Mössbauer Optimization of the Direct Synthesis of β-FeSi2 by Ion Beam Mixing of Fe/Si Bilayers

At present, there is an increasing interest in the iron di-silicide phase -FeSi₂, which is supposed to be a direct band gap semiconductor and one of the most promising materials for silicon-based optoelectronics, e.g., light-emitting devices, solar cells, and photo detectors. But this phase is very difficult to be produced. Here, the successful direct synthesis of this phase by ion beam mixing of Fe/Si bilayers at temperatures in the range of 400 to 600°C is reported. The aim of the experiments was to achieve a complete reaction of the deposited Fe layer with the Si substrate that results in the formation of a pure, single-phased -FeSi₂ surface layer. The obtained silicide layers, their structure and composition are investigated by conversion electron Mössbauer spectroscopy (CEMS), Rutherford backscattering spectrometry (RBS), and X-ray diffraction (XRD). The fraction of the -FeSi₂ formed is determined by CEMS as function of ion species, energy, fluence and temperature. Complete growth and formation of a single-phased -FeSi₂ layer was achieved by 205 keV Xe ion irradiation at a fluence of 2×10¹⁶ ions/cm² at 600°C.     

Mössbauer Study of the Fe3B/Nd2Fe14B Nanocomposite Magnet by the Addition of Co

The addition of Co to Nd₄Fe_77.5–x Co _x Hf_0.5Ga_0.5B_18.5 (0x5) was found to enhance the magnetic properties of Fe₃B/Nd₂Fe₁₄B nanocomposite magnets. The enhancement resulted from the fact that Co tends to retard the formation of Fe₃B from the amorphous matrix but to accelerate that of Nd₂Fe₁₄B. The decreased interval between the crystallization temperature of Fe₃B and Nd₂Fe₁₄B led to a uniform grain size distribution of both phases during the annealing treatment. The additive Co was confirmed to partition mainly to Nd₂Fe₁₄B crystals rather than to Fe₃B which was traced by XRD and Mössbauer spectroscopy as well. About 72 vol.% of Fe₃B, 27 vol.% of Nd₂Fe₁₄B, and a small amount of Fe around 1 vol.%, respectively, were found to form. However, the volume fraction of each phase did not vary by the addition of Co up to 5 at.%.     

Study of the dehydration of Portland Cement by Mössbauer spectrometry

Egyptian Portland Cement in the form of one inch cube was hydrated at different times of hydration. Nine cubes of each period of hydration were heated for five minutes 200, 300, 400 up to 1000°C then were quenched in air. The compressive strength was measured for these samples and related to unheated ones. These cubes were ground and measured by Mössbauer spectrometry to correlate the effect of dehydration of cement pastes on the states of iron, with the decrease of compressive strength. It was observed that starting from 400°C the central doublet characteristic of the hydration process decreased as the dehydration temperature was increased. At 1000°C the dehydration process was complete, the central doublet disappeared and the compressive strength vanished. The hydration process was found to be reversible. The application of Mössbauer spectrometry to estimate the degree of fire in concrete building was demonstrated.     

Mössbauer study of spatial dispersion of magnetization at Fe/Cr superlattice interfaces

From an analysis of Mössbauer CEMS spectra, it was found experimentally that a magnetic anisotropy field has an angular spatial dispersion at Fe/Cr superlattice interfaces, due to the roughness and inhomogeneity of the interlayer boundary. The value of the magnetoresistive effect is determined by the spatial dispersion of both the interface and the Fe layer, for which the deviation angle of the magnetization vector depends on the substrate irregularity.     

Atomic Force Microscopy Measurement of DNA Fragment Induced by Heavy Ions

Choosing ^7 Li and ^12C heavy ions respectively with different linear energy transfer (LET) values, purified plasmid DNA samples in aqueous solution are irradiated with various doses. The atomic force microscopy (AFM) is used for analysis of DNA fragments induced by both the kinds of heavy ions. There is a change of three forms of DNA, i.e. supercoiled, open circular and linear form, as the dose is observed. The distribution function of DNA fragment length is obtained for the first time and fitted with the Tsallis entropy statistical theory. The result indicates that AFM is a useful tool for analysis of the short fragment of DNA, high-LET heavy ion radiation induces DNA double strand breaks (DSBs) more effectively, and the distributions of the DSBs are more local and dense in comparison with low-LET radiation.     

