Investigations on the Surface Crystallization Behavior and Magnetic Properties of Fe_81.5+xSi₃B_10−xP_3.5C_0.2Cu_0.8Nb₁ Soft Magnetic Nanocrystalline Alloys

In this work, the surface crystallization behavior and magnetic properties of Fe_81.5+xSi₃B_10−xP_3.5C_0.2Cu_0.8Nb₁ nanocrystalline alloys were systematically investigated. It was found that the surface crystallization phenomenon occurs at the free-side surface of the as-cast ribbon, and the temperature interval between the first and second crystallization peaks increased to 159 °C with an increase in Fe content up to 83.5 at.%. It is of importance that the structure inhomogeneity caused by the surface crystallization disappears, and a fine and uniform nanocrystalline structure with average grain size of 18 nm is obtained when annealed at 530 °C for 10 min. The presence of an appropriate surface nanocrystallization layer was found to be advantageous in enhancing the soft magnetic properties of Fe_81.5+xSi₃B_10−xP_3.5C_0.2Cu_0.8Nb₁ nanocrystalline alloy, rather than causing their deterioration after annealing. As a result, Fe_83.5Si₃B₈P_3.5C_0.2Cu_0.8Nb₁ alloy ribbons in the optimal annealing state show improved soft magnetic properties, including high B_s of 1.68 T and low H_c of 6.43 A/m. These findings are helpful to understand the influencing mechanism of surface crystallization of amorphous precursor on the crystallization behavior and soft magnetic properties.