Mössbauer emission study of57Co: YBa2Cu3O7−y HTSC

Mössbauer emission spectroscopy is performed on⁵⁷Co:YBa₂Cu₃O_7–y oxides in a temperature range from 300 K to 77 K. The spectra show, at least two different location for the⁵⁷Co(⁵⁷Fe) impurities. The isomer shift and quadrupole splitting values of the⁵⁷Fe daughter are coincident with those observed in⁵⁷Fe absorption experiments. From the analysis of theIS andQS values as well as from the relative location of Fe impurity levels in the HTSC matrix it is argued that:a) Co impurities enters into the lattice mainly in the Cu1 sites, but some of them have a higher coordination number.b) The daughter⁵⁷Fe exists as localized Fe⁴⁺ state.c) The parent⁵⁷Co enter as a localized Co³⁺ state. These conclusions appear consistent with the observed increase ofN(0) on doping with Fe or Co ions and with the existence of localized magnetic moments as determined from paramagnetic susceptibility measurements.     

Temperature dependence of the anomalous emission line intensities in57Co:LiTaO3-initial population and relaxation

Mössbauer spectra of⁵⁷Co: LiTaO₃ single crystals were recorded in an external longitudinal magnetic field of 6 T at different temperatures between 4.2 K and 150 K. The spectra were taken at two different orientations of the crystallographicc-axis relative to the magnetic field. The line intensities of the Fe³⁺-subspectra show a temperature dependent anomalous population of the three Kramers doublets of the Fe³⁺ spinS=5/2 ground state. A relaxation broadening is observed at higher temperatures, which cannot successfully be reproduced within a relaxation model taking into account only the six lowest lying electronic states.     

Magnetic field and temperature dependence of the anomalous emission line intensities in LiNbO3:57Co-initial population and relaxation

The magnetic field dependence of the anomalous Fe³⁺ emission line intensities in LiNbO₃:⁵⁷Co cannot be due to a direct spin-lattice relaxation process in the⁶S ground state. Raman and Orbach processes in the ground state are ruled out by the temperature independent behaviour of the spectra. The observed line intensities are proportional to the initial populations of the corresponding Zeeman levels.     

New time-differential Mössbauer emission measurements on the high-spin→low-spin relaxation in [57Co/Co(phen)3](ClO4)2

Using our new spectrometer for time-differential Mössbauer emission spectroscopy we reinvestigated the high-spin→low-spin relaxation following the⁵⁷Co(EC)⁵⁷Fe process in [⁵⁷Co/Co(phen)₃](ClO₄)₂ (phen=1,10-phenanthroline). In contrast to former investigations we found a temperature dependent initial population less than 1 for the metastable high-spin states. The results and the data evaluation method are presented.     

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.     

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.     

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.     

Calculation of emission spectra in terms of a stochastic relaxation model: Fe3+ in LiNbO3

Mössbauer emission spectra of LiNbO₃:⁵⁷Co single crystals at 100 K in a magnetic field of 4 T show Fe³⁺ line intensities corresponding to a nearly Boltzmann population of the⁶A_1g Zeeman sublevels. Supposing that this is due to a spin-lattice relaxation in the ground state, no relaxation matrix can reproduce the shape of the spectrum. We conclude that the initial populations are temperature dependent due to spin-lattice relaxation within the \(\Gamma _6 ^T \) excited doublet.     

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.     

Mossbauer spectroscopy on57Co implanted SiO2

Conclusions Different charge states of⁵⁷Fe are identified in the⁵⁷Co implanted SiO₂ matrix.It is interesting to see that the states appearing in solid oxygen [2 ] also appear in the SiO₂ matrix, although in neither of the matrices a preferential interpretation of the S₁-line being Fe^{+ 6} or Fe⁰, can be achieved.Further, implantation of⁵⁷Fe in SiO₂ could reveal whether the states appearing in the⁵⁷Co implanted SiO² are really after decay effects or part of a (⁵⁷Fe-SiO₂)-structure.The authors wish to thank Prof. P. Boolchand for the SiO₂ samples and L. Verwilst for the ion implantation.     

The magnetic moment of the lowest 3/2− state in57Co

The reaction⁵⁴Fe(α, n)⁵⁷Ni has been used to implant⁵⁷Co isotopes in ferromagnetic iron. Theg-factor of the lowest 3/2^? state is determined using the internal field in a constant angle reversed field method. The angular correlation of the 127–1,378 keV cascade is also measured. The result of the angular correlation measurement together with reaction data is consistent withp _3/2 andp _1/2 single particle assignments to the lowest 3/2^? resp. 1/2^? state. In view of this statement the quenching of the magnetic moment is discussed.     

Nuclear larmor precession of the 14 keV state of57Fe in α-iron following the reaction56Fe (d,p)57Fe

The spin precession of the 14 keV state of⁵⁷Fe, excited by the⁵⁶Fe(d,p) reaction was observed in ferromagnetic Fe. The data yield a magnetic field of ? 330±4 kG and a relaxation time τ _r > 500 ns at room temperature.     

