Effects of Co-doping on the crystallization and magnetic properties of Cu-free nanocrystalline Fe-Nb-B alloys

When Fe atoms in Fe-Nb-B amorphous alloy are partially substituted by Co atoms, a decrease of thermal stability of the alloy is investigated. The primary crystallization temperature decreases with the increase of the content of Cobalt. The activation energy of Co-doped Fe-Nb-B alloy is lowered, too. Magnetic measurements show that, both the specific saturation of magnetization and the coercivity of Co-doped Fe-Nb-B nanocrystalline alloys are increased. The increase of specific saturation of magnetization can be attributed to the forming of nano-sized α-FeCo grains, while the increase of coercivity is due to both the higher magnetic crystalline anisotropy of Cobalt atoms and the enhanced pinning effect to the domain walls resulting from the residual of Cobalt atoms on the interface of the α-FeCo grains and amorphous matrix.