Mossbauer spectroscopy and X-ray diffraction study of FexMn0.70-xAl0.30 (0.40 < x < 0.70) alloys prepared by mechanical alloying

In order to study the structural and magnetic behaviour of FexMn0.70-xAl0.3 0 (0.40 less than or equal tox less than or equal to0.70) alloys prepared b y mechanical alloying, Mossbauer spectroscopy and X-ray diffraction techniq ues have been employed. All the alloys were prepared in 24 h and, in additi on, for x=0.45 milling times of 4, 8, 12, 16 and 24 h were considered. X-ra y diffraction showed that all samples exhibit bcc-type reflections. A sligh t decrease in grain size and a slight increase in lattice parameter with in creasing Mn content were observed. For x=0.45, an increase in grain size wi th 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 p eaks of the alloy were obtained. As the Fe concentration was increased beyo nd 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, correspon ding to the alloy, and a hyperfine field distribution with peaks in 27.5 an d 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 result s are in agreement with those obtained by X-ray diffraction.