Preparation,structure And Magnetic Properties Of Anisotropic Bulk Smco₇-Type Nanocomposite Permanent Magnets

SmCo₇-type permanent magnet materials have attracted much scientific and technological interest due to their excellent high temperature characteristics and great potential in high temperature field.However,the bulk magnet of SmCo₇ is isotropic,while the theoretical energy product of isotropic permanent magnet is only 1/4 of anisotropic permanent magnet.It has always been a huge scientific problem to generate?00l?texture in the bulk SmCo₇ nanocrystalline permanent magnets.We have prepared the anisotropic nanocrystalline permanent magnetic materials of SmCo₇ and SmCo₇/?-?Fe,Co?with?00l?texture by the strong deformation coupled with multifield,such as the temperature gradient field,the stress field and strain field.A great breakthrough has been achieved in both the performance and structure.In this paper,the microstructure and magnetic properties of the anisotropic nanocrystalline permanent magnets are studied by X-ray diffraction,transmission electron microscopy,high-resolution transmission electron microscopy and vibrating sample magnetometer.The nucleation of the hard phase is optimized during the strong deformation technology coupled with multi-field.The anisotropic bulk nanocrystalline permanent magnet of SmCo₇ with?00l?texture is successfully prepared.The grain size is successfully controlled below 20 nm.The coercivity of the anisotropy nanocrystalline magnetic materials of SmCo₇ is 10.3 kOe and the remanence ratio is 0.81,M_r^///M_r^?=1.4.The maximum energy product is 18.4 MGOe,which is 40%higher than of the reported highest energy product(?BH?_max=13 MGOe).Through the strong deformation technology coupled with multifield,the nucleation of SmCo₇ is optimized in the deformation process.For the first time,the anisotropic bulk nanocomposite magnet of SmCo₇/?-?Fe,Co?with a?00l?texture is successfully prepared and the grain size is successfully controlled to below¹0 nm.When the soft magnetic phase content is 28 wt%and the deformation is 80%,the coercivity of the anisotropic nanocomposite magnet is 4.6 kOe and the remanence ratio is 0.91,M_r^///M_r^?=1.4.The maximum energy product is 28 MGOe,which is 115%higher than the energy product of the reported highest energy product(?BH?_max=13 MGOe).The effect of stress and strain on the growth of?00l?texture is described theoretically by molecular dynamics simulation.The high temperature characteristics of the deformed bulk SmCo₇ and SmCo₇/?-?Fe,Co?nanocomposite magnets was studied.The temperature coefficient?_RT-300T-300 o_C of coercivity of anisotropic nanocrystalline SmCo₇ is-0.19%/^oC,which is 27%higher than the coercivity temperature coefficient of the commercial SmCo₅ magnet(?_RT-300T-300 o_C=-0.26%/^oC).The coercivity temperature coefficient of the anisotropic SmCo₇/?-?Fe,Co?bulk nanocomposite magnet with 28%content of the soft magnetic phase is-0.25%/^oC,which is equivalent to the coercivity temperature coefficient of the commercial SmCo₅(?_RT-300T-300 o_C=-0.26%/^o C).Meanwhile,the experimental results showed that the anisotropic nanocomposite magnet of SmCo₇/?-?Fe,Co?with 28%soft magnetic phase exhibits excellent structural stability at 350 ^oC and 400 ^oC.Finally,the magnetic property of the anisotropic bulk nanocomposite magnets of SmCo₇/?-?Fe,Co?with different content of the?-?Fe,Co?phase is studied.