Influence of mechanical milling on the physical properties of SmCo_5/Fe_(65)Co35 type hard/soft magnetic nanocomposite

摘要

The influence of milling type on the structural and magnetic behaviour of mechanically milled SmCo5/ Fe_(65)Co_(35) has been studied. By adjusting the mill speed parameters, {Ω/ω), three types of milling have been performed: shock mode process (SMP), friction mode process (FMP) and a combined shock followed by a friction mode process. It was found that in SMP conditions the remanent magnetization and composite coercivity increase with increasing milling time. The best exchange coupling, with a coercivity of 1.05 T, was obtained for samples milled for 8 h in SMP and annealed for 2 h at 550 °C. On the other hand, the low energy of FMP does not succeed in producing a microstructure adapted to favour the inter-phase exchange interactions between the soft and hard magnetic phases. A combined milling process does not change significantly the microstructure obtained previously after 8 h of SMP. This indicates that the microstructure of the composite is formed primarily during SMP while FMP, less energetic, does not drastically affect the crystallite size and crystallite shape of SMP samples. X-ray diffraction patterns were used to follow the evolution of the structure and microstructure. The diffusion of Fe and Co from Fe_(65)Co_(35) to SmCo_5 phase leads to the formation of Sm_2(Co,Fe)_(17)/Fe-Co composite. The magnetic behaviour was checked from hysteresis curves and dM/dH vs. H plots.