Magnetic behaviour and DCEMS study of SnO2 films implanted with 57Fe

Fe implanted SnO₂ films (5 × 10¹⁶ and 1 × 10^{17 57}Fe ions/cm²) characterized by conversion electron Mossbauer spectroscopy (CEMS) are reviewed. The substrate temperatures affect the growth of precipitated iron oxides. The Fe ion implanted film at room temperature (RT) shows no Kerr effect and no magnetic sextet in CEM spectra. The SnO₂ film implanted with ⁵⁷Fe at the substrate temperature of 300 °C show a small Kerr effect although the magnetic sextet is not observed, but post-annealing results in the disappearance of the Kerr effect. This magnetism is considered to be due to defect induced magnetism. Some samples were measured by CEMS at 15 K. SnO₂ (0.1 at %Sb and 3 at %Sb) films, implanted at 500 °C and the post-annealed samples, show RT ferromagnetism due to formation of clusters of magnetite and maghemite, respectively. The layer by layer analysis of these films within 100 nm in thickness has been done by depth sensitive CEMS (DCEMS) using a He + 5 % CH₄ gas counter. The structures and compositions of Fe implanted SnO₂ films, and the effects due to post-annealing were investigated.     

Evidence for fast diffusion of57Fe implanted in cu from depthselective conversion-electron Mössbauer spectroscopy (DCEMS)

The DCEMS technique has been applied to observe drastic changes with time of the ion-implanted⁵⁷Fe concentration profilein a Cu foil. Spectral changes observed at selected electron energies may be related to changes as a function of depth in the⁵⁷Fe local surroundings.     

On the performance of UHV-ICEMS experiments

Integral Conversion Electron Mössbauer Spectroscopy (ICEMS) when aimed at the study of clean surfaces in UHV often leads to unfavourable measuring geometry and consequently to long recording times. Possible means of shortening of the measuring times are analyzed. It is shown that criteria for experimental preferences may be distinctly different for different sample structures and for different kinds of electron detectors. The experimental performance of a channeltron and a low-noise scintillation counter for UHV-ICEMS applications is determined on base of measurements on different samples. It is demonstrated that for such experiments the channeltron provides the higher performance due to the substantial contribution of low energy (50–100 eV) electrons to the Mössbauer spectra.     

Intermediate coupling model description of55Fe and57Fe

The properties of the negative parity states of⁵⁵Fe and⁵⁷Fe are investigated in the framework of the intermediate coupling model. In the model, a neutron or a quasineutron is coupled to anharmonic vibrations of the core. Anharmonicities of the vibrations are estimated through the observed properties of the core. Energy levels, spectroscopic factors and electromagnetic properties have been calculated. The results of the present calculations are also compared with available experimental results and other theoretical results. The model reasonably accounts for many of the properties of the low-lying states.     

CEMS and DCEMS investigations of Al-implanted iron

-Fe surfaces were implanted with a nominal dose of 5×10¹⁷ Al ions/cm² at 50 keV and a current density of about 3.7 A/cm². Samples of different shapes and thicknesses have been used in order to test the influence of heat flow from specimen to target holder during implantation. Integral and energy differential (depth-selective)⁵⁷Fe conversion electron Mössbauer spectroscopy (CEMS and DCEMS) were employed. The spectra indicated a magnetic phase characterised by a broad hyperfine field distributionP(B _hf), a non-magnetic phase, and -Fe. The relative intensity of the non-magnetic phase was enhanced if the thermal contact during implantation became worse. An energy dependence of DCEM spectra in the L-electron range was observed. Model calculations using L-electron weight functions and experimental concentration profiles obtained by secondary neutral mass spectroscopy (SNMS) yielded fair agreement between calculated and experimental phase signals. The results demonstrate that the non-magnetic Fe-Al alloy phase with high Al concentration is located closer to the surface than the magnetic alloy phase, which extends to much larger depth than expected.     

