magnetic anisotropy; spin-orbit coupling

作者:R.Skomski;D.J.Sellmyer;
关键词:magnetic anisotropy; spin-orbit coupling; crystal-field

interaction; interstitial modification; permanent magnets; rare

earths
单位:Department of Physics and Astronomy, NCMN, University of

Nebraska;
摘要:Rare-earth intermetallics Neodymium Magnets
http://www.999magnet.com/products/110-sintered-neodymium-magnets such as Nd2Fe14B and Sm-Co are

widely used as high-performance permanent magnets, because they

combine high magnetocrystalline anisotropy with reasonable

magnetization and Curie temperature. The anisotropy is a combined

effect of spin-orbit coupling and electrostatic crystal-field

interactions. The main contribution comes from the rare-earth 4f

electrons, which are well-screened from the crystalline

environment but exhibit a strong spin-orbit coupling. In this

limit, the magnetocrystalline anisotropy has a very transparent

physical interpretation, the anisotropy energy essentially being

equal to the energy of Hund's-rules 4f ion in the crystal field.

The corresponding expression for the lowest-order uniaxial

anisotropy constant K1 is used to discuss rare-earth

substitutions, which have recently attracted renewed interest due

to shifts in the rare-earth production and demand. Specific

phenomena reviewed in this article are the enhancement of the

anisotropy of Sm2Fe17 due to interstitial nitrogen, the use of

Sm-Co magnets for high-temperature applications, and the

comparison of rare-earth single-ion anisotropy with other single

-ion and two-ion mechanisms.