Effects of metalloids in Fe-rich soft magnetic amorphous alloys on magnetization

A large amount of research efforts have been focused on the development of Fe-based amorphous alloys, a kind of soft magnetic materials that is promising in the potential application of motors, transformers and choke coils due to their excellent soft magnetic property. The extraordinarily low coercivity is caused by the disordered structure and the lack of micro-scale anisotropy. Generally, the inclusion of the minor alloying elements necessary for the formation of the amorphous structure can interfere with the Fe-Fe ferromagnetic exchange and reduce the maximum magnetization [1], which is a disadvantage for the efficiency and minimization of the produced devices. On the other hand, it is reported that some common alloying metalloids, such as B and P, can promote the Fe atoms in amorphous alloys into high spin state with larger magnetic moment [2]. The present study is to clarify and optimize the magnetic effect of the alloying elements in Fe-rich amorphous alloys. In this research work, ab initio molecular dynamics simulations were performed for Fe₈₅Si₂B₈P-₄Cu₁, Fe₇₆Si₉B₁₀P₅ and Fe_73.5Si_13.5B₉Nb₃Cu₁ amorphous alloys. Considering the electric charge transfer, electron structure as well as the cluster formation, it is clarified that minor inclusion of B and P can effectively absorb electrons from Fe atoms, making the radii of 3d orbitals of Fe decrease towards optimum ferromagnetic exchange between Fe-Fe atoms. However, with increasing B/P content, the replacement of Fe-Fe bonds by Fe-metalloids bonds makes severe magnetically inert p-d hybridization which reduces the spin polarization of 3d electrons as well as the magnetic moments [3]. Therefore, B and P have complicated magnetic effect in Fe-based amorphous alloys, which appears to promote magnetization with low concentration, but reduces it at larger concentrat- on. Besides, it was found that Si shows no beneficial effect on increasing the magnetization of the amorphous alloys due to the hybridization between Si 3p and Fe 3d orbitals, although experimental data indicate that Si is good for amorphous formation or crystallization controllability [4].