Magnetic Properties of $Nd_{12}Fe_{82}B_6$ and $Nd_{14}Fe_{80}B_6$ Powders Obtained by High Temperature Milling

The present paper describes a comparison of magnetic properties of $Nd_{12}Fe_{82}B_6$ and $Nd_{14}Fe_{80}B_6$ powders obtained by a new method of processing of Nd-Fe-B powders - high temperature milling. In this method the milling operation is carried out, entirely or only in the final stage, at high temperatures, so that the destruction of the $Nd_2Fe_{14}B$ phase and its recombination occur simultaneously. In this way a powder with good magnetic properties immediately after milling was obtained. In the present experiments, the powder was subjected to high-energy milling for 17 h (until the material becomes amorphous) and then, the milling was continued for 0.5 h with the powder container being heated to an appropriate temperature or milled at high temperature during whole time of the process. Diffraction examinations have shown that the powder processed in this way contains the $Nd_2Fe_{14}B$ phase. Its magnetic properties appear to depend on the applied temperature or milling time (at optimum temperature). The used method of processing leads to obtaining high-coercivity Nd-Fe-B powders. The magnetic properties of the material thus produced, in particular its coercivity, strongly depend on the milling temperature and milling time.