Phase transformation in nanocrystalline Sm2Co17permanent magnet material
Single-phase ultrafine nanocrystalline Sm2Co17, a candidate material for permanent magnets, was prepared by a novel simple route based on a home-built `oxygen-free'in situfabrication system. The as-prepared nanocrystalline Sm2Co17has the stable hexagonal Th2Ni17-type (2:17 H) crystal structure at room temperature, which is distinctly different from the conventional polycrystalline Sm2Co17having the rhombohedral Th2Zn17-type (2:17 R) crystal structure at room temperature. Phase transformations in the nanocrystalline Sm2Co17alloy were investigated systematically by a series of annealing experiments. It was found that, along with the nanograin growth in the heat-treatment process, the crystal structure of the room-temperature phase transforms from 2:17 H to 2:17 R. The magnetization behavior of Sm2Co17alloys in different structural states was characterized. The relationship between the magnetic performance and the structure characteristics was analyzed. Understanding the phase transformation of Sm2Co17nanocrystals facilitates the development of nanocrystalline Sm2Co17-type magnets for high-temperature applications.