CEMS study of oxide layers formed on stainless steel (SUS304 and SUS316)

Stainless steel (SUS304 and SUS316) was chemically treated and heated at various temperatures, and the oxide films formed on the surface were analyzed by conversion electron Mössbauer spectrometry (CEMS). Three magnetic components of iron species were detected in the top oxide layers of stainless steels heated below 600°C and the fine particles of iron oxides were initially produced in the inner oxide layers of the samples heated at temperatures higher than 700°C. Only paramagnetic iron species were detected in the oxide layers of the stainless steels prepared by chemical treatment.     

Onset of magnetization in monolayer films

Correlations between structural and magnetic properties for ultra-thin iron films are discussed. Some selected methods of structural and magnetic analysis are reviewed. The onset of magnetism for submonolayer Fe(110) film on W(110) is explained based on STM (scanning tunneling microscopy) imaging. Hyperfine magnetic fields in iron films sandwiched between Cr show unusual temperature behavior due to the influence of magnetic ordering in Cr. Magnetic properties of metastable iron phases on Cu and Ru are discussed, based on CEMS measurements.     

Thermal oxidation behaviors and structures of Fe-9Cr-1Mo alloy

Isothermal oxidation behaviors of Fe-9Cr-1Mo alloy were investigated at 600, 700, 750 and 850 ^°C for 72 h in air atmosphere. The oxidation rates were measured using a thermogravimetric analyzer (TGA). The structure and composition of the oxide scale were characterized by X-ray diffraction (XRD), energy dispersive spectrometry (EDS) and conversion electron Mössbauer spectrometry (CEMS). In this study it was found that the oxide layers form duplex structures consisting of Fe and Cr oxides. CEMS spectra are composed of one doublet due to dispersed Fe ³⁺ in Cr₂O₃ oxidation layers produced at high temperatures and two magnetic components due to Fe-Cr-Mo alloy substrate and hematite (Fe, Cr)₂O₃ with lower hyperfine field than pure hematite (52 T). Fe rich oxides are formed at the surface by oxidation at relatively low temperatures of 600 ^°C and 700 ^°C, while Cr rich (Fe, Cr)-oxides are formed in the top surface layers by oxidation at higher than 750 ^°C.     

Mössbauer-Effect Study of Metastable c-FeSi Synthesized by Molecular Beam Epitaxy (MBE) and by Ion Implantation

Conversion electron Mössbauer spectroscopy (CEMS) has been applied to the study of the metastable c-FeSi phase (i.e. an iron silicide with CsCl lattice structure) that was synthesized by implantation of Si + ions of 50 keV in energy into f -Fe (95% 57 Fe) near room temperature with a nominal dose of 5 2 10 17 cm m 2 , and by molecular beam epitaxy (MBE). Iron silicide layers with different stoichiometry (FeSi 0.85 , FeSi, Fe 0.85 Si) were grown by codeposition of 57 Fe and Si onto an Fe buffer layer on MgO(100). For all FeSi layers the defective CsCl structure was observed after annealing at different temperatures. X-ray diffraction measurements were performed to determine the structure and epitaxial relationship of the c-FeSi films. The lattice parameter perpendicular to the film plane was found to be 2.77(5) Å. CEMS measurements revealed a lower than cubic site symmetry of the iron atoms for both the c-FeSi layers synthesized by ion implantation and by MBE. The formation of nearly undistorted c-FeSi after annealing is favored by excess Fe atoms in the deposited film.     

Preparation and characterisation of electrodeposited amorphous Sn-Co-Fe ternary alloys

Electrochemical deposition was investigated as a process to obtain alloys of Sn-Co-Fe, which to date have not been reported in the literature. A constant current technique was used to electrochemically deposit tin-cobalt-iron alloys from a gluconate electrolyte. The gluconate system was chosen as an electrolyte, which could potentially provide an environmentally safe process. The effect of plating parameters such as current density, deposition time, temperature and pH are discussed. Results are reported for current density and plating time using an electrolyte temperature of 20-60 °C and pH of 7.0 in relation to phase composition, crystal structure and magnetic anisotropy of the deposited alloys.Investigations were conducted using ⁵⁷Fe conversion electron Mössbauer spectroscopy (CEMS), ¹¹⁹Sn CEMS, transmission Mössbauer Spectroscopy and XRD. The ⁵⁷Fe and ¹¹⁹Sn CEMS spectra and XRD showed that the dominant phase in the deposits was amorphous Sn-Co-Fe. The relative area of the 2nd and 5th lines of the sextets representing the magnetic iron containing phases was found to decrease continuously with increasing current density while at the same time no significant changes in the magnetic anisotropy was found with plating time. Magnetically split ¹¹⁹Sn spectra reflecting a transferred hyperfine field were also observed.A range of good quality amorphous Sn-Co-Fe ternary alloys was obtained over a range of operating conditions from an environmentally acceptable gluconate electrolyte.     

