Anomalous behavior of the Debye temperature in Fe-rich Fe-Cr alloys

Debye temperature, $\Theta_D$, of Fe-rich Fe$_{100-x}$Cr$_x$ disordered alloys with $0\le x \le 22.3$ was determined from the temperature dependence of the central shift of M\"ossbauer spectra recorded in the temperature range of 60 -- 300 K. Its compositional dependence shows a maximum at $x \approx 5$ with a relative increase of $\sim 30$% compared to a pure iron. The composition at which the effect occurs correlates well with that at which several other quantities, e. g. the Curie temperature and the spin-wave stiffness coefficient, $D_0$, show their maxima, but the enhancement of $\Theta_D$ is significantly greater and comparable with the enhancement of the hyperfine field (spin-density of itinerant $s$-like electrons) in the studied system. The results suggest that the electron-phonon interaction is important in this alloy system

Effect of time and storing conditions on iron forms in ferrous gluconate and Ascofer

Antianemic medicament Ascofer and ferrous gluconate, its basic iron bearing ingredient, were studied with the use of Mossbauer spectroscopy. Room temperature spectra gave a clear evidence that two phases of iron were present viz. ferrous (Fe2+) as a major one with a contribution of 85+-5%, and ferric (Fe3+) whose contribution was found to be 15+-5%. However, the actual values of the contributions of the two kind of the iron ions in Ascofer depend on sample's age: the abundance of Fe2+ ions increases with time by 10% after 51 months, while that of Fe3+ decreases by the same amount. This means that an internal reduction of Fe3+ ions takes place. Ferrous ions were shown to occupy at least two different sites. In Ascofer, the relative abundance of the two sites does not depend on the age of sample, while in the gluconate the population of site 1 increases and that of site 2 decreases with the age of the sample.Comment: 14 pages, 13 figure

Relationship between the magnetic hyperfine field and the magnetic moment

Based on experimental data it is shown, for some chosen alloys and compounds of iron, that there is no one unique relationship between the 57Fe-site magnetic hyperfine field, Bhf, and the magnetic moment per Fe atom, m. Instead, the Bhf-m plot consists of several branches, each of them being characteristic of a given alloy or compound. Consequently, the effective proportionality constant (hyperfine coupling constant) depends on the alloy system or compound, and for a given alloy system or compound it depends on the composition or even on the lattice site. Consequently, the scaling of Bhf into the underlying m cannot be done a priopri

INFLUENCE OF NEIGHBOURING CHROMIUM ATOMS ON HYPERFINE FIELDS AT 57Fe NUCLEI AND ISOMER SHIFTS IN Fe-Cr ALLOYS

En utilisant plusieurs modèles différents on a montré que parmi les modèles en deux couches employés pour lisser les spectres Mössbauer des alliages Fe-Cr, le mieux approprié est celui qui inclut uniquement les contributions des atomes de Cr situés dans les deux premières sphères de coordination. Utilisant ce modèle pour lisser les spectres Mössbauer d'alliages Fe-Cr avec différentes concentrations de chrome (1-15 at % Cr) on a montré que la variation du champ magnétique hyperfin au site de 57Fe(ƊH1) produite par une impureté dans la première sphère de coordination est supérieure à celle (ƊH2) produite par une impureté qui est un second proche voisin. Le rapport R = ƊH1/ƊH2 dépend de la concentration et les lissages par moindre carré de nos données montrent qu'on peut le mettre sous la forme R = 1,24 + 0,03 c pour le modèle M 12 ou R = 1,24 + 0,02 c pour le modèle M 12 BW. On a aussi étudié le problème de l'additivité des effets dus aux atomes de Cr aussi bien sur les champs magnétiques hyperfins au site des noyaux 57Fe que sur les déplacements isomériques. On observe une additivité partielle et totale pour le champ magnétique hyperfin, alors que pour le déplacement isomérique il n'y a qu'une additivité totale avec d'assez grandes erreurs expérimentales.Using several different models it has been shown, that among the two-shell models employed for fitting the Mössbauer spectra of Fe-Cr alloys the most adequate is the one, which includes only contributions from those Cr atoms which occupy the first two coordination spheres. Employing then this model for fitting the Mössbauer spectra of Fe-Cr alloys having different chromium concentration (1-15 at % Cr) it has been revealed, that the change of the hyperfine magnetic field at 57Fe nuclei, ƊH1, due to an impurity atom in the first coordination sphere is higher than the change, ƊH2, due to a second-nearest neighbour impurity. The ratio R = ƊH1/ƊH2 turns out to be concentration dependent and least-squeres fits to Our data show that it may be expressed as R = 1.24 + 0.03 c for the M 12-model or R = 1.24 + 0.02 c for the M 12 BW-model. The problem of the additivity of the observed effects of Cr atoms both on the hyperfine magnetic fields at 57Fe nuclei and on the isomer shifts was also investigated. For the hmf partial and total additivity is observed, whilst for the IS only total additivity occurs within rather high experimental errors