(feco) <sub>, Nanocrystalline Two-phase Permanent Magnet Materials Of Pr <sub> 2 </ Sub> 14 </ Sub> B/¦Á- (feco) Magnetic And Micro-structure

Research in magnetism has long included, as a vital component, the discovery and development of ever more powerful and stable permanent-magnet materials. Nano-composite permanent magnets (NPMs), consisting of exchanged-coupled magnetically hard and soft phases in nano-scale, have drawn considerable attention in the last two decades, because of an enhanced remanence, a relatively high coercivity, and a high maximum energy product (BH)_max. In this thesis, we mainly describe our systematical investigation on the influence of low melting point metal additive on the hard magnetic properties of Pr₂(FeCo)₁₄B/α-(FeCo) NPMs, in addition with the influence on magnetization behavior and magnetic viscosity of the material. .The isotropic ribbons of nano-composite Pr₉Fe₇₄Co₁₂B₅ with additive of low melting point metals, such as Al, Zn, Sn, In or Ga, were prepared by melt spinning. It was found that, besides the expensive additive Ga can improve the magnetic properties of the sample, the remanence of the ribbons could be obviously improved at the expense of coercivity by the addition of economical Sn additive. The remanence J_r about 1.30T and maximum energy product (BH)_max about 20.5 MGOe were obtained in Pr₉Fe₇₄Co₁₂B₅Sn_0.5, while J_r and (BH)_max in Pr₉Fe₇₄Co₁₂B₅ ribbons were about 1.17 T and 17.9 MGOe, respectively. By increasing the content of magnetically hard phase, the intrinsic coercivity _iH_c can be elevated. Thus, the optimum magnetic properties, such as J_r=1.27 T, _iH_c=5.7kOe and (BH)_max =22.5 MGOe were obtained in Pr_9.5Fe_73.57Co_11.93B₅Sn_0.5 ribbons. Transmission electron microscopy results reveal that the additive Sn is located at the grain boundaries rather than in grain interior in Pr₉Fe₇₄Co₁₂B₅Sn_0.5 ribbons. The obvious improvement of the remanence originates from the refinement of the microstructure and the increase of soft phase content by Sn addition.The annealing method of YAG laser heat treatment of the Pr₂(FeCo)₁₄B/α-(FeCo) as-spun ribbons was also studied. We obtained a good magnetic properties of J_r =1.25T, ,H_c =5.7 kOe, (BH)_max=22.5MGOe in Pr₉Fe₇₄Co₁₂B₅Ga ribbons. Meanwhile, the ribbons were found to be little oxidized even in a higher oxide atmosphere than that of the conventional annealing method.In order to research the magnetization behavior and magnetic viscosity in nanocomposite Pr₉Fe₇₄Co₁₂B₅Sn_x(x=0, 0.5) ribbons, measurements of reversible and irreversible...