Zs. Kajcsos

Magnetic hyperfine fields near the Fe / Cr (100, 110) interface studied by CEMS

Abstract Magnetic hyperfine (hf) fields near the Fe/Cr-interface in epitaxial thin film structures with (110)- and (100)-orientation were analyzed by means of in situ conversion electron Mossbauer spectroscopy (CEMS). The hf field at room temperature in the first Fe-monolayer (ML) at the interface is strongly reduced to 22.0 T (110) and 20.9 T (100) compared with the Fe-bulk value of 33.4 T. In contrast, in the second and third Fe-monolayer with respect to the interface the hf field was enhanced by 0.3 T to 33.7 for both film orientations.

A new spectrometer for Time-Differential Mössbauer Emission Spectroscopy (TDMES)

Abstract A new spectrometer for time-differential Mossbauer spectroscopy was developed featuring high count rate capability, good time resolution, and flexible data handling.

An electron spectrometer for depth selective conversion electron Mössbauer spectroscopy

Abstract A spectrometer has been constructed for depth selective conversion electron Mossbauer spectroscopy using an electrostatic cylindrical mirror analyzer. The spectrometer allows depth selective investigations even of samples with 57Fe in natural abundance. This was demonstrated on an Fe78B11Si9C2 amorphous metglas where the magnetic hyperfine field and the orientation of the magnetization was determined in dependence of the distance from the sample surface.

Improvements in 57Fe depth-selective conversion electron Mössbauer spectroscopy by applying a low-noise scintillation electron detector

Abstract A low-noise scintillation counter has been developed for the detection of low-intensity, low-energy (several keV) electrons in high vacuum. Performance comparisons with a channeltron for 57 Fe depth-selective conversion electron Mossbauer spectroscopy (DCEMS) show a substantial improvement in counting time in favour of the scintillation detector.

Free-volume studies in polyurethane membranes by positron annihilation spectroscopy

Abstract The free-volume parameters in various urethane/urea membranes obtained by varying the ratio of the structural constituents, polypropylene oxide and polybutadiene, were studied by positron lifetime and Doppler broadening measurements. On bi-soft segment membranes, a correlation was found between the composition of membranes, the normalized free volume, the radii of the holes and gas permeability. However, the correlation is not clear when PU data are also considered, indicating that other features must also play an important role in the permeation mechanism.

Icems and dcems study of Fe layers evaporated onto Al and Si

Thin layers of57Fe (2.5 nm, 10 nm and 70 nm thickness), vacuum evaporated onto Al and Si plates, have been investigated by conversion electron Mössbauer spectroscopy (CEMS). The measurements were performed employing both a proportional counter and a channeltron for conventional and ultrahigh-vacuum integral CEMS (UHV-ICEMS) studies, respectively, and a channeltron for depth-selective CEMS (DCEMS). The phase analysis of the layers on base of experimental results has indicated the presence of metallic iron and one or two iron compounds, ascribed to iron reaction products formed with the residual gas during evaporation. These products are most likely rather stable iron nitrides, are more or less clustered and are distributed throughout the whole layer.

CEMS-study of the interface in Fe/Cr multilayer systems

The magnetic hyperfine (hf.) fields at the Fe/Cr interface were analyzed in epitaxial Fe/Cr thin film structures of (100)- and (110)-orientation with monolayer resolution by means of in-situ57Fe Conversion Electron Mössbauer Spectroscopy (CEMS). The hf. field (300 K) in the 1st Fe-monolayer (ML) at the interface has been found to be strongly reduced to 22.0/20.9 T for (110)-/(100)-orientation, whereas the 2nd and 3rd ML reveal a slightly increased hf. field of 33.7 T as compared with the Fe-bulk value of 33.4 T. The temperature dependence of the hf. field at the interface shows aT3/2 spin wave law. The spin wave parameters are enlarged with respect to the bulk value indicating a reduced exchange interaction. A discontinuity in theT3/2-dependence is interpreted by the onset of magnetic order (Néel-temperature) of the Cr layers adjoining the57Fe probe layer.

Time-differential Mössbauer emission spectroscopy: Development of a new spectrometer and first results

A spectrometer for time-differential Mössbauer spectroscopy was developed with a high count rate capability, a good time resolution, and a flexible data handling. Chemical and physical aftereffects following the57Co decay were studied within the cobalt doped systems Turnbulls blue and ZnS.

Positron lifetime measurements in aliphatic hydrocarbons

The positron lifetimes and relative intensities were measured in highly purified liquid and solid hydrocarbons. It was found that most of the lifetime parameters changed at the melting point of the samples and their values were lower in the solid than in the liquid phase. A study of hexane isomers was also performed.

Criteria for optimizing dcems

As depth-selective conversion electron Mössbauer-effect measurements present a difficult task in Mössbauer spectroscopy due to the long recording times involved, the shortening of the measuring times is of major practical importance. Possible improvements of the overall experimental performance and measuring time gains due to efficiency increase and back-ground reduction will be analyzed; advantages of a scintillation counter over a channeltron for57Fe DCEMS applications will be discussed.