Study of defects in Fe–Re and Fe–Mo alloys by the Mössbauer and positron annihilation spectroscopies

The room temperature positron annihilation lifetime spectra and ⁵⁷Fe Mössbauer spectra were measured for pure Fe as well as for iron-based Fe_1?xRe_x and Fe_1?xMo_x solid solutions with x in the range 0.01≤x≤0.05. The measurements were performed in order to learn more about creation of structural defects during formation and further mechanical processing of the iron systems under consideration. The spectra were collected at least twice for each studied sample synthesized in an arc furnace—after cold rolling to the thickness of about 40 μm as well as after subsequent annealing at 1270 K for 2 h. It was found that in the annealed samples positrons live much shorter than in the not annealed ones which suggest that the latter samples are more defected as it could be expected. Moreover simultaneous analysis of the positron and Mössbauer data shows that cold rolling leads to creation of two types of defects. It seems that they are dislocations and vacancies. Finally from the Mössbauer data it follows that vacancies are located mainly in the vicinity of non-iron atoms, Re or Mo. This speaks in favour of the suggestion that in iron matrix the impurities mentioned above and vacancies interact attractively which supports the known from the literature, theoretical calculations on the Mo-vacancy interaction in iron.     

Mössbauer study of magnetic Fe/FeSi multilayers

Many useful properties of magnetic multilayers depend on the coupling between the ferromagnetic layers. The coupling often oscillates with the thickness of non-magnetic spacer layers: it is ferro- or antiferromagnetic or even non-collinear near a critical thickness. We investigated the magnetron-sputtered Fe/FeSi multilayers with spacer thickness around 1.7 nm by means of Conversion Electron Mössbauer Spectroscopy with oblique incidence of the γ beam in order to gain information on the orientation of the local magnetic moments in the multilayer plane. The results show that the local moments make an angle of 45°–50° with the direction of the remanent magnetization. This is consistent with strong biquadratic coupling which in turn is expected at this spacer thickness from our magnetic measurements. An analysis of the distribution ofB _hf corresponding to different numbers of n.n. Si atoms in the bcc Fe structure points to weak diffusion of Si through the Fe/FeSi interface characterized by a diffusion length of about twice the substrate roughness.     

Mössbauer Study of Iron-Containing Carbon Nanotubes

⁵⁷Fe transmission Mössbauer at temperatures between 18 and 298 K and magnetic measurements have been used to characterize Fe-filled carbon nanotubes which were prepared by pyrolisis of Ferrocene + C₆₀ at atmospheric pressure under an Ar atmosphere at 1050°C. The Mössbauer data have shown that the Fe phases encapsulated within the carbon nanotubes are -Fe, Fe₃C and -Fe. The magnetic results are compatible with the Mössbauer data. Taken together the results allow us to propose a simple picture of the distribution of iron phases within the carbon nanotubes which would consist of an -Fe core surrounded by an -Fe shell, finally covered by an Fe₃C layer.     

Fe/Dy artificial multilayered films studied by57Fe Mössbauer spectroscopy

Magnetic properties of multilayered Fe/Dy films with artificial superstructures have been investigated by⁵⁷Fe Mössbauer spectroscopy. Doublet peaks are observed at room temperature when the Fe layer is thinner than 20Å. Mössbauer spectra for thicker Fe layers correspond to α-Fe spectra. In certain samples, i.e. [Fe(44Å)/Dy(6Å)], a gradual spin reorientation takes place, which is evidenced from the change of relative intensities of Δm=0 lines with decreasing temperature.     

238U and 57Fe Mössbauer Spectroscopic Study of UFe2

We have performed ⁵⁷Fe and ²³⁸U Mössbauer measurements of UFe₂ in order to investigate its magnetic properties. From the results of ⁵⁷Fe Mössbauer spectroscopy, the ferrromagnetic ordering at 167 K is caused by the iron 3d-electrons, which hybridize strongly with the uranium 5f-conduction electrons. It is also clarified from the results of ²³⁸U Mössbauer spectroscopy that there are no magnetic moments on the uranium atoms.     

