Magnetic Properties of Interstitially Modified Ce–Nd–Fe–Mo–N Magnets Prepared by Spark-Plasma Sintering

Abstract

Ce–Nd–Fe–Mo nitrides with tetragonal ThMn12-type structures are promising compounds for hard magnetic applications. The key to enhance magnetic performance is the insertion of a light element, such as N into the 2b site of the crystal lattice. However, the nitrogenation also changes the thermodynamic stability of Ce–Nd–Fe–Mo whose nitride will disproportionate at elevated temperature. This drawback poses a serious challenge to the sintering of bulk magnets. In this paper, we applied spark-plasma sintering (SPS), a rapid powder consolidation technique, to preparing bulk Ce–Nd–Fe–Mo–N magnets, and developed suitable sintering parameters through thermal analysis, X-ray diffraction, and magnetic property measurement. Without using any binder or additive, we demonstrated a dense magnet that features $H_{\mathrm {ci}} =3.34$ kOe, remanence $B_{r} =6.55$ kG, magnetization $4\mathrm {\pi }M_{19} = 9.12$ kG, and energy product $(BH)_{\mathrm {max}} = 4.98$ MGOe at room temperature, a performance that shows no degradation compared with the as-nitrided powder. Hence, it is anticipated that an SPS technique is applicable to sintering like metastable or reactive materials, such as (Ce, Nd)–(Fe, Co)–B for their sought-after functional properties.