Hard magnetic properties of melt-spun R(Fe,M)(12) nitrides (R=Nd or Pr; M=Mo or V)

The hard magnetic properties of nitrided melt-spun R(Fe,M)(12) (R = Pr and Nd, M = V and Mo) ribbons have been investigated. Hard magnetic powders wer e prepared by vacuum annealing of ground ribbons in the temperature range f rom 700 to 950 degrees C and subsequent nitrogenation. For NdFe10.5Mo1.5Nx and PrFe10.5Mo1.5Nx powders, coercivities as high as 10.4 and 4.5 kOe at ro om temperature, respectively, were achieved by carefully controlling the ni trogenation process. The coercivity strongly depends on the preparation rou te, i.e., annealing temperature as well as nitrogenation temperature and ti me. By the detailed investigation of the influence of these conditions, the optimum process parameters were determined. The coercivity mechanism of me lt-spun NdFe10.5Mo1.5Nx powders shows characteristics of a randomly oriente d single domain particle system. Poor coercivities have been obtained for N d(Fe,V)(12) and Pr(Fe,V)(12). In these cases as well as for not optimally n itrogenated Nd(Fe,Mo)(12), the low coercivity of the nitrided powders is re lated to (i) too large grain sizes, (ii) the presence of alpha-Fe additiona l to the ThMn12-type phase, or (iii) a nonhomogeneous nitrogenation of the powder. (C) 2000 American Institute of Physics. [S0021-8979(00)05614-0].