Study On The Microstructure And Magnetic Properties Of M-Nd-Fe-B?M=Pr,Co,Dy,Tb?/Fe₇Co₃ Nanocomposite Materials

Nanocomposite magnetic materials consist of soft magnetic phase which has higher saturation magnetization and hard magnetic phase which has higher magnetocrystalline anisotropy have become new types of high-performance permanent magnet materials.Due to magnetic coupling in nanoscale between soft magnetic phase and hard magnetic phase,nanocomposite can achieve very high coercivity,and it also has been used widely in modern industry,science and technology fields for their favourate magnetic properties.The quantity of product demanded increase year by year,but it has some disadvantages like the low Curie temperature and the weak thermal stability.In this paper,Fe₇Co₃ powders were prepared by gas atomization under liquid nitrogen atmosphere,then Nd-Fe-B/Fe₇Co₃ nanocomposite had been prepared by melt-spinning method.In order to improve the magnetic properties of ribbons,adding a single or multiple elements and adjusting the correlative technical parameters were applied.The conclusion is that the phase composition of the ribbons for Pr addition were composed of Pr₂Fe₁₄B hard magnetic phase and Fe₇Co₃ soft magnetic phase.After hot annealing at 720?,the exchange coupling interaction between neighbouring grains became largest and the magnetic properties of the ribbons became best,which was Hci of 4994.3 Oe,?_r of 47.9 emu/g,the remanence ratio?_r/?_s of 0.41.For Pr-Nd-Fe-B/Fe₇Co₃ nanocomposite,Co addition changed the interaction of 3d-4f electrons between Fe and rare earth,turned the negative exchange integral between Fe-Fe into the positive exchange integral between Fe-Co,raised the exchange coupling,improved the Courier temperature and enlarged the applied range in high temperature for Nd-Fe-B nanocomposite.Co instead of Fe made the hole numbers of the 3d⁺accessory energy band reduced and the hole numbers of the 3d^-accessory energy band increased,so the saturation magnetization increased.With the added element of 4 at.%Co,the magnetic properties were best,which was H_ci of 5986.1 Oe,?_r of 51.7 emu/g,the remanence ratio?_r/?_s of 0.48.After adding the heavy rare earth element Dy and Tb,?Dy,Pr,Nd?₂?Fe,Co?₁₄B and?Tb,Nd?₂?Fe,Co?₁₄B compound with the higher magnetocrystalline anisotropy field were formed,Hci can improve enormously.Due to the element of Co,the remanence and the saturation magnetization reduced little relatively.When the element of Dy was 0.2%,the element of Tb was 0.3%,the magnetic properties were best,which was H_cii of 7237.9 Oe,?_r of 60.5 emu/g,the remanence ratio?_r/?_s of 0.54 and H_ci of 7512.9 Oe,?_r of 59.3 emu/g,the remanence ratio?_r/?_s of 0.55,respectively.Futhermore,the influence on the magnetic properties of different quick quenching speeds were studied.The phase composition of ribbons for the fast wheel speed were composed of soft magnetic phase and amorphous phase.After crystallization,the microstructure with the thin and uniform grains was achieved,the exchange coupling interaction strengthened,which gained the favourable magnetic properties.