Sn doping-induced nanostructure refinement and magnetic softening in high- <i>B</i> _s Fe-Si-B-Cu nanocrystalline alloys

Minor Sn doping into Fe81.5Si4B13Cu1.5 promotes Cu clustering around Sn atoms in melt-spun amorphous matrix, which in turn induces a high number-density (Nd) of pre-existing α-Fe nanograins averaging 6.0 nm in size. The Sn-tailored precursor structure enables strong competitive growth among the high-Nd α-Fe nuclei/nanograins during conventional annealing, achieving refined nanostructure and improved magnetic softness, while maintaining high saturation magnetic flux density. The 0.1 at.% Sn-doped nanocrystalline alloy with an average grain size of 18.4 nm exhibits low coercivity of 7.7 A/m and high permeability of 10500 at 1 kHz, outperforming the Sn-free alloy (49.1 nm, 213.6 A/m, and 550).