The charge states of iron in insulators implanted with57Co and57Fe

Single crystals of α-Al₂O₃ and LiNbO₃ were implanted with⁵⁷Co (dose: up to 2×10¹⁵ atoms/cm²) and with⁵⁷Fe (dose: 2×10¹⁵ atoms/cm²) ions. The Mössbauer spectra revealed the disordered atomic environment. Fe²⁺ and Fe³⁺ charge states were observed. The spectra were compared to the spectra of crystals doped with⁵⁷Co. It was remarkable that in the doped α-Al₂O₃ Fe³⁺ states with slow spin-spin relaxation have appeared. The CEMS study of the samples implanted with⁵⁷Fe resulted in Fe²⁺ ionic states indicating that a fraction of Co atoms can also be in Co²⁺ state.     

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.     

Untersuchung von57Co mit der Reaktion57Fe(p,n)57Co

A neutron time-of-flight investigation of the⁵⁷Fe(p, n)⁵⁷Co reaction performed at bombarding energies of 4.9, 5.6 and 6.2 MeV results in new energy levels of⁵⁷Co. In addition, gamma spectra andn-γ-coincidence spectra were taken to complete the decay scheme of⁵⁷Co up to an excitation energy of 4 MeV.     

Performance-comparison of57Fe DCEMS and UHV-ICEMS

In UHV-applications of DCEMS or ICEMS the optimization of the experimental performance is of utmost importance. For the characterization of the “statistical quality” of the Mössbauer-effect experiment, the statistical utility rateu is defined. The measuring time gain valuesG are determined by comparing values ofu. It is shown with⁵⁷Fe DCEMS and UHV ICEMS measurements performed on various⁵⁷Fe samples applying a channeltron and an extremely low-noise scintillation e^?-counter as electron detector that preferable experimental conditions for ICEMS and DCEMS measurements are different.     

Trends in Mössbauer emission spectroscopy of57Co/57Fe

⁵⁷Co Mössbauer emission spectroscopy is briefly reviewed summarizing mainly the results of the last three to four years. Special emphasis is given to topics easily accessible to groups just starting their activity in this field. On the basis of the trends, the most interesting topics of the upcoming years are estimated.     

In-beam Mössbauer study of 57Fe using a secondary 57Mn beam and ion implantation

We have succeeded in obtaining well-resolved M?ssbauer spectra of ⁵⁷Fe arising from short-lived ⁵⁷Mn ( T _1/2 = 1.45 min) in Si and KMnO₄. The M?ssbauer spectra of ⁵⁷Fe in Si are well fitted with a curve consisting of two singlet lines, one being assigned as the interstitial Fe atoms and the other as substitutional ones. The relative intensities of the two lines infer that 60% of ⁵⁷Fe ( ←⁵⁷Mn) atoms land at the interstitial sites and 40% at the substitutional sites at temperatures between 30 K and 296 K. The result for the KMnO₄ sample suggests a presence of an exotic chemical species corresponding to a higher valence state than Fe^{6 +}. Received: 1 May 2001 / Accepted: 4 December 2001     

Nuclear orientation of57Co

⁵⁷Co has been oriented in an iron foil at temperatures down to 12.7 m^oK. The⁵⁷Co magnetic moment was measured by taking temperature-dependent⁵⁷Co and⁶⁰Co data, and the result was μ(⁵⁷Co)=4.733±0.023 n.m. The mixing ratios, δ=E2/M1, of the intense 122 keV γ-ray as well as of the weak⁵⁷Fe γ-rays, resulting from the decay of the 707 keV level, were measured. We obtained δ (122)=0.1195±0.0010, ?0.186<δ (230) <0.072 or ?6.99<δ (230)相似文献   

Beta decay of57Ni

The decay of⁵⁷Ni was studied using both single and coincidence gamma-ray spectroscopy. Four new low-intensity transitions were observed in the single spectra. The energies and intensities of these transitions related to the 1378 keV transition were determined as 304.1 keV, 0.002%; 696.0 keV, 0.001%, 1350.5 keV, 0.002% and 1603.3 keV, 0.005%. Weak transitions at 541.9, 755.3 and 1279.9 keV were confirmed in agreement to earlier works, and their intensities related to 1378 keV were determined as 0.005%, 0.007% and 0.0012%, respectively.     

Magnetic moment of 57Ni

An extra neutron added to a doubly magic nuclear core should give a nuclear magnetic moment, μ, in close agreement with the Schmidt value. However, the magnetic moment of ⁵⁷Ni, measured through nuclear alignment at 3–20 mK, is equal to ∣μ∣ = 0.88±0.06 μ_N which is only 45% of the Schmidt value. Comparison with several nuclear structure calculations is made.     

