Structural and magnetic properties of Fe-Ni mechanosynthesized alloys

Fe100-xNix samples with x = 22.5, 30.0 and 40.0 at.% Ni were prepared by mechanical alloying (MA) with milling times of 10, 24, 48 and 72 h, a ball mass to powder mass (BM/PM) ratio of 20:1 and rotation velocity of 280 rev/min. Then the samples were sintered at 1,000 deg. C and characterized by X-ray diffraction (XRD) and transmission Moessbauer spectrometry (TMS). From the refinement of the X ray patterns we found in this composition range two crystalline phases, one body centered cubic (BCC), one face centered cubic (FCC) and some samples show FeO and Fe3O4 phases. The obtained grain size of the samples shows their nanostructured character. Moessbauer spectra were fitted using a model with two hyperfine magnetic field distributions (HMFDs), and a narrow singlet. One hyperfine field distribution corresponds to the ferromagnetic BCC grains, the other to the ferromagnetic FCC grains (Taenite), and the narrow singlet to the paramagnetic FCC grains (antitaenite). Some samples shows a paramagnetic doublet which corresponds to FeO and two sextets corresponding to the ferrimagnetic Fe3O4 phase. In this fit model we used a texture correction in order to take into account the interaction between the particles with flake shape and the Moessbauer γ-rays.