Effect of milling on the magnetic properties of Al–Mn obtained by mechanical alloying

Al–Mn powders were prepared to obtain the compound Mn42Al58 by mechanical alloying. The powders were milled during different periods (1 h, 5 h, 11.5 h, 15 h, 20 h and 50 h) using a SPEX 8000 mixer mill in nitrogen atmosphere. The materials were characterized by X-ray diffraction (XRD) and magnetic properties at room temperature, using a vibrating sample magnetometer (VSM). XRD shows partial transformation to α-Mn after only 1 h of milling and a mixture of α-Mn and β-Mn after 11.5 h of milling and further milling resulted in transformation to β-Mn phase with a grain size of 6 nm after 50 h. The change in magnetic properties with milling time is quite dramatic, from a ferromagnetic behavior for α-Mn(Al) to paramagnetic after 11.5 h of milling and showing again ferromagnetic behavior, with a strong increase of magnetization values of 5.5 emu/g, after 50 h of milling with formation of β-Mn(Al).

► Al–42 at.% Mn transforms to α-Mn(Al) by mechanical milling after 5 h of milling.
► Transformation to nano β-Mn is reached after 50 h of milling with 6 nm grain size.
► Milling strongly affects magnetic behavior.