Journal of Materials Research and Technology (Jan 2024)
Effects of adding carbonyl Fe or Mn–Zn ferrite powders to fibre-based soft magnetic composites prepared via hybrid cold sintering/spark plasma sintering
Abstract
This manuscript presents the preparation and characterisation of fibres-based soft magnetic composites that incorporates a secondary magnetic phase such as carbonyl Fe and Mn–Zn ferrite nanopowder. Amorphous Fe77.7Si7.5B15 at.% fibres were coated with a dielectric layer of ZnO via thermal evaporation. SEM-EDX investigations revealed that the thermal evaporation technique leads to a complete coating of the fibres with a ZnO coating having a thickness of 150–250 nm as demonstrated via STEM-EDX analysis. The hybrid cold sintering/spark plasma sintering technique was used for the first time for the preparation of soft magnetic composites. Substituting 10 wt% of ZnO with carbonyl Fe resulted in an increase in the saturation magnetisation of the composite from 0.61 T to 0.7 T. In contrast, substituting it with Mn–Zn ferrite led to a decrease in saturation magnetisation from 0.61 T to 0.5 T. The coercivity of the composites increased when ZnO was partially substituted with Fe or Mn–Zn ferrite, rising from 16.9 A/m to 22.7 A/m and 36.8 A/m, respectively. AC magnetic characterization revealed that the relative permeability of the composites remains constant across the entire frequency range tested for all composites. However, the introduction of carbonyl Fe or Mn–Zn ferrite led to a reduction in the relative permeability values of the composites from 1310 to 1200 and 890, respectively. The core losses of the composites were also influenced by the secondary magnetic phase used. The use of Mn–Zn ferrite or carbonyl Fe resulted in a significant increase in the hysteresis losses of the composites. When carbonyl Fe was used for partial substitution of ZnO, a substantial increase of the eddy currents losses of the composites was noted.
