Novel Permanent Magnetic Materials

Materials for high-performance permanent magnets must have a high Curie temperature, a large spontaneous magnetization and strong uniaxial magnetocrystalline anisotropy. Binary rare earth iron intermetallics are deficient in one or more of these respects. New series of rare-earth intermetallic compounds may be generated from existing series by a process known as gas-phase interstitial modification, whereby interstitial atoms such as nitrogen or carbon are introduced into the structure by reaction of a powder of the intermetallic with an appropriate gas. The interstitials occupy sites adjacent to the rare earth, thereby creating a crystal field that reflects the new local symmetry. They also expand the lattice, which greatly enhances the Fe-Fe exchange interactions, and may increase slightly the iron moment. These effects are discussed in detail for four systems, R₂Fe₁₇N_3-δ, R₂Fe₁₇C_3-δ R(Fe₁₁ Ti)N_1-δ and R(Fe₁₁ Ti)C_1-δ (R = rare earth), all of which include compounds with potential for making new parmanent magnets.