Influence of coating process on the magnetic properties of cold-sintered CoFeSiB@BaTiO3 fibres based soft magnetic composites

Abstract

This manuscript reports a successful preparation of cold-sintered soft magnetic composites based on amorphous Co68.18Fe4.32Si12.5B15 at.% fibres coated with BaTiO3. The coating was achieved through two techniques hydrothermal and thermal evaporation. The amorphous fibres were characterised via X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and in-situ high temperature X-ray diffraction (HT-XRD). A new technique for the preparation of the fibres based soft magnetic composite is proposed consisting in wounding the fibres on a Teflon support and the application of a cold sintering process in an autoclave. The DC magnetic characterization of the composite compacts revealed that the compact based on fibres coated via the thermal evaporation coating technique exhibits superior magnetic properties (Bs = 0.4 T, Hc = 1.85 A/m, μrmax = 49500) compared to the compact based on fibres coated via the hydrothermal method (Bs = 0.34 T, Hc = 2.31 A/m, μrmax = 39200). The AC magnetic characterisation of the compacts showed that the magnetic relative permeability of both compacts is constant over the entire tested frequency range tested (50 Hz–10 kHz). The value of the magnetic relative permeability of the composite based on fibres coated via the thermal evaporation technique is around 1650 while for the compact based on hydrothermally coated fibres a value of only 850 was obtained. The total losses were also evaluated, the composite based on thermal evaporation-coated fibres exhibiting the lowest losses of 3.11 W/kg at the frequency of 10 kHz and induction of 0.1 T. The loss separation analysis highlighted that the main type of losses, especially at high frequency, depends on the technique used for the coating of the fibres.