Study On The Structure And Magnetic Properties Of Nd-Fe-M-B (M=co, Cr, Al, Zr) Ribbon Magnets

The nanocomposite permanent magnetic materials are multi-phase magnets which are composed of soft magnetic phases with high saturated magnetization and hard magnetic phases with high anisotropy field. Due to the outstanding magnetic properties obtained by means of exchange-coupling interaction between soft magnetic phases and hard magnetic phases, these magnetic materials can be potentially used in broad areas. In this paper, the ribbon magnets were prepared by melt-spinning method, the X-ray diffractometer, electron microscope, thermal analyzer and vibrating specimen magnetometer etc were used to study the element substitution of Nd₂Fe₁₄B-type magnets. The effects of M=Co, Cr, Al, Zr and melt-spinning speeds on the structure and magnetic properties of Nd-Fe-M-B ribbon magnets were mainly discussed.It was found that when a given amount of Co was added into the Nd-Fe-B alloy, the remanence of Nd₁₀Fe₈₁B₆Co₃ ribbons melt spun at 35 m/s and followed by annealing at 800 oC for 20 min was increased from 52.9 emu/g of the Nd10Fe84B6 ribbons to 84.3 emu/g, while the coercivity of annealed Nd₁₀Fe₈₁B₆Co₃ ribbons was decreased slightly.The Nd_11.3Fe_80-xB_5.2Co_3.5Mx alloys were prepared by substituting Cr, Al or Zr for Fe in the Nd_11.3Fe₈₀B_5.2Co_3.5 alloy. It was found that all alternative elements can facilitate the formation of amorphous phase differently. When the Nd_11.3Fe_80-xB_5.2Co_3.5Mx ribbons were melt spun at 35 m/s and followed by annealing at 800 oC for 20 min, the magnetic properties of the annealed ribbons with M=Cr and x=0.4 have the coercivity (Hc) of 5375.7 Oe, maximum magnetization (Ms) of 149.2 emu/g, remanence (Mr) of 96.5 emu/g and remanence ratio (Mr/Ms) of 0.65; While the magnetic properties of the annealed ribbons with M=Al and x=1.5 are Hc=7227.8 Oe, Ms=99.4 emu/g, Mr=96.5 emu/g and Mr/Ms=0.51; Furthermore, the magnetic properties of the annealed ribbons with M=Zr and x=2 amount to much better values: Hc= 9311.4 Oe, Ms=190.1emu/g, Mr=116.4 emu/g and Mr/Ms=0.61.When the Nd₁₀Fe₈₁Co₃B₆ alloy were melt-spun at the speeds of 15 m/s, 35 m/s and 50 m/s respectively, it was found that the content of amorphous phase was increased with increasing the melt-spinning speed. After the Nd₁₀Fe₈₁Co₃B₆ ribbons were annealed at 800oC for 10min, the annealed ribbons melt-spun at 35m/s were fully crystallized and the best exchange coupling action was built up, then the coercivity of annealed ribbons amounted to 3139.8 Oe, the remanence reached 84.3 emu/g. In addition, the Curie temperature of main phase Nd2(Fe,Co)14B was little affected by melt-spinning speed, it's about 630K in the ribbons melt-spun at three different speeds.