New NdFeB-based bulk "exchange spring"-type permanent magnets. Experimental and micromagnetic FORC analysis

Summary form only given. This paper focuses on the possibility of direct casting miniature NdFeB-based bulk permanent magnets in different three-dimensional shapes for various applications, with amorphous structure followed by subsequent optimal annealing. Nd₃Dy₁Fe₆₆Co₁₀B₂₀ bulk nanocomposite permanent magnets in form of rods with diameters ranging from 0.5 to 0.8 mm have been prepared by devitrification annealing of amorphous and partly-amorphous precursors produced by injection die-casting. A fully amorphous structure was obtained for rods with the diameter as large as 0.6 mm. The best-achieved magnetic properties have been obtained for the optimum devitrification (15 min at 630degC) samples with 0.6 mm diameter, and are: H_C,5T = 316 kA/m, mu₀M_r,6T= 1.04 T, M_r/M_max,6T=0.68 and (BH)_max,6T=98 kJ/m³. The samples were characterized using the first-order reversal curve diagram (FORC). The micromagnetic simulation reproduced the experimental results.