷Fe atoms. The⁵⁷Fe hyperfine magnetic field (hmf) of Fe-Co alloys depends more weakly on temperature than the hmf of pure Fe. This temperature dependence occurs because the alignment of the magnetic moments at both the Fe atoms and at the Co atoms depend on temperature in the same way as the bulk magnetization of Fe-Co alloys.     

Mössbauer effect study of the magnetic state of iron atoms in Fe-Ni 36 wt.% Invar alloys

The⁵⁷Fe Mössbauer spectra of the Fe-Ni 36 wt.% Invar alloy at different temperatures (300–530 K) have been measured. The experimental results indicate that the hyperfine field distributions are characterized by dual peaks. The temperature dependence of the hyperfine field indicates that some iron atoms may transfer from the ferromagnetic state to the antiferromagnetic one with increasing temperature, and that the variation of the ratio of numberN ₀ of the iron atoms in the antiferromagnetic state to the numberN _h in the ferromagnetic state with temperature will obey the thermodynamic relationship.     

Single-Crystal Fe Q-Band ENDOR Study of the 4 Iron–4 Sulfur Cluster in its Reduced [4Fe–4S] State

⁵⁷Fe Q-band ENDOR has been used to study the [4Fe–4S]¹⁺ state created by γ irradiation of single crystals of the synthetic model compound [N(C₂H₅)₄]₂[Fe₄S₄(SCH₂C₆H₅)₄] enriched in ⁵⁷Fe. This compound is an excellent biomimetic model of the active sites of many 4 iron–4 sulfur proteins, enabling detailed and systematic studies of its oxidized [4Fe–4S]³⁺ and reduced [4Fe–4S]¹⁺ paramagnetic states. Taking advantage of the fact that Q-band ENDOR, in contrast with X-Band ENDOR, allows for a very good separation of the ⁵⁷Fe transitions from those of the protons, the complete hyperfine tensors of the four iron atoms for the [4Fe–4S]¹⁺ species has been measured with precision. For each iron atom, the electron orbital and electron spin isotropic contributions have been determined separately. Moreover, it is remarkable that two ⁵⁷Fe hyperfine tensors attributed to the ferrous pair of iron atoms are very different. In effect, one tensor presents a much larger anisotropic part and a much smaller isotropic part than those of the other. This difference has been interpreted in terms of a differential electron orbital hyperfine interaction among the two ferrous ions.     

Novel ternary iron-rich,rare-earth iron silicides: R3(Fe1−x Si x )22 (x ∼ 0.16)

In our search for new ternary rare-earth (R) iron silicon intermetallic compounds, a novel ternary phase with the chemical formula R₃Fe_18.5Si_3.5 has been identified with the RFeSi ratio in the range of 12–1574–7810–12. We have studied compounds with R=Gd, Tb, Dy, Ho, Er, Tm and Lu. All of the samples, except for R=Lu, form the new ternary phase3–22. X-ray diffraction data suggest that for R=Gd and Tb, the crystal structure is the rhombohedral Th₂Zn₁₇-type structure and for R=Dy, Ho, Er and Tm, the hexagonal Th₂Ni₁₇-type structure. We suggest that a 1/4 replacement of the R sites by Fe(Si) dumbbells in the CaCu₅-type structure leads to the new3–22 phase, which is an ordered version of the TbCu₇-type structure.⁵⁷Fe Mössbauer spectroscopy has been used to determine the hyperfine parameters of the⁵⁷Fe nuclei in the3–22 compounds. At 295 K, the average hyperfine field of the new3–22 phase ranges from 19.8 T (R=Ho) to 22.2 T (R=Gd). Thermogravimetric analysis (TGA) of these compounds gives Curie temperatures in the range 467 K (Tm)–549 K (Gd). Furthermore, our Mössbauer analysis enables us to investigate the preferential site occupancy shown by Si in these structures.     

Hyperfine fields and chemical order in Fe-Ge

Films of Fe_0.79Ge_0.21 were synthesized by ion beam sputtering, and were annealed at temperatures from 150 to 500 °C. The as-prepared materials comprised chemically disordered bcc crystallites, but short-range and long-range D0₃ chemical order developed upon annealing. The⁵⁷Fe hyperfine magnetic field distribution can be understood approximately with a model of magnetic response, so the hyperfine magnetic field distribution can be used to follow the changes in chemical short-range ordering. Large local isomer shifts were observed at⁵⁷Fe atoms near Ge atoms.     

Mössbauer study and magnetic moments of Fe90−xCoxZr10 and Fe90−xNixZr10 amorphous alloys

The⁵⁷Fe Mössbauer spectroscopy of amorphous Fe_90–xCo_xZr₁₀ and Fe_90–xNi_xZr₁₀ provided strong evidence for the unusual large enhancement of the Fe magnetic moment in these alloys.     

Magnetic coupling in Gd(Fe6−x Cr x )Al6: A57Fe Mössbauer study

⁵⁷Fe Mössbauer measurements have been made on the ternary ThMn₁₂-type intermetallic compounds Gd(Fe_6–x Cr _x )Al₆ withx=0, 0.5, 1.0, 1.5 and 2.0, at temperatures of 4.2 and 77 K. The principal effect of the Cr substitution is to reduce the⁵⁷Fe magnetic hyperfine field at 4.2 K in this series. The analysis of the⁵⁷Fe Mössbauer spectra is consistent with a ferromagnetic coupling between the Gd and Cr magnetic moments. These results are in agreement with previous studies by Felner et al. on GdCr₆Al₆, in which a ferromagnetic ordering withT _C=170 K was observed.On leave from Applied Acoustics Institute, Shaanxi Teachers University, Xian, PR China.     

