Enhancement of soft magnetic properties of FeSiBCuNb nanocrystalline soft magnetic composite by SiO₂/FexOy double insulation layers and nanophase structure control

Soft magnetic composites (SMCs) have attracted significant attention as key magnetic materials with the ongoing trend toward high-frequency operation in electronic devices. However, conventional approaches to tailoring the magnetic properties of SMCs rely excessively on coating processes, highlighting an urgent need to develop new control strategies. In this work, the influences of silicone resin content and annealing temperature on the microstructure and soft magnetic properties of FeSiBCuNb nanocrystalline soft magnetic composites (NSMCs) were systematically investigated. During annealing, the thermal decomposition of silicone resin generates a SiO 2 insulating layer. Concurrently, part of the oxygen released from the decomposition of both the silicone resin and zinc stearate reacts with Fe in the FeSiBCuNb powder to form a uniform Fe x O y insulating layer, while the remaining oxygen reacts with Si to generate SiO 2- y . The dual-layer SiO 2 /Fe x O y insulating structure effectively suppresses magnetic losses. Moreover, annealing induces the precipitation of the α-Fe(Si) phase from the amorphous matrix, and the volume fraction and size of the α-Fe(Si) phase increase with increasing the annealing temperature, whereas excessive grain coarsening leads to the deterioration of magnetic properties. The NSMC with a silicone resin content of 1.5 wt% annealed at 450 °C gets remarkable comprehensive magnetic properties with a high effective permeability ( μₑ ) of 37.76, excellent frequency stability up to 1 MHz, and a DC bias performance of 51.82 % at 100 Oe. This work provides valuable insights for the development and application of novel high-performance SMCs by optimizing the coating process and tailoring the nanocrystalline structure.