New developments in hard magnetic materials

TLDR

The review surveys the formation, crystal structures, and magnetic properties of rare‑earth intermetallics such as R₂Fe₁₄B, R₂Fe₁₄C, R₂Co₁₄B, and ThMn₁₂‑type ternaries that serve as starting materials for permanent magnets. It explains the magnetic behavior through inter‑ and intra‑sublattice exchange and the competition between rare‑earth and 3D sublattice anisotropies, and reviews manufacturing routes, coercivity mechanisms, and cost‑performance trade‑offs for various magnet types. The review highlights that interstitial incorporation of C or N into R₂Fe₁₇ compounds markedly alters their magnetic properties.

Abstract

A review is given of the formation, the crystal structure and the magnetic properties of several classes of rare earth based intermetallic compounds that lend themselves as starting materials of permanent magnets. These compounds include R2Fe14B, R2Fe14C and R2Co14B and the large class of ternary rare earth compounds having the tetragonal ThMn12 structure. Special emphasis is given to the changes in magnetic properties of R2Fe17 compounds observed after interstitial solution of C or N atoms. The magnetic properties of all these compounds are discussed in terms of current models based on intersublattice and intrasublattice exchange and the interplay between the rare earth sublattice anisotropy and 3D sublattice anisotropy. A substantial portion of the review is devoted to manufacturing routes of permanent magnets and a description of the coercivity mechanisms operative in the magnets. A comparison is made of the performance and economic costs of various types of magnets and novel applications are briefly discussed.