Study On Phase Evolution And Magnetic Properties Of 2:17 Type Sm Co Permanent Magnets

The 2:17 type SmCo permanent magnets are well known for their advanced magnetic properties and excellent thermal stability,which are widely applied in the aerospace and defense industry.The typical cellular microstructure of 2:17 type SmCo permanent magnet is critical to its magnetic performances,which forms by the precipitation enhancement during the series of heat treatment processes.As for the mechanism of the phase transformation during aging heat treatment,it is not very clear.In this paper,Dy is doping into the 2:17 type SmCo permanent magnet for stabilizing the related phase transitions and the investigation on the formation of the symmetric nanocrystalline,which are supposed to be the original 2:17R phase.Those phases play an important role in 2:17R phase ordering from the short-range to the long-range.Comparing to the 2:17 type SmCo permanent magnet,the 2:17R disordered nanocrystalline of symmetric structure is retained in the 2:17 type(Sm,Dy)Co permanent magnet.Phase structures and magnetic performance of 2:17 type SmCo and(Sm,Dy)Co permanent magnets have been studied by X-Ray Diffraction,Transmission Electron Microscope,Physical Property Measurement System and Superconducting Quantum Interference Device(XRD/TEM/PPMS/SQUID),respectively.Considering the identification of the phase structures and the measurement of the magnetic performance of 2:17 type SmCo and(Sm,Dy)Co permanent magnets,we propose an assumption to clarify the mechanism of the phase transformation during aging of 2:17 type SmCo permanent magnet.Besides,a simplified atomic model of the formation of 2:17R symmetric nanocrystalline has been given in this paper as well.Based on the mechanism of the phase transformation during aging of 2:17 type SmCo permanent magnet,the relationship between heat treatments and magnetic properties involving in the formation of cellular microstructure of 2:17 type(Sm,Dy)Co permanent magnet,has been investigated in this study.The heat treatments of isothermal aging and slow cooling have been adjusted to obtain better ordered microstructure.As for the phenomenon of abnormal coercivity in 2:17 type(Sm,Dy)Co permanent magnets,it was discussed according to the theory of spin-reorientation-transition and well explained.