Structure, magnetic and Mossbauer studies of mechanically alloyed Fe-20 wt.% Ni powders

Fe-20 wt.% Ni alloys were prepared using a planetary ball mill PM 400 from Retsch (with different milling times for Omega = 400 rpm, (0 = 800 rpm) and P4 vario ball mill from Fritsch (with different milling conditions (Omega/w), Omega and omega being the disc and the vial rotation speeds, respectively). The bcc-Fe(Ni) phase formation is identified by X-ray diffraction. The higher the shock power and the higher milling time are, the larger the bcc lattice parameter and the lower the grain size. The highest value of the coercive field is 1420 A/m for Fe-20 wt.% Ni (with shock mode (424 rpm/100 rpm) after 36 h of milling), while the lowest value is 110 A/m for (400 rpm/800 rpm) after 96 h of milling. The milling performed in the friction mode favors the formation of alloys exhibiting a soft magnetic behavior for Fe-20 wt.% Ni alloys. The Mossbauer spectra of the alloys recorded at 77 and at 300 K differ according to the milling conditions and give relevant information on the local structure environment in relation with the nature of the mode used (friction or shock mode). (c) 2005 Elsevier B.V. All rights reserved.