The effect of peptone on the structure of electrodeposited Sn-Fe binary alloys

Sn-Fe thin films were electrodeposited by constant current deposition on copper substrates using an aqueous gluconate based electrolyte with varying concentrations of the organic additive peptone. Good quality metallic deposits were obtained with surface morphologies which varied with the concentration of peptone present in the electrolyte. The effect of peptone concentration on the deposition process was studied using electrochemical polarization curves and EDX analysis. The effect of peptone concentration on deposit structure and surface morphology was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and ⁵⁷Fe and ¹¹⁹Sn conversion electron Mössbauer spectroscopy (CEMS). It was concluded that the addition of small amounts of peptone to the electrolyte slightly increased the bath stability and led to changes in the alloy composition of the electrodeposits. It was found that increases in the peptone content increased the amount of the crystalline structure in the deposits with corresponding reductions in the amounts of amorphous structure present in the deposits.     

CEMS characterisation of Fe/high-κ oxide interfaces

The interfaces between Fe and different high-κ oxides are investigated by means of conversion electron Mössbauer spectroscopy (CEMS). Information on the magnetic ordering at the interface is obtained from the magnetic hyperfine splitting of the Mössbauer spectra. The reactivity of the Fe atoms at the interface (intermixing) is also estimated by CEMS. X-ray diffraction (XRD) and X-ray reflectivity (XRR) provide additional information on the intermixing and different phases present at the interface. CEM-spectra show the presence of both ferromagnetic and paramagnetic phases. CEMS and XRD results show that the Fe/HfO₂ and Fe/Al₂O₃ interfaces are the least reactive. The degree of intermixing between Fe and the high-κ oxide is determined by the oxide surface roughness.     

Characterization of oxide layers and interface layers of ferrite stainless steel (SUS430) by57Fe CEMS

The oxide layers on stainless steel formed by heating at various high temperatures and by dipping in LiF + BeF₂ molten (Flibe) bath at 600 °C were characterized by CEMS. Hematite was a major iron product at 600 °C and fine oxides with paramagnetic Fe(III) species were produced at the higher temperatures than 700 °C. The interface of stainless steel beneath oxide films was characterized as the hyperfine field distributions. Paramagnetic Fe(III) species were produced on Cr depleted layers in the Flibe bath. CEMS is effective for simultaneous characterization of both oxide surface and interface layers of the ferritic stainless steel.     

Structure of sputter-deposited Pt/Fe and Cr/Fe multilayers

Conversion electron Mössbauer spectroscopy (CEMS) and X-ray diffraction (XRD) have been used to investigate the structure of Pt/Fe and Cr/Fe multilayers deposited by magnetron sputtering. The Cr/Fe samples consisted of four samples prepared under Ar sputtering pressures of 1.3, 3.0, 5.0, and 10.0 mT, all with the same multilayer structure of 3.5 nm Cr/2.5 nm Fe, repeated 35 times onto c-Si wafer substrates. The quality of the interfaces between Cr and Fe is clearly degraded with increasing sputter pressure, as seen by changes in the relative intensities of four magnetic subspectra in the CEMS and the gradual appearance of a single-line resonance similar to Fe in solution in Cr. The low-angle XRD superlattice peaks also disappear with increasing sputter pressure, while the high-angle XRD shows a tendency for loss of the preferred (110) texture. Two films of Pt/Fe were deposited epitaxially onto MgO single crystals with bilayer periods of 1.3 nm and 2.6 nm and total thickness of 300 nm each. A transition from fcc-PtFe with near-perpendicular magnetic anisotropy to a bcc-Fe/fcc-PtFe mixture with in-plane magnetic texture is observed by CEMS for the factor of two increase in bilayer period.     

Mössbauer and XRD study of novel quaternary Sn-Fe-Co-Ni electroplated alloy

Constant current electrochemical deposition technique was used to obtain quaternary alloys of Sn-Fe-Co-Ni from a gluconate electrolyte, which to date have not been reported in the literature. For the characterization of electroplated alloys, ⁵⁷Fe and ¹¹⁹Sn Conversion Electron Mössbauer Spectroscopy (CEMS), XRD and SEM/EDAX were used. XRD revealed the amorphous character of the novel Sn-Fe-Co-Ni electrodeposited alloys. ⁵⁷Fe Mössbauer spectrum of quaternary deposit with composition of 37.0 at% Sn, 38.8 at% Fe, 16.8 at% Co and 7.4 at% Ni displayed a magnetically split sextet (B = 28.9T) with broad lines typical of iron bearing ferromagnetic amorphous alloys. Magnetically split ¹¹⁹Sn spectra reflecting a transferred hyperfine field (B = 2.3T) were also observed. New quaternary Sn-Fe-Co-Ni alloys were successfully prepared.