Effect of Zr Addition on Magnetic Properties of TbCu7-Type Sm–Fe–N Powder Synthesized by Low-Temperature Ca Reduction Diffusion Process

The effect of the addition of Zr on the magnetic properties of anisotropic TbCu7-type Sm–Fe–N powders prepared by the low-temperature reduction-diffusion (LTRD) process was investigated. At the reduction diffusion temperature of 873 K, the TbCu7-type Sm–Fe phase ratio decreased with an increase in the Zr content. At a higher reduction diffusion temperature of 973 K, a TbCu7-type Sm–Fe phase was obtained regardless of the amount of Zr added. Furthermore, the Th2Zn17-type Sm–Fe phase was obtained without the addition of Zr. Therefore, it was indicated that the addition of Zr can stabilize the TbCu7-type Sm–Fe phase at high temperatures. By nitriding the obtained powder, a TbCu7-type Sm–Fe–N powder was obtained; however, its magnetic properties deteriorated as the amount of Zr increased. Microstructural analysis revealed that the element ratio Zr/Sm in the TbCu7-type Sm–Fe–N particles saturated at approximately 0.05, and the excess Zr was consumed to form the ZrFe2 phase on the outside of the particles. It was concluded that the ZrFe2 phase results in the deterioration of the magnetic properties of the powder.