Magnetic and structural behaviours of nanocrystalline Fe70.8Nb3.7Cu1Al2.7Mn0.7Si13.5B7.6 alloy

The crystallization behaviour of Fe70.8Nb3.7Cu1Al2.7Mn0.7Si13.5B7.6 alloy prepared in the form of amorphous ribbons by melt-spinning technique was studied using differential scanning calorimetry and the temperature variation in resistivity. An X-ray diffaction and transmission electron microscopy study showed the formation of alpha-Fe(Si, Al) and/or Fe-3(Si, Al) nanoparticles after the first stage of crystallization. The activation energy for this nanophase formation was 68 kcal mol(-1). The brittleness of the alloy increased with the formation of nanoparticles after heat treatment. Superior soft magnetic properties were achieved when the material was heat treated at 790 K for 15 min. The particle size at the optimum heat treatment condition for superior soft magnetic properties was found to be 6.0 +/- 0.5 nm which was less compared than for the Fe-Nb-Cu-Si-B system. The observed coercivity value at the optimum heat treatment condition was found to be 0.32 A m(-1) (approximately 4 mOe). The presence of A1 in the alloy reduced the particle size and the magnetic anisotropy energy of the system, which resulted in superior soft magnetic properties of the heat-treated materials