Microstructure of Zinc-Bonded Sm₂Fe₁₇N₃ Permanent Magnet Studied by Transmission and Analytical Electron Microscopy

Abstract

Microstructure of the Zn-bonded Sm₂Fe₁₇N₃ permanent magnet having high magnetic coercivity of 11.8 kOe was studied by transmission and analytical electron microscopy. Three phases, α-Fe including 20 to 30 at%Zn, Fe₃Zn₇, and Sm₂(Fe, Zn)₁₇N_x, were found in addition to the matrix Sm₂Fe₁₇N₃ phase. The Sm₂(Fe, Zn)₁₇N_x phase, in which a fraction 0.2 of Fe in Sm₂Fe₁₇N₃ is replaced by Zn, surrounds the matrix grains and protects them from coming into contact with the α-Fe grains, which are considered to act as nucleation sites of reverse magnetic domains. It was concluded that the existence of the Sm₂(Fe, Zn)₁₇N_x phase causes the high coercivity.