Characterization of magnetic phases in the FexMn0.65−xAl0.35 disordered alloys

Melted alloys of the FexMn0.65−xAl0.35 disordered system, 0.25⩽x⩽0.65, were experimentally studied by Mössbauer spectrometry, vibrating sample magnetometry and AC magnetic susceptibility. All the alloys exhibit the BCC structure with a nearly constant lattice parameter (2.92 Å). Mössbauer studies at room temperature (RT) show that in the 0.25 ⩽x⩽0.45 range the alloys are paramagnetic (P) while in the 0.50⩽x⩽0.65 range, they are ferromagnetic. At 77 K, Mössbauer studies show that the alloy with x=0.25x=0.25 presents weak magnetic character that is consistent with an antiferromagnetic (AF) behavior due to the high Mn content, while those with 0.30⩽x⩽0.40 are paramagnetic, and those in the 0.45⩽x  ⩽0.65 range are ferromagnetic (F) with a mean field increasing with the Fe content. Hysteresis cycles at RT prove the paramagnetic character of the alloys between x=0.25x=0.25 and 0.40 and the ferromagnetic character for x⩾0.45x⩾0.45. Complementary measurements using AC magnetic susceptibility permit a magnetic phase diagram to be proposed, with the P phase for high temperature and all the compositions, the AF phase for low Fe content and at low temperature, the F phase for high Fe content above RT and the spin glass phase for all the compositions and at temperatures lower than 46 K. In addition, the mean field renormalization group (MFRG) method, applied to a random competitive and site dilute Ising model with nearest-neighbor, gives rise to magnetic phase diagram, which fairly agrees with previous experimental one.