Interface study of Ag/57Fe/Ag trilayer using Mössbauer and X-ray standing wave analysis

Interface of Ag/⁵⁷Fe/Ag trilayer has been studied with a depth resolution of a fraction of a nanometer using x-ray standing waves generated by a W/Si multilayer mirror used as a substrate. Two interfaces of 38 Å thick Fe layer in Ag/⁵⁷Fe/Ag trilayer are clearly resolved. It is found that the rms roughness of the two interfaces Fe-on-Ag and Ag-on-Fe are 10 ± 1.0 and 6 ± 1.0 Å, respectively. Conversion electron Mössbauer spectroscopy (CEMS) has been used to get information about the volume fraction of the intermixed region and the estimated roughness from the relative area of the two sextets of CEMS spectra is found to be 7.0 Å which is consistent with the average roughness obtained by X-ray fluorescence measurements. However, the asymmetry of the interfaces can not be inferred from CEMS measurements.     

A Study of Iron Phthalocyanine Pyrolyzate with Mössbauer Spectroscopy and Transmission Electron Microscopy

Physics of the Solid State - A pyrolyzate of iron phthalocyanine is studied by Mössbauer spectroscopy and transmission electron microscopy. The phase composition and magnetic state were found...     

57Fe Mössbauer study of Lu2Fe3Si5 iron silicide superconductor

With the advent of Fe–As based superconductivity it has become important to study how superconductivity manifests itself in details of ⁵⁷Fe Mössbauer spectroscopy of conventional, Fe-bearing superconductors. To this end, the iron-based superconductor Lu₂Fe₃Si₅ has been studied by ⁵⁷Fe Mössbauer spectroscopy over the temperature range from 4.4 K to room temperature with particular attention to the region close to the superconducting transition temperature (T_c=6.1 K). Consistent with the two crystallographic sites for Fe in this structure, the observed spectra appear to have a pattern consisting of two doublets over the whole temperature range. The value of Debye temperature was estimated from temperature dependence of the isomer shift and the total spectral area and compared with the specific heat capacity data. Neither abnormal behavior of the hyperfine parameters at or near T_c, nor phonon softening were observed.     

Synchrotron Mössbauer source of57Fe radiation

A nonradioactive source of Mössbauer radiation is described for use in Mössbauer absorption and scattering spectroscopy. The radiation is generated by synchrotron Xrays in an iron borate single crystal set in diffraction conditions at the Néel temperature (75.3°C). Like a conventional Mössbauer source the new Synchrotron Mössbauer (SM) source emits singleline radiation of about natural linewidth, but in addition the emitted radiation is fully recoilless, highly directed and of pure linear polarization. An extremely high suppression of the electronic scattering is achieved. The latter circumstance allows one to perform Mössbauer experiments using pulsed synchrotron radiation in a steady state mode as in a normal Mössbauer measurement.The theory of the SM source is developed. First Mössbauer spectra obtained with the SM source are shown. Applications of the SM source are discussed.     

Mössbauer Spectroscopy Study of Iron Nickel Alloys

Three samples of Fe_100–x Ni _x (with x=30, 35 and 40) were prepared by arc melting technique. The Mössbauer spectra of the three samples were collected and analyzed. The spectrum of the sample with x=30 consists of a singlet and a sextet. The singlet component which has isomer shift (IS=–0.08 mm/s) is attributed to a superparamagnetic phase. The value of the magnetic hyperfine field associated with the sextet component, 34.0 T, is consistent with that of -Fe–Ni alloy. In the spectra of the other samples the central line disappears. The magnetic component, used in fitting the spectrum of the sample with x=40 has a hyperfine magnetic field B _hf=30.0 T. This component is assigned to the high-spin -FCC Fe–Ni phase. Two magnetic components of 16.3 T and 27.3 T are used to fit the spectrum of the sample with x=35. The 27.3 T component is associated with the typical high-spin -FCC Fe–Ni phase while the 16.3 T component is associated with a -FCC Fe–Ni phase with magnetic relaxation.     

Mössbauer Study of Magnetic FeSb Dilute System

Hyperfine Interactions - Mössbauer study of semimetals is of great importance in understanding the origin of hyperfine interactions in these materials. A concentration dependence study in Fe x...     

Mössbauer Study of Multiple Substitutions in YBCO

Hyperfine Interactions - Mössbauer studies of multiple substitutions in YBCO with general formula (Y1?Z Ca Z )Ba2(Cu1?X?Y Fe Y M X )3O7?δ are reported. XRD has...