Synthesis of spherical and heterogeneous core–shell structure Co@Fe particles and electromagnetic absorption performance investigation

Chemical liquid-phase coating was used to prepare spherical, flower-shaped, and thorny-shaped Co@Fe composite particles with varying mass ratios of Co : Fe. The effects of reaction conditions on the microstructure, morphology, static magnetic properties and electromagnetic wave absorption characteristics were investigated. The Co@Fe composite particles are primarily composed of Co and Fe, maintaining the morphological features of the original Co particles while exhibiting changes in particle size and surface structure. The average particle diameters of spherical Co@Fe particles were measured to be 1.32 μm, 1.59 μm, and 1.62 μm, with the particle surfaces being relatively smooth when the Co : Fe mass ratio was 1 : 1. For flower-shaped Co@Fe particles, the sizes were 1.59 μm, 1.61 μm, and 2.96 μm, with the original sharp, flake-like petals transforming into rounded, globular protrusions. The average diameters of thorny-shaped Co@Fe particles were approximately 6.11 μm, 7.53 μm, and 8.03 μm, where the spear tips became less sharp and the aspect ratio of the spear-like structure increased. The XRD patterns revealed FCC-Co, HCP-Co, and Fe, and as the Fe content in the Co@Fe particles increased, both saturation magnetization and coercivity decreased. The thorny-shaped Co@Fe particle sample achieved the minimum reflection loss of −16.47 dB at a thickness of 1.8 mm, with an effective absorption bandwidth of 4.96 GHz.