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First we studied the kinetics of the formation of Ba monoferrite by means of Mossbauer spectroscopy. The most important result is the considerable portion of hexaferrite existing after treatment of the starting materials between 800 and 900°C, caused by a higher rate of diffusion of the Ba2+ ions in comparison to the Fe3+ ions. Second we report susceptibility measurements recorded in a temperature range of 4.3 K to 280 K and Mossbauer spectra at room temperature and at 4.2 K without and in the presence of an applied magnetic field of 6 T. The experimental data demonstrate that the magnetic behaviour of Ba monoferrite deviates to some extent from a simple antiferromagnetic.

Etude des structures magnetiques de BaFe 12 O 19 et de BaCo 0.8 Ti 0.8 Fe 10.4 O 19 par spectroscopie Mossbauer de Fe 57 . Analyse de la variation du spectre Mossbauer avec la temperature et le champ magnetique applique. Interpretation des resultats en termes d'inversion du spin du reseau, du a l'influence des ions Co 2+

The 57 Fe Mossbauer resonance has been applied to study polyacetylene films doped chemically and electrochemically to different doping levels. Both methods lead to the insertion of a high spin Fe III complex with Mossbauer parameters characteristic of FeCl − 4 . Degradation of [CH(FeCl 4 ) y ] x in air leads to gradual transformation of Fe III into a high spin Fe II .

Mesure de la susceptibilite magnetique du monoferrite Ba (BaFe 2 O 4 ) entre 4,3 et 280K, et des spectres Mossbauer a l'ambiance et a 4,2K avec et sans champ magnetique applique. Existence d'une contribution ferrimagnetique a l'ordre magnetique de BaF 2 O 4 a basse temperature due aux couches cristallographiques magnetiquement differentes de la structure

Several Mossbauer studies of Ti-Fe spinels have been reported in the literature for x ≦ 0.8 (BANERJEE et al.; VANLEERBERGHE et al.) or for x ≦ 0.05 (UMEMURA et al.). BHADURI measured the Mossbauer spectra of the whole system (0 ≦ x ≦ 1) and suggested that TixFe3−xO4 samples with x 0.6 may be regarded as n-type semiconductors with localized electrons. We present measurements of electrical properties and Mossbauer spectra of synthetic TixFe3−xO4 single crystals with x = 0; 0.24; 0.5; 0.72. It is seen that the electronic behaviour strongly depends on the content of titanium. At a composition of approximately x = 0.65 a transition from n- to p-type of electrical conductivity occurs. 57Fe Mossbauer data of the samples for different temperatures obtained of the spectrum computer analysis using a least squares fit program are given. The Mossbauer spectra below and above the Neel temperature demonstrate the distinct decrease in mobility of electrons in dependence on the Ti content. It is evident from the Mossbauer spectrum of the sample Ti0.72Fe2.28O4 recorded above the Neel temperature that Titanium is incorporated into the spinel structure of this system only in a four valent state.

Doping of polyacetylene with iron chloride complexes has been studied by MBssbauer spectroscopy. It was proved that the doped polymer undergoes degradation in air manifested by the formation of FeOlxaE^O with the simultaneous chlorination of the double bond.

Very active catalysts can be prepared from FeCl3-GIC precursors through a two-step reduction and washing with HCl. Mossbauer spectrometry during the first (H2) reduction step indicates that Fe0 in the form of α-Fe is obtained together with two non-equivalent FeII sites. This α-Fe is catalytically inactive and can be readily removed from the system treatment with HCl. The second reduction with potassium vapour transforms the remaining FeII into catalytically active Fe0 which is strongly resistant to the HCl treatment.

The hyperfine interaction parameters at the 161Dy and 57Fe nuclei in Dy2−yYyFe17 compounds (0⩽y⩽2) have been determined from the Mossbauer effect measurements at 4.2 K. The dysprosium atoms are substituted by the yttrium atoms across the series and then the 5d electrons of Dy are replaced by the 4d electrons of Y. The hyperfine interaction parameters for both nuclei remain constant versus Y content. The full equivalency between 5d and 4d electrons has been deduced. The excess of the hyperfine magnetic field at the 161Dy nuclei and the reduction of the magnetic hyperfine field at the 57Fe nuclei can be explained as a result of the presence of the magnetically polarized 5d (or 4d) electrons in these compounds.