The effect of F substitution on the magnetic properties of Nd−Fe−B based compounds

Various efforts are currently undertaken to raise the relatively low Curie temperature of the otherwise promising Nd?Fe?B type permanent magnet material. The substitution of Fe by several elements was found to increaseT _c, which, on the other hand, can be accompanied by a reduction of the magnetocrystalline anistropy. In the present paper a systematic Mössbauer study was carried out, using Co, Ni, Al, Si and Ga as substituents. The specific influence of each element upon the magnetic properties is attributed to its preference for entering a certain Fe lattice site. Simple atomic size considerations are proved to be insufficient for explaining the preferred occupation observed experimentally. Obviously the local electronic structure has to be studied more carefully. Finally, the interplay between magnetism and metallurgy (particularly the formation of precipitations), is found to be of some importance.