Exchange-Coupling Interaction in Zero- and One-Dimensional Sm₂Co₁₇/FeCo Core-Shell Nanomagnets

Rare-earth-based core-shell spring nanomagnets have been intensively studied in the permanent magnet industry. However, the inherent agglomeration characteristics of zero-dimensional (0-D) magnetic nanoparticles are an issue in practical fabrication of magnetic nanocomposites due to deterioration in exchange-coupling interactions, resulting in inferior magnetic performance. Here, with an aim to overcome the structural limitations, we report a new type of SmCo/FeCo core-shell nanomagnet with a well-dispersed one-dimensional (1-D) structure prepared by a combination of electrospinning and electroless plating processes. An FeCo layer with a tailored thickness on nanoscale SmCo was produced to achieve a sufficient exchange-coupling effect. The influence of electroless plating time on the microstructure of fibers was discussed, and comparisons were made as a function of the magnet shape. A 1-D SmCo/FeCo spring nanomagnet having a core diameter ranging from 150 to 200 nm and a shell thickness of 15-20 nm showed a potent exchange-coupling effect compared with its 0-D counterpart. This effectively reduced self-aggregation and further showed a remarkable enhancement in (BH)_max (above 45.7%). We think that this novel structure marks a new era in the exchange-spring magnet industry and may overcome the limitations of traditional core-shell nanomagnets.