Effects of terbium sulfide addition on magnetic properties, microstructure and thermal stability of sintered Nd—Fe—B magnets

To increase coercivity and thermal stability of sintered Nd-Fe-B magnets for high-temperature applications, a novel terbium sulfide powder is added into (Pr_0.25Nd_0.75)_30.6Cu_0.15Fe_balB₁ (wt.%) basic magnets. The effects of the addition of terbium sulfide on magnetic properties, microstructure, and thermal stability of sintered Nd-Fe-B magnets are investigated. The experimental results show that by adding 3 wt.% Tb₂S₃, the coercivity of the magnet is remarkably increased by about 54% without a considerable reduction in remanence and maximum energy product. By means of the electron probe microanalyzer (EPMA) technology, it is observed that Tb is mainly present in the outer region of 2:14:1 matrix grains and forms a well-developed Tb-shell phase, resulting in enhancement of H_A, which accounts for the coercivity enhancement. Moreover, compared with Tb₂S₃-free magnets, the reversible temperature coefficients of remanence (α) and coercivity (β) and the irreversible flux loss of magnetic flow (h_irr) values of Tb₂S₃-added magnets are improved, indicating that the thermal stability of the magnets is also effectively improved.