Fundamentals of Magnetic Anisotropy in Rare Earth-Iron Intermetallic Compounds

Abstract

The magnetic anisotropy of rare earth — transition metal intermetallic compounds can be largely understood on the basis of crystal field theory, which provides a good phenomenological basis for understanding and interpreting the magnetic anisotropy of the rare earth elements. In this chapter we give an introduction to the analysis of magnetic anisotropy in the rare earth-iron Laves phase (RFe2) intermetallic compounds, which are useful as magnetostrictive device materials and for which a relatively large body of data exists. From a crystal field point of view these compounds are relatively simple, with cubic symmetry and only a single type of rare earth site. Although the magnetic anisotropy behavior and spin reorientations with temperature and composition are rather complex, they can be understood quite well using molecular field theory with only the two cubic crystal field parameters and a single exchange parameter, and by taking into account the magnetostrictive contribution to the anisotropy. Neutron inelastic scattering measurements of the excitation spectrum show clearly that one of the reasons mean field theory works so well for these materials is that the low lying magnetic excitations are exactly mean-field-like over almost all the Brillouin zone, in contrast to a typical elemental ferromagnet such as nickel or iron where the magnetic excitations are quite dispersive over the entire zone.