Enhanced Thermal Stability of Nd–Fe–B Sintered Magnets by Intergranular Doping Y72Co28 Alloys

The intergranular addition process using Y₇₂Co₂₈ eutectic alloy powders has been applied to (Pr, Nd)₂₇Dy₄Fe_67.65Cu_0.15Al_0.2B₁(wt.%) sintered magnets, resulting in an enhanced thermal stability. It was found that the coercivity of magnets at 100 °C increased while the addition of Y₇₂Co₂₈ is 1 wt.%, whereas the magnetic properties decreased slightly at room temperature due to lower magnetocrystalline anisotropy field (H_A ) of Y₂Fe₁₄B. The temperature coefficient of remanence (α ) and coercivity (β) for the magnets improved significantly. Microstructure observation indicated that Y atoms prefer to enter into the 2-14-1 phase and form a core-shell structure with an outer layer of (Nd, Dy, Y)₂(Fe, Co)₁₄B. Magnetic domain and intrinsic properties analysis suggested that the improved thermal stability resulted from the modified grain boundaries and the introduction of Y in matrix phases.