Iron and molybdenum powder mixture exposed to stepwise mechanical alloying in air and in nitrogen is studied by X-ray diffraction, Mössbauer spectrometry, electron microscopy, magnetic measurements, and differential thermal analysis. The Mössbauer spectra are interpreted in terms of various contributions. The main contribution is associated with the FeMo nanograin core, which is similar to the bcc-FeMo bulk alloy of the same composition, i.e., a ferromagnetic solid solution of Mo in Fe. The increasing milling time contributes to a decrease in grain size. It results in a decrease of the volume fraction of the grain cores and simultaneously to an increase in a volume fraction of other contributions of highly defected surface zones and very close surface layers influenced by the milling atmosphere. The Rietveld interpretation of diffraction patterns, the scanning, and transmission electron microscopy completed by the EDX analysis and magnetic measurements are in good agreement with the Mössbauer spectra interpretation.
Nanostructured material Mechanical alloying Magnetic properties Grain core Defects
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The authors thank M. Hapla and Dr. A. Kroupa for magnetic and DTA measurements and the Czech Science Foundation (P108/11/1350) for financial support.