Structural and magnetic properties of Fe_0.45Mn_0.25Al_0.30 alloys prepared by mechanical alloying

Abstract

Samples from the Fe 0.45 Mn 0.25 Al 0.30 system were prepared by mechanical alloying during 4,8,12,16,22 and 24 h by using two different powder-mass-to-ball-mass ratios of: 1 : 7.5 and 1 : 4. X-ray diffraction (XRD) characterization reveled that samples with 1 : 7.5 ratios consolidate in a ternary Fe -Mn -Al α-Fe solid solution at 8 h (chemical mixing time) and those with 1 : 4 ratios after more than 12 h milling. Möss-bauer effect studies (MS) in conjunction with XRD studies show, in samples with a 1 : 7.5 ratio, a paramagnetic site and a hyperfine field distribution (HFD) for 4 h and only a paramagnetic site for 8 h or more. Therefore, the solid solution is paramagnetic in the stable state. Similar results were obtained for 1 : 4 ratios, but the paramagnetic site was observed after 16 h or more. Mössbauer studies at low temperatures of the sample milled for 12 h and a 1 : 4 ratio demonstrate that this sample presents a re-entrant spinglass to the ferromagnetic transition (RSG -F) at T k = 45 K. This RSG -F transition was proven by an ac magnetic susceptibility measurement, appearing at T = 30 K.