Mössbauer spectroscopy and X-ray diffraction study of Fe x Mn 0:70−x Al 0:30 (0:40 < x < 0:70) alloys prepared by mechanical alloying

Abstract

In order to study the structural and magnetic behaviour of FexMn0.70−xAl0.30 (0.40≤x≤0.70) alloys prepared by mechanical alloying, Mossbauer spectroscopy and X‐ray diffraction techniques have been employed. All the alloys were prepared in 24 h and, in addition, for x=0.45 milling times of 4, 8, 12, 16 and 24 h were considered. X‐ray diffraction showed that all samples exhibit bcc‐type reflections. A slight decrease in grain size and a slight increase in lattice parameter with increasing Mn content were observed. For x=0.45, an increase in grain size with milling time has been evidenced. For this composition and 4 h of milling, the more intensive peak (1 1 0) was fitted with three peaks corresponding to that of Mn, Fe and the alloy, respectively. For 12 h milling only bcc peaks of the alloy were obtained. As the Fe concentration was increased beyond x=0.50, a phase change from paramagnetic to ferromagnetic, as well as an increment in the mean hyperfine field with x, was detected. For x=0.45 and 4 h of milling we registered the presence of both a single line, corresponding to the alloy, and a hyperfine field distribution with peaks in 27.5 and 23 T, as well as peaks at lesser fields. These peaks are associated to Fe sites with two or more Al and/or Mn atoms as next neighbours. These results are in agreement with those obtained by X‐ray diffraction.