Recent advances in pseudobinary iron based permanent magnets

Abstract

Only recently has it been possible to make iron based analogues to Sm-Co based compounds that exhibit energy products of greater than 20 MG De. These compounds have generally been in the form of pseudobinaries since some other element is required either to help stabilise the crystal structure or to modify the anisotropy of the base compound. The discovery of the ternary phase Nd₂Fe₁₄B was a tremendous step forward since it was the first Fe-based compound that utilised the high intrinsic magnetisation of Fe and large anisotropy of a rare earth element to allow very high energy density magnets to be made. But the relatively low Curie point prompted the continuing search for higher Curie point, high anisotropy, Fe-based compounds. Recently five Fe-based compounds have been modified through the incorporation of a third element into the structure to allow the synthesis of new high energy product, greater than 20 MG De, Fe-based magnetic materials. These systems include the compounds Sm₂Fe₁₇N_3-8, Sm(Fe,Ti)₁₂ Nd(Fe,Co,Ti)₁₂N, Nd(Fe,Co,Mo)₁₂N, and Pr(Fe,Co,Mo)₁₂N. Four of these systems use the incorporation of a small atom such as N into the structure to change the anisotropy dramatically. Some of the progress and difficulties in synthesising these new Fe-based supermagnets are described.