Effect of C addition on the magnetic properties, phase evolution, and microstructure of melt spun ribbons

The effect of C addition on the magnetic properties, phase evolution, and microstructure of Hf-containing SmCo7−xHfx ( x = 0.1 – 0.3 ) ribbons via a melt spinning technique under sufficient supercooling conditions has been investigated. A small amount of C addition not only effectively refines the grain size from 100–400 nm for C-free to 20–60 nm for C addition, but also brings extremely fine high-magnetization fcc-Co grains (5–10 nm), and it eventually enhances the exchange coupling effect between grains. As a result, magnetic properties are enhanced markedly. When the C content exceeds 0.12, the larger amount of 2:17 phase and nonmagnetic Sm2C3 phase appear and, consequently, the permanent magnetic property of the ribbons is degraded.