Studies of microstructure and magnetic properties in sintered mixed rare earth (MRE) -Fe-B magnets (MRE NdLaDy)

Sintered Nd_0.45(La_rDy₁) _{1/(r1)0.552.6}Fe₁₄B magnets (r 1 to 3) were studied. Magnetic properties and microstructures of the magnets were investigated by magnetic measurements and electron microprobe analysis. The microstructure of magnets consists of a mixed rare-earth (MRE) ₂Fe₁₄B (2: 14: 1) phase matrix having a grain size of ∼8 m and a rare earth (RE)-rich grain boundary phase. The grain boundaries are rich in La and Nd but depleted in Dy, while the La, Nd, and Dy contents are constant across the 2: 14: 1 grains. The coercivity and temperature stability of magnets are improved with increasing Dy content. A (BH)_max of 21.1 MGOe at room temperature is obtained in the magnet with r 1. Temperature coefficients of α= -0.06 and β= -0.48 C were also obtained, which is comparable to those of Nd-based magnets with the best temperature stability. Unfortunately, the improvement of coercivity and its temperature coefficient is mainly achieved by adding greater amounts of Dy and DyF₃, which leads to low (BH)_max values and high magnet costs.