Al,Ga substitution in RE2Fe17 (RE=Ce,Pr,Nd): Magnetic behavior of RE2Fe15(Al,Ga)2 alloys

Alloys with the composition RE2Fe17 and RE2Fe15X2 (X=Al,Ga) have been synthesized by the arc-melting technique followed by an 125-h anneal at 900–1000 °C in evacuated silica capsules. The new compound Nd2Fe15Ga2 is unstable below 800 °C, and is only obtained by quenching from above 900 °C. From x-ray powder diffraction analysis all alloys except Pr2 Fe15 Ga2 were found to crystallize with the hexagonal Th2 Zn17 type; indications for a preferential occupation of the (6c) sites by the X atoms are small. Substitution of Al, Ga atoms generally leads to a large increase of the Curie temperature and of the magnetocrystalline anisotropy, thereby enhancing the remanence as well as the coercivity. These effects are a consequence of the strongly distance-dependent exchange interactions of the Fe-Fe and Fe-RE coupling mechanisms. As for binary Pr2 Fe17 , the easy axis of magnetization for Pr2 Fe15 Al2 was found to be in the basal plane.