Microstructure, magnetic properties and magnetic hardening in 2 : 17 Sm–Co magnets

Abstract

Abstract A comprehensive and systematic study has been made on Sm(Co, Fe, M, L)z magnets (M = Cu or Ni, and L = Zr or Ti) to completely understand the effects of composition and processing on the microstructure and magnetic properties of magnets. Ti-containing magnets do not have a lamellar phase but exhibit only a cellular microstructure, resulting in a much lower coercivity (below 10 kOe). Ni-containing magnets exhibit a perfect cellular/lamellar microstructure, but without a large domain wall energy gradient at the interface of the 2 : 17 and 1 : 5 phases, leading to a low coercivity. Only in the magnets containing both Cu and Zr, a uniform and stable cellular/lamellar microstructure with a high domain wall energy gradient across the 1 : 5 phase is formed, resulting in high coercivity. These results indicate that the conditions for effective magnetic hardening are: (1) Formation of a cellular/lamellar microstructure, and (2) establishment of a domain wall energy gradient at the cell boundaries. Based on all of these experimental results, the magnetization reversal mechanism of 2 : 17 Sm–Co magnets can be explained by both the domain wall pinning and nucleation models. The nucleation mechanism holds at any temperature in the Cu-rich magnets, and only above the Curie temperature of the 1 : 5 phase in the alloys with the lower Cu content. In these cases, the 2 : 17 cells become magnetically decoupled.