57Fe Mössbauer study of Fe nitrides

Summary Magnetic properties of Fe nitrides have been re-examined by⁵⁷Fe M?ssbauer spectroscopy. Hyperfine magnetic fields for α″-Fe₁₆N₂ are 30, 31 and 39T at 298K, but the averaged hyperfine field is 33T and nearly equal to the value of pure α-Fe. σ-Fe₂ N is an antiferromagnet below 9K having a small magnetic moment less than 0.1 μ_B, although γ′-Fe₄N and ε-Fe_3–2N are ferromagnets. ZnS-type FeN is non-magnetic at 4.2K. M?ssbauer spectra obtained from NaCl-type FeN are complex and some Fe atoms in this nitride show a surprisingly large hyperfine magnetic field of 49T. Paper presented at the ICAME-95, Rimini, 10–16 September 1995.     

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.     

α-57Fe spectra only

It is the intention of this contribution to demonstrate how polarization-and thickness effects-are reflected on the most common Mössbauer material: α-Fe.     

Untersuchungen an Neutronenresonanzen im57Fe

The total neutron cross section of⁵⁷Fe in the keV region was measured in a transmission experiment using a pulsed Van de Graaff generator. Experimental data were fitted with a two channel multilevel formula to obtain the individual resonance parameters including the inelastic scattering width. The strength-function and its spin dependence are investigated. The data indicate a correlation between the phases of the reduced amplitudes for elastic and inelastic scattering. In a further experiment the 14,4 keV-γ-radiation of the (n, n′ γ)-reaction in⁵⁷Fe was detected. The application of this reaction for Möβbauer experiments is discussed.     

Maxwellian Averaged Neutron Capture Cross Sections in 56Fe and 57Fe

Measurements of the keV-neutron capture cross sections and radiative γ-ray spectrum of 56Fe and 57Fe are performed based on a 7 Li（p,n）7 Be reaction neutron source. The incident neutron spectrum on a capture sample is measured by means of a time-of-flight （TOF） method with a 6Li-glass detector. The radiative capture 7-rays emitted from an iron CS Fe or 57 Fe） or standard gold （197Au） sample are detected by a large anti-Compton NaI（TI） spectrometer covered with a heavy shield. The capture yields of samples are obtained by applying a pulse-height weighting technique to the corresponding capture γ-ray pulse-height spectrum. The Maxwellian averaged neutron capture cross sections of 56Fe and 5T Fe are derived according to the present capture cross section results.     

NMR of Fe57 in lithium ferrite

An apparatus is described for studying NMR of Fe⁵⁷ and Ni⁶¹ in various ferromagnets and ferrimagnets. The NMR of Fe⁵⁷ was observed in lithium ferrite at room temperature. The magnitude of the NMR signal was studied as a function of the external magnetic field, and the signal was found to fall off more rapidly than the permeability with the applied field. The NMR signal of Fe⁵⁷ in lithium ferrite is apparently amplified by domain-boundary motion.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 10, pp. 62–66, October, 1970.     

Study of the57Fe low-energy states

The low energy states of⁵⁷Fe has been studied by means of thermal neutron radiative capture. The gamma-ray spectrum below 3 MeV was measured using a Ge(Li) detector of an intrinsic volume 5.4 cm³. On making use of other experiments beside the good resolution of the Ge(Li) detector it was possible to suggest a decay scheme and to get some valuable informations. The transitions from the levels 366.7keV to the ground- and first-excited states seem to be pureM1 transitions. An evidence for the existence of a transition from the level 1725.5 keV to the 1018.6 keV with an absolute intensity 2.4% is shown.     

57Fe Mössbauer study of Fe/Bi multilayers

Fe/Bi artificially structured films (ASF's) have been prepared by alternate depositions of Fe and Bi in an ultrahigh vacuum. X-ray diffraction measurements in the small angle range confirmed the formation of periodic structures in all the samples prepared on glass substrates cooled down to about 125K. the CEMS at room temperature indicated that the samples are ferromagnetic except the one with 2Å-thick Fe layers. The CEM spectra also indicated that the structure of Fe layers is amorphous when the Fe layer thicknesses are less than 15Å. Magnetization measurement and CEM spectrum at 6K show that Fe monolayers in the Fe/Bi ASF are ferromagnetic.     

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.     

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.     

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.     

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.