Adjusting shell composition and content of Co-based bimetal core-shell microspheres toward the broadband microwave absorption

摘要

To improve the high-frequency absorption and achieve the broadband absorption, the surface modification of Co microspheres by metal (Cu, Ag and Fe) shells was achieved via simple and controllable galvanic replacement and chemical vaporous deposition, respectively. The influences of the shell composition and shell content on the static magnetic and microwave absorption performance were systematically studied. As for the Co/Cu and Co/Ag core-shell microspheres (CSMPs), the saturation magnetization (M-s) decreased and the coercive force (H-c) increased with the increased content of diamagnetic Cu and Ag shell. Co/Fe CSMPs consisting of ferromagnetic core and ferromagnetic shell exhibited better soft magnetic properties. Due to the enhanced exchange resonance and improved impedance matching, coating ferromagnetic Co microspheres with moderate diamagnetic Cu and Ag shell metal can significantly enhance the high-frequency absorption and expand the absorption bandwidth. Hereinto, Co0.9868Ag0.0132 CSMPs exhibited the optimal microwave absorption performance with a strong absorption (- 45.27 dB), a thinner sample (1.65 mm) and broader bandwidths (7.36 GHz for R-L <= -10 GHz; 3.27 GHz for R-L <= -20 GHz). Owing to the excellent microwave absorption and soft magnetic properties, these bimetal CSMPs have great potential in biomedicine, magnetic devices, catalysis, lithium-ion batteries and microwave absorption.