Ultrafine Sm2Fe17N3 soft actuators enabling robust operation at elevated temperature

Magnetoactive soft composites comprising hard magnetic particles embedded in elastomer matrices have emerged as a promising platform for programmable soft actuators capable of remote, untethered actuation. Ferromagnetic Nd 2 Fe 14 B particles, characterized by a high maximum energy product and large remanent magnetization, are regarded as a key material for the implementation of active magnetic actuators. However, the relatively low Curie temperature of Nd 2 Fe 14 B leads to thermal instability, resulting in rapid demagnetization under high-temperature conditions and thereby limiting the actuation performance of soft actuators. Herein, we present an ultrafine Sm 2 Fe 17 N 3 particle-based soft actuator that exhibits robust operation even at elevated temperatures. The novel CaO core-shell strategy employed in this study effectively suppresses the overgrowth of the Sm-Fe intermediate phase, enabling the formation of ultrafine Sm 2 Fe 17 N 3 particles. This process can lead to systematically enhanced coercivity ( H ci up to 12.59 kOe), with concomitant improvements in remanent magnetization ( M r ) and maximum energy product ( (BH) max ) relative to the Ca-free condition. Notably, the Sm 2 Fe 17 N 3 particle-programmed soft actuator maintains robust actuation up to 350 °C, whereas Nd 2 Fe 14 B-based counterparts exhibit severe degradation beyond 200 °C. The findings in this work demonstrate that the synthesized Sm 2 Fe 17 N 3 particles effectively overcome the thermal limitations of Nd 2 Fe 14 B magnets, offering a pivotal alternative for next-generation soft robotics operating in harsh thermal conditions.