High-Temperature Samarium Cobalt Permanent Magnets

This chapter reviews the development of SmCo-type magnets over the last 40 years. First, the physical metallurgy and crystal structures are considered; then the focus is on the recent developments in high-temperature Sm(CobalFewCuxZry)(z) magnets suitable for operation temperatures up to 500 degrees C. It is elucidated that the evolution of coercivity and microchemistry in the respective phases of the heterogeneous nanostructure as well as magnetic domain structure is very sensitive to details of the processing procedure, especially to the slow cooling ramp as the last step where the hard magnetic properties evolve. These changes give rise to rather complex pinning mechanisms in a three-phase precipitation structure, which again depend in a subtle manner on the microchemistry of the 1:5-type cell boundary phase in the 2:17-type magnets. It is the amount and distribution of Cu in and at the cell boundary phase which is the prevalent factor determining the pinning strength and which can yield a non-monotonic temperature dependence of., coercivity. The chapter concludes with an overview of novel non-equilibrium processing routes used to obtain SmCo-type nanocomposites.