“Fe-Ni soft magnetic nanocrystalline materials developer by mechanical alloying”

P. MENDOZA ZÉLIS; CLAUDIA E. RODRÍGUEZ TORRES; .F. CABRERA; M. FERNÁNDEZ VAN RAAP; G.A. PASQUEVICH; F.H. SÁNCHEZ; M. HIDALGO; A. GONZÁLEZ; LL. ESCONADA; J.J. SUÑOL

Barcelona (Spain)

Workshop; 2nd NanoSpain Workshop; 2005

Magnetic nanocrystals embedded in magnetic and non-magnetic amorphous matrices are of great interest to develop softer and better magnetic materials for technological use for the manufacturing of dense dispersion of nanocrystals with high saturation magnetization and high permeability [1]. In this work, we present the magnetic, structural and thermal analysis of several Fe-Ni based alloys obtained from the elemental powders in a high-energy mechanical alloying device. Ball milling provides a non-equilibrium route to obtain nanocrystalline materials from elemental powders. The formation of the nanocrystalline structure during mechanical alloying was followed by X-ray diffraction and high-resolution transmission electron microscopy. Depending on the milling conditions, different nanocrystalline size and distribution was obtained. As an example, figure 1 shows the evolution of the crystalline size of a Fe-Ni based alloy versus the milling velocity. Furthermore, the partial substitution of Fe by Ni favours the diminution of the crystalline size. The thermal evolution of the samples was analyzed with differential scanning calorimetry. There is a broad hump in the temperature ranges of 300-600 K. The humps are associated with the relief of internal stresses, since no phase transformations were detected in X-ray diffraction and Mössbauer studies performed in alloys with similar composition [2,3]. The exothermic peak over 600 K is related to the crystalline growth of the á-Fe phase. Thermal treatments at specific temperatures were performed to analyze and compare the structure evolution and thermal stability of the different alloys. Figure 2 shows the Mössbauer spectra evolution of a Fe-Ni-Nb based alloy. This magnetic materials were analyzed by performing the hysteresis loop at room temperature. The results allow us to state that mechanical alloying is a process capable to obtain soft magnetic materials. As expected, the more nanocrystalline alloy presents a best soft behavior. Magnetic susceptibility measurements at low temperature are under study. The contamination increases with the milling time. Nevertheless, the results show only slight (< 1.0 at.%) contamination from the milling tools (Fe, Ni and Cr) as well as oxygen presence (2.5 ± 0.8 at.%) after 80 hours of milling.