The magnetic properties of the nanoparticle powders are strongly dependent on the preparation conditions. The milling process produces damages and defects not only on the surface, but also the crystal structure inside the particles, that cause an undesired strong reduction of saturation magnetization (Ms) and an increase of coercivity (Hc). A suitable post-milling heat treatment is able to heal the particles and recover most of their saturation magnetization and magnetic softness. The nanoparticles are then mixed with paraffin for microwave and radar absorption measurements. | Vietnam Journal of Chemistry, International Edition, 54(6): 704-709, 2016 DOI: High-energy ball milling preparation of and (Co,Ni)Fe2O4 nanoparticles for microwave absorption applications Chu Thi Anh Xuan1,2, Ta Ngoc Bach1, Tran Dang Thanh1, Ngo Thi Hong Le1, Do Hung Manh1, Nguyen Xuan Phuc1, Dao Nguyen Hoai Nam1* 1 Institute of Materials Science, Vietnam Academy of Science and Technology 2 Department of Physics, University of Science, Thai Nguyen University Received 5 August 2016; Accepted for publication 19 December 2016 Abstract Microwave and radar absorbing materials (MAM and RAM) are widely used for reducing electromagnetic interference (EMI) for electronic equipment and devices, in electromagnetic anechoic technique, and especially in radar stealth technology. Ferromagnetic and ferrimagnetic nanoparticles have been known to have a strong microwave absorbing capability. To study magnetic MAMs and RAMs, we have prepared ferromagnetic and several (Co,Ni)Fe2O4 ferrimagnetic nanoparticle powders using high-energy ball milling technique, which is capable of producing nanoparticles in reasonably larger scale comparing to conventional chemical methods. The magnetic properties of the nanoparticle powders are strongly dependent on the preparation conditions. The milling process produces damages and defects not only on the surface, but also the crystal structure inside the particles, that cause an undesired strong reduction of saturation magnetization (Ms) and an increase of coercivity (Hc). A suitable post-milling heat treatment is able to heal the particles and recover most of their saturation magnetization and magnetic softness. The nanoparticles are then mixed with paraffin for microwave and radar absorption measurements. Keywords. Microwave absorbing materials, radar absorbing materials, electromagnetic interference, stealth technology, magnetic nanoparticles. 1. INTRODUCTION As electronic and radio .
