ABSTRACT
The ratios of Fe/Co and Fe/B in a ferromagnetic alloy system, Fe(87-x-y) Co(x) Ti7 Zr6 By (x = 20, 30, and 40 at% and y = 2 and 4 at%), which was produced by the melt-spinning technique in the form of thin ribbons, were investigated to improve the saturation magnetization. The thermal properties T(x) were in the range of 792.0 K to 838.0 K, and it decreased by decreasing Fe/Co ratio. In the as-spun amorphous ribbons, the saturation magnetization and coercivity ranged from 137.5 emu/g to 164.2 emu/g and from 0.027 Oe to 1.245 Oe, respectively. The optimum Fe/Co ratio for the Fe(83-x) Co(x) Ti7 Zr6 B4 system was determined to be 64:36. In other words, the optimum system was Fe60 Co25 Ti7 Zr6 B2, which exhibited robust soft magnetic properties, such as a low coercivity of 0.252 Oe, and high saturation magnetization of 164.2 emu/g (1.55 T). Also, in this system, magnetic properties such as the saturation magnetization and coercivity increased with decreasing Fe/Co ratio.
ABSTRACT
High-performance magnetic materials have immense industrial and scientific importance in wide-ranging electronic, electromechanical, and medical device technologies. Metallic glasses with a fully amorphous structure are particularly suited for advanced soft-magnetic applications. However, fundamental scientific understanding is lacking for the spin-exchange interaction between metal and metalloid atoms, which typically constitute a metallic glass. Using an integrated experimental and molecular dynamics approach, we demonstrate the mechanism of electron interaction between transition metals and metalloids. Spin-exchange interactions were investigated for a Fe-Co metallic glass system of composition [(Co1-x Fe x )0.75B0.2Si0.05]96Cr4. The saturation magnetization increased with higher Fe concentration, but the trend significantly deviated from simple rule of mixtures. Ab initio molecular dynamics simulation was used to identify the ferromagnetic/anti-ferromagnetic interaction between the transition metals and metalloids. The overlapping band-structure and density of states represent 'Stoner type' magnetization for the amorphous alloys in contrast to 'Heisenberg type' in crystalline iron. The enhancement of magnetization by increasing iron was attributed to the interaction between Fe 3d and B 2p bands, which was further validated by valence-band study.
