Structural and hyperfine evolution of the (Fe 79Mn 21) 1− xCu x system under milling time

Abstract

The evolution with milling time ( t m) of the structural and hyperfine properties of mechanically alloyed (Fe 79Mn 21) 0.85Cu 0.15 and (Fe 79Mn 21) 0.70Cu 0.30 nominal composition samples are reported. The samples milled during t m = 1, 3, 6, 9, 12, 15 and 18 h are characterized by X-ray diffraction (XRD) and Mössbauer spectroscopy. From the XRD results two phases are observed, a BCC one corresponding to α-Fe(Mn, Cu) and a FCC-phase associated to Fe–Mn–Cu solid solution. Mössbauer spectra show complex structure evidencing several Fe environments. Two hyperfine magnetic field distributions were used to reproduce the spectra, a high magnetic field interaction ascribed to the BCC phase and a low hyperfine magnetic field distribution linked to the FCC solid solution. An increment in the average hyperfine magnetic field ( B hf) and in the isomer shift ( δ) values of the low hyperfine magnetic field distribution is observed when the milling time increases. All the structural and hyperfine parameters remain without changes after 9 h of milling. Once this stationary regime is archived, the B hf of the (Fe 79Mn 21) 0.85Cu 0.15 sample resulted higher than that of the (Fe 79Mn 21) 0.70Cu 0.30 one.