Study On The Structure And Magnetic Properties Of Sm-Co Permanent Magnetic Alloys

Sm-Co permanent magnetic materials behave many excellent magnetic properties,such as high magnetocrystalline anisotropy field,low intrinsic coercivity temperature coefficient and high Curie temperature.Therein SmCo₅ and Sm₂Co₁₇ are the first generation and the second-generation permanent magnet respectively,their structures and properties had been extensively studied.However,SmCo₅ and Sm₂Co₁₇ phases both have various kinds of atomic structures and subtle differences exist in these atomic structures with different Sm:Co atomic ratios.Moreover,different preparation methods also lead to such subtle changes in phase structures.When B element is added to the Sm-Co alloys,some Sm-Co-B alloys get high magnetization,high Curie temperature and high coercivity.Furthermore,the magnetic properties of different Sm-Co-B magnetic alloys are mainly due to the structures of borides.Thus,the atomic fine structure of these alloys in different states were studied by means of the extended X-ray absorption fine structure?EXAFS?.In this paper,the Sm-Co,Sm-Co-B alloys with different states were prepared by vacuum arc furnace,vacuum annealing furnace and vacuum melt-spinning furnace.X-ray diffracmeter,scanning electron microscopy,vibrating sample magnetometer and synchrotron radiation facility were used to study the effects of different preparation methods on crystalline structures and properties of the alloys,and the EXAFS fitting method was used to analyze the fine structure of atoms in each phase of alloys.It was found that the alloys prepared in different processes have different structures or phase contents,different fine structures of atoms and magnetic properties.In addition,there is a small amount of bias between the actual atomic ratios of phases and the theory atomic ratios of phases.For the Sm-Co alloys,annealed SmCo₅ alloy has a higher coercivity?Hc=4546.6 Oe?,which is consisted of 70.10%SmCo5 phase and 29.90%Sm2Co7 phase.The actual atomic ratio of Co:Sm in SmCo₅ phase is about 5.16,the actual atomic ratio of Co:Sm in Sm2Co7 phase is about 3.80.While the as-cast SmCo9.8 alloy behaves a higher saturation magnetization?Ms=174.59 emu/g?,which is consisted of Sm₂Co₁₇ phase and a little Co phase,and the Sm₂Co₁₇ phase is consisted of 59.38%Sm₂Co₁₇ phase with rhombohedral structure and 40.62%Sm₂Co₁₇ phase with hexagonal structure,while the averaged atomic ratio of Co:Sm in Sm₂Co₁₇ phase is about 9.04.For the Sm-Co-B alloys,melt-spinning SmCo₄B alloy has a higher coercivity?Hc=18548 Oe?,which is consisted of 92.58%SmCo₄B phase and 7.42%amorphous phase,the grains of SmCo₄B phase are very small and the amorphous phase is distributed in its grain boundaries.While the as-cast Sm₃Co₂₀B alloy has a higher saturation magnetization?Ms=90.88 emu/g?,which is consisted of 87.89%Sm₃Co₂₀B phase,8.51%SmCo₅ phase and 3.61%Sm₂Co₁₇ phase,the Sm₂Co₁₇ phase and SmCo₅ phase are jointly distributed in near grain boundaries of Sm₃Co₂₀B phase.