A hard magnetic Sm-Co alloy nanopowder is successfully prepared by the recently-developed low oxygen-induction thermal plasma (LO-ITP) process. Spherical particles with an average diameter of 61 nm are achieved. According to the X-ray diffraction (XRD) profile, hard magnetic compounds of SmCo5 and SmCo7 are obtained. Transmission electron microscopic (TEM) observation confirms that the Sm-Co particles have a uniaxial anisotropic structure. This work also leads to the discovery of a previously-unknown core/shell particle with a Co-core/Sm-Co-shell structure, which has an ideal interface for exchange coupling, as the particle is formed with no oxide phase in the interface between the Co-core and Sm-Co-shell. Magnetic measurements show that coercivity is 5.6 kOe at room temperature and magnetization is 80 emu/g at 9 T, and the recoil curve shows spring-back behavior, suggesting exchange-coupling between the Co-core and the Sm-Co-shell. A numerical analysis demonstrates the formation mechanism of the Sm-Co alloy particles and the core/shell particles, and also suggests a strategy for improving the magnetic properties of the Sm-Co alloy nanopowder.
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