57Fe Mössbauer studies of U(Fe1−x Co x )2

In the pseudo-binary alloy system U(Fe_1–x Co_x)₂, the ordering transition temperature and the magnetic moment decrease rapidly with x.⁵⁷Fe Mössbauer measurements on the alloys (x=0.08 and 0.20) have been performed as a function of temperature. The observed hyperfine field at the⁵⁷Fe nucleus is much reduced with respect to that in UFe₂.     

On the transferred hyperfine interaction in substituted yig

NMR of⁵⁷Fe is studied in a number of (M_xY_3–x) Fe₅O₁₂ garnets for small concentrations of M (M is either trivalent RE ion –Ho 3+, Gd 3+, Nd3+, Pr 3+, La 3+ or Bi 3+ ion). Beside the main resonance lines, the satellites were observed, which correspond to those Fe, in vicinity of which the impurity M is located. After correcting for the dipolar field, the field corresponding to the change of the transferred hyperfine interaction in M³⁺–O^2–-Fe³⁺ vs. Y³⁺–O^2–-Fe³⁺ triad was deduced from the satellites splitting. The analysis of the results indicates that the observed change in the transferred hyperfine field is mainly connected with the transfer of electrons between M³⁺ and Fe³⁺ ions and not with the local deformation around the impurity.     

Investigations of crystal and magnetic properties of Dy-Fe intermetallic compounds

The crystal and magnetic properties of Dy₂Fe₁₇, Dy₆Fe₂₃, DyFe₃ and DyFe₂ intermetallic compounds are investigated with X-ray, magnetometric, ⁵⁷Fe and ¹⁶¹Dy Mössbauer effect methods. The X-ray analysis shows that investigated compounds are single phases with Th₂Ni₁₇, Th₆Mn₂₃, PuNi₃ and NgCu₂ type crystal structures, respectively. The magnetometric measurements prove their ferrimagnetic behaviour, localization of Fe magnetic moments and long range Fe-Fe exchange magnetic interactions. The crystal field effects induce magnetic anisotropy which results in local magnetic symmetry or iron atoms lower than the crystal one. This is observed by the Mössbauer effect method. The values of ¹⁶¹Dy hyperfine magnetic fields measured for investigated compounds exceed that found in metallic dysprosium due to polarization of conduction electrons by 3d-electrons of iron atoms. The weighted average value of ⁵⁷Fe hyperfine magnetic field decreases with the increase of Dy content in the compounds.     

Influence of the local environment on the hyperfine interactions in Zr(Fe1-xCox)2 compounds

Ferromagnetic Laves phase compounds Zr(Fe_1-xCo_x)₂ have been investigated by means of the Mössbauer effect (⁵⁷Fe) and by the time-dependent perturbed angular correlation of \gamma -rays (¹⁸¹Ta) technique. It has been concluded from ME experiments that by exchange of Fe by Co in the nearest neighbour shell of the nuclear probe the hyperfine magnetic field acting on ⁵⁷Fe decreases by 10--12 kG. The analysis of the TDPAC experiments revealed that two different hyperfine magnetic fields: B₁ ^hf(Ta)~ 61 kG and B₂ ^hf(Ta)~ 88 kG act on the ¹⁸¹Ta nuclei. Both have a negative sign.     

Mössbauer spectroscopy on RE2Fe14BHx (RE-Y,Ce, Dy,Er) alloys

RE₂Fe₁₄B alloys and some of their hydrides have been studied through⁵⁷Fe and¹⁶¹Dy Mössbauer spectroscopy (MS). For both the paramagnetic and ordered phases a consistent and physically sound analysis of the⁵⁷Fe spectra is presented. Fe hyperfine fields and the local magnetic moments are obtained and compared with magnetic and structural data. A spin reorientation is observed for Er₂Fe₁₄B. A constant collinear structure down to 4.2 K was determined for the other samples. The¹⁶¹Dy spectra are interpreted for a pure ¦J_Z=15/2 > ground multiplet in Dy₂Fe₁₄B and its hydride. The B₂ crystal field parameters were estimated empirically for the Dy-alloy. Their values can account for the anisotropy in the compounds.     

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.     

A comparison of crystalline and quasicrystalline Al-Mn-Fe compounds

New complex metallic alloys of the Taylor phase Al₃Mn with 8, 10 and 12% Fe substitution are investigated by ⁵⁷Fe M?ssbauer spectroscopy. Two groups of subspectra, with different hyperfine parameters are obtained, and are allocated to Fe sites with only Al nearest neighbors and Fe sites with both Al and Mn in the first shell. No difference between crystalline and quasicrystalline compounds is found indicating that long range periodicity plays a minor role.     

X-ray and Mössbauer study of rapidly solidified Ce20Fe80 ribbons; effect of the quenching rate

Ce₂₀Fe₈₀ ribbons have been produced by planar flow casting under an He atmosphere at linear wheel velocities between 19 and 29 m s^–1. Analysis of ribbons by X-ray diffraction and⁵⁷Fe Mössbauer spectrometry in the temperature range 77–300 K shows that the ribbons are crystallized. For higher velocities, the ribbon is constituted of the two equilibrium phases CeFe₂ and Ce₂Fe₁₇, but, for lower velocities, there appears a third iron metallic phase, which can be explained by the quenching rate of the melt. A coherent hyperfine parameter set was deduced from fitting Mössbauer spectra in the whole temperature range.