Magnetic and Structural Properties of Mechanically Alloyed FexMn0.70?xAl0.30 (x = 0.40 and 0.45) Alloys

Abstract

Alloys of the system Fe x Mn 0.70-x Al 0.30 , x = 0.40 and 0.45, prepared by mechanical alloying during 24, 48, 72 and 84 hours, were studied by X-ray diffraction, Mossbauer spectroscopy and ac magnetic susceptibility. The alloys with x = 0.45 have a bcc structure for all the milling times whereas those with x = 0.40 are bcc for 24 and 48 hours and bcc + fcc for 72 and 84 hours. Mossbauer spectroscopy at room temperature shows that the alloys with x = 0.40 are paramagnetic for all the milling times and their spectra were fitted with a doublet (bcc) for times of 24 and 48 hours and with a singlet (fcc) + a doublet in the other cases. For the x = 0.40 samples, by ac magnetic susceptibility measurements a reentrant spin-glass to ferromagnetic transition (RSG-F) was detected at low temperatures and a ferromagnetic to paramagnetic (F-P) transition at higher temperatures, whereas for the samples with x = 0.45 only a superparamagnetic-like blocking process to ferromagnetic transition (SPM-F) was detected. Moreover, for both compositions, the ferromagnetic phase increases its stability with the milling time due to the increasing disorder induced by milling. The presence of the RSG phase is a consequence of the disorder and the competitive interactions, and presence of the SPM-like blocking process is due to the disorder and the increase of Fe content.