Materials with specific and future hard magnetic properties

The property levels achieved by alnico magnets (first appearing in the late 1930s), hard ferrites (1950s) and above all those of samarium-based compounds (SmCo ₅ then Sm ₂ (CoFeCuZr) ₁₇ ; early and late 1970s) and neodymium-based (Nd-Fe-B; 1983) materials have enabled and continue to enable a wide diversification of increasingly high-performance systems, often with a significant reduction in size, weight and even price. These four families of materials are at the heart of today's modern magnets.

If we look at the development of magnets since the beginning of the 20th century, these four families are the only ones to have really been able to open up industrial opportunities; others, less efficient, have either disappeared or been confined to restricted fields of application. But if we consider the research carried out in the last decade of the twentieth century and look ahead to the years to come, it appears that the two families of rare-earth-based materials are likely to be enriched by promising new grades.

We feel it's important to keep a record of the permanent magnet materials that, in their time, contributed to the development of the technology. That's why, in the first part of this article, we briefly describe some of these alloys, now obsolete or little used. The second part of the article describes some of the new grades being studied in the laboratories, some of which are about to enter industrial development.