Study of Mg2Ni1−xFex alloys by Mössbauer resonance
Résumé
After preparing Mg2Ni1−xFex (x=0.005, 0.01, 0.02 and 0.08) alloys, they were studied by Mössbauer resonance. The Mössbauer spectra of x=0.005 and 0.01 alloys exhibit two doublets (doublet 1, 2). That of x=0.02 alloys shows two doublets (doublet 1, 2) and one sextuplet, and that of x=0.08 alloy has only one sextuplet. Doublet 1 for x=0.005, 0.01 and 0.02 alloys is considered to result from a fraction of Fe in excess showing a superparamagnetic behavior. Doublet 2 is considered to result from the Fe substituted for Ni in the Mg2Ni phase. The values of isomer shift 0.25–0.29 mm/s suggest that the iron exists in the state Fe+3. The result that the quadrupolar splitting of doublet 2 is not zero shows that the distribution of electrons around the iron is asymmetric. Their values for the doublet 2, 1.21–1.39 mm/s, approach the value of quadrupolar splitting for the oxidation number +3. The sextuplet showing the magnetic hyperfine interactions results from the iron, which has not substituted the nickel in the Mg2Ni phase. The Mössbauer spectrum of the x=0.01 alloy hydrided at 723 K shows one doublet and sextuplet. The segregation of Fe is considered to result from the reaction of the Mg2Ni phase with the oxygen contained in the hydrogen as impurity...