Magnetic phase diagram of the Fe_xMn_0.60-xAl_0.40 (0.20≤x≤0.60) alloys mechanically alloyed for 48 hours

Alloys of the system Fe_xMn_0.60-xAl_0.40, 0.20 ≤ x ≤ 0.60, were prepared by mechanical alloying for 48 hours. The Mössbauer spectra were fitted with either a single line and a quadrupolar doublet or a single line, a quadrupolar doublet and a hyperfine field distribution (HFD), according to their hyperfine structures. Alloys with x ≤ 0.40 show a paramagnetic character at RT while those with x ≥ 0.45 are ferromagnetic with some paramagnetic sites due to the disorder. At 77 K, one can distinguish three types of alloys which display different magnetic behaviors: (i) antiferromagnetic with lower Fe concentration, (ii) paramagnetic with intermediate Fe contents and (iii) ferromagnetic with high Fe content. In the 0.40 ≤ x ≤ 0.60 composition region of the ac magnetic susceptibility X vs. T, superparamagnetic clusters appear inside the ferromagnetic matrix, as a consequence of the high Fe content and the disordered character of the samples.