MICROSCOPIC PARAMETERS OF R-T HARD MAGNETS

R-T compounds with R=rare earth and T=transition metal have become the most important materials in modern hard magnet technology. The unusua l magnetic properties of these materials originate from the interplay between the strong crystal field anisotropy of the R atoms and the lar ge magnetization and exchange interaction of the T atoms. Inelastic ma gnetic neutron scattering can be employed to determine some relevant m icroscopic parameters of magnetic compounds. We discuss a case where t he crystal field interaction dominates the exchange interaction (NdCu2 , an intermetallic compound with low magnetic ordering temperature) an d compare it to the situation in R-T hard magnets where the exchange i nteraction J(RT) is much stronger than the crystal field interaction. We discuss the experimental results for RFe2 and R2Fe14B compounds and compare the microscopic parameters as deduced from different experime ntal methods and from ab initio calculations.