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Mechanical alloying method was applied to prepare nanocrystalline Co40Fe40Ni20, Co50Fe40Ni10, Co52Fe26Ni22 and Co65Fe23Ni12 alloys. X-ray diffraction, Mössbauer spectroscopy and magnetization measurements were used as complementary methods to obtain structural data and to determine magnetic properties of the as-milled as well as the thermally treated samples. X-ray diffraction proved that during mechanical alloying process the Co–Fe–based solid solution with BCC lattice was formed in the case of Co40Fe40Ni20 and Co50Fe40Ni10, while for Co52Fe26Ni22 and Co65Fe23Ni12 systems the Co–Ni–based solid solutions with FCC lattice were obtained. Mössbauer spectroscopy revealed hyperfine magnetic field distributions, which reflect the different surroundings of 57Fe isotopes by Co, Fe and Ni atoms, depending on the chemical composition of the alloy. The most probable atomic configurations were determined on the basis of the local environment model. Thermal treatment of the mechanosynthesized alloys led in some cases to decomposition of the suitable solid solution into the mixture of two solid solutions. In other cases, the phase composition of the alloys was stable or the type of the crystalline lattice was changed during annealing. Moreover, thermal treatment led to an increase in the grain size and a decrease in the level of internal strains that influenced the magnitudes of the effective magnetic moments and Curie temperatures of the investigated alloys.
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