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We investigated Fe-phases of iron complexes embedded in nonfunctionalized (as-prepared) and functionalized multi-wall carbon nanotubes (MWCNTs). Mossbauer spectroscopy is a very sensitive tool to study chemical states of iron compounds embedded in MWCNTs. It showed that the chemical treatment of the as-prepared MWCNTs caused release of about 84% of iron and modification of the remaining iron compounds. In as-prepared and carboxylated MWCNTs almost 80 and 75% of iron complexes in a form of Fe3C exhibited magnetic ordering even at room temperature, respectively. In MWCNT-COONH4 only 50% of such iron compounds showed local magnetic ordering. In all cases about 2% of magnetic α-Fe fraction was detected. Through the dc magnetization and transmission electron microscopy (TEM) measurements it was proved that cementite nanoparticles formed agglomerates and their sizes were larger than 10 nm. STM measurements indicated increased homogeneity of the surface electric properties in the case of chemically treated carbon nanotubes.

Different forms of iron compounds embedded in non-functionalized (as prepared) and functionalized multiwall carbon nanotubes (MWCNTs) were studied. Iron used to catalyze MWCNT synthesis can be found inside nanotubes and built-in within their walls. Mossbauer spectroscopy was applied to study valence and spin states as well as magnetic ordering of the iron compounds. In the Mossbauer spectra of as prepared MWCNTs the Fe3C carbide provides the main contribution. The content of Fe3C decreases by about 20 and 40% in carboxylated carbon nanotubes (MWCNTs-COOH) and ammonium salt of carboxylated carbon nanotubes (MWCNTs-COONH4), respectively. A small amount of α-Fe and FexCx iron forms are always observed in all studied carbon nanotubes. In MWCNTs-COOH, additionally, ferrihydrates and/or FexCy with oxygen in the second coordination sphere of iron are present (at a level of about 17%). In MWCNTs-COONH4 their content increases by a factor of 3. The experimental data shows that the purification and functionalization of as prepared MWCNTs result in removal of about 90% of iron contaminations. Additionally, we observe the modification of iron compounds inside MWCNTs. All these results are important in optimizing the as prepared MWCNT purification process and in finding a new way to produce different Fe phases inside MWCNTs.

The potential applications of carbon nanotubes (CNTs) are strongly related to their physical and chemical properties. In this work, results of different methods for the oxidation of crude CNTs are reported. These methods changed Fe binding sites within multiwall carbon nanotubes (MWCNTs). Mossbauer spectroscopy was used to detect the chemical properties of the Fe-phases in MWCNTs. Signals from the iron carbide Fe3C were the main components in the Mossbauer spectra of unmodified MWCNTs revealing magnetic ordering even at 300 K. In oxidized MWCNTs, the amount of Fe3C decreased and γ-Fe and α-Fe, ferrihydrates of iron oxides and different forms of goethite appeared. In MWCNTs oxidized with HClO4, a significant fraction (∼24%) of magnetically ordered Fe2O3 particles was detected. This study showed that traces of iron catalyst embedded in MWCNTs could be used as a sensitive probe to monitor various MWCNT modifications.

The Kerr magnetometer with differential amplifier which in contrast to lock-in detection technique, is especially recommended for rapid measurements up to 1.5 kHz is described. The calibration of the Kerr rotation angle was performed on the standard sputtered films (with thickness from 2 nm to 50 nm) and Fe-wedge sample, prepared by MBE-technique, in the range of thickness from 1ML to 50 ML of Fe. The test measurements on spin valve structure were also performed.

Ultrathin cobalt films and wedges in gold envelope Au/Co(d Co 0) were determined for samples with different thicknesses. Annealing induced in the sample: (i) flattening of the cobalt surface; (ii) a decrease of the coercivity field and magnetic anisotropy caused a decrease of thickness of reorientation from easy axis state to easy plane one; (iii) an increase of the Barkhausen volume which contains many cobalt islands creating the chains. Approaching the reorientation region, the character of the magnetization reversal drastically changes from that with the preference of domain wall propagation into the one connected to the domain wall nucleation.

Ultrathin Fe(001) films, of 1-3 atomic layers, were grown on the Au(001)-hex surface by molecular beam epitaxy. The film growth was controlled in situ by LEED and STM. At the initial stages of the iron growth, a monolayer of Au automatically diffuses onto the growing Fe film, preventing it from breaking up into islands. Conversion electron Mossbauer spectroscopy (CEMS) reveals considerable Au-Fe intermixing at the interface, which leads to formation of a two-dimensional alloy. The intermixing is also responsible for certain deterioration of the atomic order and the layer sequence in the artificial FeAu alloy obtained by alternative deposition of Fe(001) and Au(001) monolayers. CEMS data for single Fe films and Fe-Au monoatomic superlattices are compared and discussed basing on the FLAPW calculations using WIEN97 code.

Molecular beam epitaxy grown (001) oriented Cr/Fe/Cr and Cr/Fe/Cr/Fe/Cr sandwiches were characterized using the conversion electron Mossbauer spectroscopy (CEMS), which proved that the FeCr interface extended up to about 2.5 atomic layers. Analysis of the CEMS results was based on a simple alloy-model of the Fe/Cr interface, resulting in concentration profiles of Fe and Cr atoms. The derived interface model was then used to study the effect of thermal annealing on the film properties. The CEMS studies were correlated with the measurements of the indirect exchange coupling followed by the magneto-optic Kerr effect. Whereas CEMS revealed a measurable effect of annealing on the interface atomic structure for the annealing temperature T A = 200°C, the coupling character began to change at considerably higher temperature (about 400 °C).