Mössbauer study of 57Fe in CVD diamond following 57Mn implantation

⁵⁷Fe Mössbauer spectroscopy, following the implantation of radioactive parent ⁵⁷Mn^?+? ions, has been performed on two chemical vapour deposited diamond samples, one synthesized in 2003 (CVD03) and the other in 2005 (CVD05). The spectra of sample CVD05 were as observed previously in natural IIa diamonds: single lines corresponding to substitutional and interstitial Fe were superimposed on a broad quadrupole split doublet. The site fraction of Fe_i reached 30% at 900 K. The spectra of the CVD03 sample showed, in addition to the above features, a strong contribution (>30%) from a quadrupole doublet attributable to the presence of intrinsic amorphous inclusions in the crystallites. This observation has been confirmed by X-ray diffraction.     

57Co doped oxides as57Fe Mössbauer single line sources

The preparation of several⁵⁷Fe Mössbauer single line sources is reported. It is also discussed the mechanisms involved in the appearance of anomalous charge states for the⁵⁷Fe daughter. The⁵⁷CoO:Li, MgO:⁵⁷Co and Ti⁵⁷CoO₃ appear to be very good candidates to be used as strong sources.     

Mössbauer study of Fe57 and Co57 in Co1 + xV2−xO4

Mössbauer sources and absorbers, prepared by doping Fe⁵⁷ and radioactive Co⁵⁷ into samples of Co_1?xV_2?xO₄ (0 ? x ? 1), were studied in the temperature range of 80–500 K. The source and absorber spectra are very similar. The absence of any Fe²⁺ at the A site can be understood by partial covalent bond formation with an anion. However, the predominance of Fe³⁺ at the B site (with some Fe²⁺ for x = 1) cannot be explained by simple crystal-field or molecular-orbital theories. The x dependence of the isomer shift and of the Fe³⁺B-site quadrupole interaction can be related to changes in the lattice constant and the oxygen parameter. The temperature dependence of the Fe²⁺B-site quadrupole interaction can be fitted in the motional-averaging model. In the range of 0 ? x ? 0.5 the temperature dependence of the isomer shift shows effects of chemical bonding beyond the second-order Doppler shift.     

Implantation of Coulomb excited57Fe

The method of in-beam Mössbauer spectroscopy after recoil implantation of Coulomb excited nuclei is discussed and new setups are described. Particular aspects of time differential measurements are considered. Results obtained by implantation studies of Fe into Si and Al₂O₃ are presented. In silicon the long range diffusion of interstitially implanted iron atoms has been observed between 500 K and 650 K via diffusional linebroadening. The time differential spectra of Si and of Al₂O₃ do not show significant dynamic effects.     

Structure and thermal evolution of57Fe implanted chromium

⁵⁷Fe ion implanted chromium foils have been analyzed by conversion electron Mössbauer spectroscopy. After annealing at temperatures up to 600 °C, the CEM spectra show two magnetic components which are attributed to iron atoms in the core and the outer layer of grains. By means of a simple model using the spectral data, the final average iron grain has been evaluated to be about 5 nm.     

Silicon and transition metal-silicides implanted with57Fe

Si(111) single crystals were implanted with⁵⁷Fe in a broad dose range in order to overlap the concentration range of bulk amorphous Fe _x Si_1−x samples. At high (≥10¹⁶ atoms/cm²) doses the measured hyperfine interaction values were found to be the same as in the bulk amorphous samples, suggesting the same Fe−Si bonding and a very similar structure for the two amorphous phases produced by different methods. A comparison of the isomer shift (δ) and quadrupole splitting (ΔE) values with the values of the stoichiometric crystalliine phases showed the same δ but different δE values indicating similar Fe−Si bonding but different atomic arrangement around the iron atom.     

Non-equilibrium population and slow relaxation of Fe2+ in57Co:LiNbO3 and57Co:LiTaO3 single crystals

The Fe²⁺ fraction observed in the Mössbauer emission spectra of⁵⁷Co:LiNbO₃ and⁵⁷Co:LiTaO₃ exhibits both slow electronic relaxation and nonthermal populations of them _s sublevels of the⁵A_lg orbital singlet ground state at low temperatures (T<15 K) in high magnetic fields. The relaxation rates depend on temperature and on the angle ? between the magnetic field and the crystallographicc-axis.