Spin-exchange interaction between transition metals and metalloids in soft-ferromagnetic metallic glasses

High performance magnetic materials are of immense industrial and scientific importance in wide ranging electronic, electromechanical, and medical device technologies. Metallic glasses, with fully amorphous structure, are particularly suited for advanced soft-magnetic applications due to their homogeneous and isotropic structure down to the atomic scale. However, fundamental scientific understanding of spin-exchange interaction between the metal and metalloid atoms (that typically constitute a metallic glass) and the resulting desirable magnetic behavior is lacking. Using an integrated experimental and molecular dynamic approach, we demonstrate the mechanism of electron interaction between transition metals and metalloids which results in the enhanced magnetic properties of amorphous metallic alloys. Spin-exchange interactions were investigated for a Fe-Co metallic glass system of composition [(Co_1−xFe_x)_0.75B_0.2Si_0.05]₉₆Cr₄. The saturation magnetization was found to increase with increasing Fe concentration. 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.

Recent research on engineered magnetic materials is primarily driven by cutting-edge technologies in magnetic storage, electro-magnetic shielding, magnetic flux-gate sensors, magnetic switches, micro-electromechanical systems (MEMS), and medical devices. Amorphous metals are particularly of interest in this regard due to their grain boundary-free isotropic structure, which results in exceptional magnetic properties. This paper deals with the issue with a good back-up of DFT calculations.

J. Phys. – Cond. Matter, Vol. 28 (2016) 216003 (9 pages)