Owing to high Saturation Magnetization (M_s) and high Remanence Magnetization (M_r), Rare Earth (RE) based Permanent Magnet (PM) has been widely used in various applications such as motor in Electric Vehicle (EV) and generator. With increasing concerns about climate change, EV is considered as a next generation vehicle because EV did not emit pollutants such as CO₂, NO_x and SO_x. Over the past years, Nd₂Fe₁₄B is mainly used as PM in EV due to excellent maximum energy product (BH_max) around room temperature. However, The Nd₂Fe₁₄B has relatively low operating temperature (<200℃), which limits high speed operation. On the other hand, SmCo₅ possesses high thermal, chemical stability and coercivity (H_c), making it a suitable magnetic material for high speed operation in harsh environment. However, unfortunately SmCo₅ PM was only used in limited areas due to the lower M_s, M_r, BH_max than Nd₂Fe₁₄B. Therefore, interest in research to improve magnetic properties of SmCo₅ is increasing. In particular, exchange coupling in core/shell structure between hard magnetic core and soft magnetic shell has attracted much attention because it can increase M_s, M_r, BH_max simultaneously while reducing high price RE element. In our work, we utilized electroless deposition on SmCo₅ Nanoparticles (NPs) to fabricate exchange coupled SmCo₅/FeCo hard/soft nanocomposites because of low cost and easy to control the soft phase thickness by modulating electrolyte bath parameters such as pH, temperature and additives. However, prior research clarified that the exchange coupling in 0-Dimensional NPs via electroless deposition was difficult because of inevitable particle aggregation caused by magnetic dipoles. Thus, inhibition of particle aggregation would be significant breakthrough. Accordingly, we prevented particle aggregation through ultrasound during the electroless deposition process.

The SmCo₅ NPs were fabricated through Sn-sensitization, Pd-activation, and ultrasound assisted FeCo-electroless deposition, successively. Figure 1 shows that the schematic illustration of the effects of ultrasound. The magnetic properties of SmCo₅/FeCo NPs were measured by Vibrating-Sample Magnetometer (VSM). When ultrasound was not applied, the hard magnetic properties reduced due to agglomerated NPs. On the other hand, in case ultrasound was applied exhibits exchange coupled hysteresis loop. Figure 2 shows that minor hysteresis loops of exchange coupled SmCo₅/FeCo NPs fabricated by ultrasound assisted electroless deposition. We successfully fabricated exchange coupled SmCo₅/FeCo NPs and the M_s, M_r, theoretical BH_max increased about 11%, 10.7%, 24.3%, respectively.

As a result, SmCo₅/FeCo which fabricated by ultrasound assisted electroless deposition showed the increase in magnetic properties while maintaining M_r/M_s, which might broaden the future application fields.