Study On SmCo-Type Binary Nanocrystalline Permanent Magnets

The rare earth permanent magnetic material is an important functional material, which has widespread application in the computer,the network,the correspondence, the aerospace, the office automation,the electrical appliances,the healthcare and the high tech field. Especially in modern industry and the aviation, aerospace and defense field, which pushes the rare earth permanent magnet material more widly used. Meanwhile, to the high magnetism performance and the high application temperature's permanent magnet has more and more intense demand. Although both SmCo₅ and Sm₂Co₁₇ compounds have been researched, yet the structure and magnetization studied was under micron size. However, their structure and magnetism performance will be different with the former research under the nanometer size. So we hope that the high performance nanocrystalline magnet can be obtained through the improvement preparation craft. Moreover, it is difficult to obtain the metastable phase by the traditional preparation way. With further understanding, more and more researchers put their into the research of metastable phase. For example: 1:7 and 1:13 type of SmCo not only has the high coercive force and the saturatio magnetization, moreover, it has the good high temperature stable performance, which has the very considerable prospect in the high temperature permanent magnet material researching field. SmCo₁₃ was forecasted that has the highest magnetocrystalline anisotropy field and the maximumcurie temperature, it will be a big breakthrough in permanent magnet material researching.The Spark Plasma Sintering (SPS) has high sintering stress, low sintering temperature and rapid sintering speed, which has brought the new mentality for the SmCo research. In this study, we plan to make the full dense SmCo bulk nanocrystalline sintered magnet by the new technology, which is used by the technical routes of melt-spinning, mechanical milling and using SPS with the condition of 700℃for 3 min with a pressure of 500 Mpa, the SmCo₅, Sm₂Co₁₇, and SmCo₁₃ nano -crystalline magnets were obtained. We make a systemic study on the sintered magnet.The crystal structures and the grain size of the SmCo₅, Sm₂Co₁₇ and SmCo₁₃ bulk magnets were measured by mean of powder x-ray diffraction (XRD) with Cu-Kαradiation. Microstructure was detected by TEM and the magnetic properties (Ms, Br and iHc) were measured by PPMS, indicates the existence of remanence magnetization reinforcing effect. By the demagnetization curves of the sintered magnets(δM-T), demonstrates the existence of intergrain exchange coupling among the nanograins.We found that SmCo₅ magnet was iHc of 2.8T, Sm₂Co₁₇ magnet was iHc of 0.86T, SmCo₁₃ magnet was iHc of 0.39T and Br of 0.9T. The SmCo₅ magnet exhibits a better thermal stability with the coercivity temperature coefficientβofï¹£0.146%/K. which show that SmCo₅ nanocrystalline magnets have good high temperature magnetic properties.