Magnetic and Structural Properties of Fe–Mn–Al Alloys Produced by Mechanical Alloying

摘要

The effects of concentration and preparation conditions on the magnetic and structural properties of samples of the Fe–Mn–Al system prepared by mechanical alloying were studied by M?ssbauer spectroscopy, X-ray diffraction and susceptibility techniques. X-ray diffraction showed that samples with high Al content (40 at.) and prepared with low milling times (lest than 12 hours) present the peaks of Mn, Fe–Al alloy and broad peaks which correspond to the ternary bcc alloy. For 12 hours the Mn peak disappears and for 24 h or more the bcc ternary phase is totally formed. For t ≥ 24 h M?ssbauer spectroscopy studies proved that: samples rich in Fe are ferromagnetic (F) at room temperature (RT) and present a reentrant spin-glass (RSG) behavior for low T; samples with intermediate Fe values are paramagnetic (P) at RT and SG for low T; and those with low Fe content are P at RT, antiferromagnetic (AF) at low T and RSG at very low T. By ac magnetic susceptibility it was possible to detect an additional magnetic phase in the F and P regions which was attributed to a superparamagnetic (SP)-like behavior. XRD and M?ssbauer spectroscopy of samples with low Al content (7.5 at.) showed that they present a fcc AF phase and a Fe–Al F phase for low milling times (≤10 h). For bigger times the only detected phase is the fcc, which is AF for low Fe contents and P for high Fe contents. The effect of using small balls is to enhance the alloyed process.