57Co emission studies of cupric oxide

Results on the incorporation, valence and spin states of Fe(Co) in CuO (with reference to similar studies on high temperature superconductors) and coupling of the Fe(Co) moment to the Cu magnetism in CuO are presented. Freshly prepared⁵⁷Co: CuO shows two quadrupole doublets D₁ and D₂ withQ.S. of 2.49 and 1.52,I.S. of 0.35 and 0.70 mm/s and relative abundance of 74% and 26%, respectively at room temperature, the abundance being dependent on time in a sample exposed to ambient conditions and reaching 38 to 62% fifteen months after preparation. Below,T _N=225¹K, a typical combined magnetic-quadrupole interaction pattern is observed with a single saturation magnetic hfs of 25.6 T, central shift of 0.82 mm/s and a single |E _Q|=1.62 mm/s at 4.2 K. External magnetic field spectra reveal an antiferromagnetic behaviour of the Fe(Co) ion. Temperature dependence of the magnetic hfs is fitted in the framework of the molecular field approximation allowing different spins and coupling constants for Cu and Fe(Co).     

Non-equilibrum population of the Fe3+ electronic states after the electron capture in57Co: LiTaO3

Mössbauer emission spectra of⁵⁷Co: LiTaO₃ show as a consequence of the nuclear decay anomalous emission line intensities in the subspectra of Fe²⁺ and Fe³⁺. Magnetic field and angle dependence of Fe³⁺ intensities can be explained by taking into account polarization-and crystal-field effects in the excited states. The experimental results for LiTaO₃ are in good agreement with theory and previous measurements on LiNbO₃.     

57Fe Mössbauer study of Li x Fe1-y Co y PO4 (y = 0, 0.1, 0.2) as cathode material for Li-ion batteries

Lithium iron phosphates LiFe_1-y Co _y PO₄ (y = 0, 0.1, 0.2) exposed to a charging process were studied by ⁵⁷Fe Mössbauer spectroscopy taking into account XRD and SEM data. Hyperfine parameters of the spectra were determined above and below the magnetic ordering temperature for all the samples. It was shown that the presence of Co impurity atoms in lithium phosphates gives no effect on the hyperfine interaction of ⁵⁷Fe²⁺ cations. However, Co atoms in the nearest cation environment of Fe atoms lead to a significant change of the hyperfine interactions of ⁵⁷Fe³⁺ cations. The Co impurity atoms distribution over the positions of the iron atoms in the structure is found not to be statistical,but correlated.     

Evaluation of the Fe2+/Fe3+ ratio from57Co Mössbauer emission spectra: Influence of the relaxation of Fe3+

The Fe³⁺ fraction after the EC of⁵⁷Co is usually evaluated supposing that ferric ions contribute a quadrupole doublet to Mössbauer emission spectra. It is shown that a not sufficiently fast relaxation of the electron spins may falsify the evaluated intensity even by a factor 2. Additional information can be gained from measurements performed in a large velocity span at low temperatures in high magnetic fields.     

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.     

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   

Emission Mössbauer studies of 57Co2+ and 119Sb5+ adsorbed on γ-Fe2O3 and NiFe2O4 surfaces

Summary Surface chemical states of⁵⁷Co²⁺ and¹¹⁹Sb⁵⁺ ions adsorbed on γ-Fe₂O₃ and NiFe₂O₄ were studied in the presence of the aqueous phase using the magnetic interaction between the substrates and⁵⁷Fe²⁺ or¹¹⁹Sn⁴⁺ arising from the adsorbed species. Two chemical forms were observed for the⁵⁷Co²⁺ adsorbed on γ-Fe₂O₃; one giving a peak in the high-field region and another giving a broad distribution in the lower fields, which were attributed to⁵⁷Co²⁺ at surfaceB sites of the spinel structure of γ-Fe₂O₃ and⁵⁷Co²⁺ species weakly bonded to the substrate, respectively. In case of the NiFe₂O₄ substrate, the latter species was dominant and was converted to the former by heating. Most of the¹¹⁹Sb⁵⁺ ions adsorbed on the γ-Fe₂O₃ and NiFe₂O₄ particles were found to have a certain magnetic interaction with the magnetically ordered ions of the substrates. Paper presented at the ICAME-95, Rimini, 10–16, September 1995     

Chemical state of cobalt doped in and adsorbed on α-(Fe1-x Cr x )2O3 by emission Mössbauer spectroscopy

Mössbauer parameters (internal magnetic field, quadrupole splitting and isomer shift) of both α-(Fe_1-x Cr _x )₂O₃ (x=0, 0.2 and ≈1.0) doped and undoped with⁵⁷Co are in good agreement at room temperature and 77 K, except internal magnetic fields of both α-Cr₂O₃ doped with⁵⁷Co and enriched⁵⁷Fe. It is thus concluded that⁵⁷Fe produced from⁵⁷Co occupies the octahedral sites as Fe³⁺ with small distortion from cubic symmetry. Different internal magnetic field of doped α-Cr₂O₃ may be explained by the difference of canting of the spin against the [111] axis. By adding zinc ions, the adsorption of Co²⁺ ions on α-Fe₂O₃ particles in aqueous solution is decreased considerably in the pH range of 6.5–9.5 at 303 K, but the internal magnetic field of⁵⁷Co adsorbed on α-Fe₂O₃ does not change, although the internal magnetic fields of both samples with and without zinc ions are smaller than that of bulk α-Fe₂O₃ doped with⁵⁷Co. This suggests that densities of⁵⁷Co ions on the surface of α-Fe₂O₃ may be decreased by the addition of zinc ions and⁵⁷Co ions adsorbed on α-Fe₂O₃ are weakly bound on the substrate.