Resumo

PACHIN, Wilber et al. STRUCTURAL AND MAGNETIC PROPERTIES OF DISORDERED CRYSTALLINE Fe₅₀Mn_25+xSn _{25 - x} ALLOYS WITH x = -1.25, 0.0, 2.5, 5.0, 7.5. Momento [online]. 2021, n.62, pp.43-62.  Epub 30-Jan-2021. ISSN 0121-4470.  https://doi.org/10.15446/mo.n62.87185.

Disordered crystalline Fe50Mn25+xSn25-x alloys, with x = -1.25, 0.0, 2.5, 5.0, 7.5 (close to the full-Heusler alloys), were arc-melted in a high purity argon atmosphere and the molten pellets were individually sealed in quartz tubes also under argon atmosphere. Subsequently, they were annealed at 1173 K for 4 days, being finally quenched in a bath with cold water. Structural and magnetic properties have systematically been studied using X-ray diffraction, 57Fe, and 119Sn Mössbauer spectroscopies, and magnetization measurements recorded at room temperature. Rietveld refinement of the X-ray diffraction patterns of the annealed samples with x = -1.25 and 0 has revealed the presence of two hexagonal crystallographic phases: (i) a chemically disordered solid solution identified as ε-(Fe/Mn)3Sn (majority fraction) and (ii) the ε-Fe5Sn3 intermetallic compound (minority fraction). For samples with x = 2.5, 5.0, and 7.5, the Rietveld analysis has only indicated the presence of a chemically disordered solid solution identified as ε -(Fe/Mn)3(Sn/Fe/Mn). Although compositions of the Fe50Mn25+xSn25_x alloys are close to that of full-Heusler alloys, none of them has the expected L2 1 structure. The average crystallite sizes, estimated from the Williamson-Hall method, are in the range of 256-62 nm. The average sizes has gradually decreased as the x-content is increased. Mössbauer results have shown localized-type magnetism from Fe non-equivalent sites, and itinerant-like magnetism on 119Sn-probes. Magnetic hysteresis loops, recorded at 300 K for a maximum field of 2200 Oe, have indicated that the remanent and coercive fields have systematically decreased as the x-parameter has increased. Coercive fields are in the range for soft magnets (1-20 Oe).

Palavras-chave : ⁵⁷Fe Mössbauer spectroscopy; ¹¹⁹ Sn Mössbauer spectroscopy; disordered solid solutions; transferred magnetic hyperfine fields; Heusler alloys.

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