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MA: Magnetismus

MA 8: Hart- und Weichmagn. Materialien / Legierungen

MA 8.2: Vortrag

Dienstag, 12. März 2002, 14:00–14:15, H10

High performance nanocrystalline (Pr,Nd)FeB-based magnets produced by intensive milling — •A. Bollero¹, O. Gutfleisch¹, K.-H. Müller¹, L. Schultz¹, G. Drazic², and S. Kobe² — ¹IFW Dresden, Institut für Metallische Werkstoffe, Postfach 270116, D-01171 Dresden, Germany — ²Jozef Stefan Institute, Jamova 39, 1001 Ljubljana, Slovenia

Intensive milling has been used to produce nanocrystalline isotropic (Pr,Nd)FeB-based powders. The influence of Dy and Zr, and the substitution of Pr by Nd, on the structural and magnetic properties have been studied. Reduction of R-content, increase of T-content and presence of Co in the starting composition led to an improved performance: J_r = 0.92 T, µ₀H_c = 1.25 T and (BH)_max = 140 kJ/m³ for Pr₉Nd₃Dy₁Fe₇₂Co₈B_6.9Zr_0.1 due to a fine microstructure with a mean grain size of 20 nm. Intensive milling has shown to be a versatile technique to produce high performance nanocomposite magnets by blending this alloy with different fractions of α-Fe. 25wt.%Fe addition resulted in an optimum combination of magnetic properties with (BH)_max = 178 kJ/m³ due to an effective exchange coupling between the hard and soft magnetic phases. A T_C of about 365^∘C was found. Demagnetization recoil loops of both, single-phase and nanocomposite magnets, showed clear differences due to the exchange-spring mechanism present in the latter. δJ plots for the nanocomposite magnets showed a negative deviation of the demagnetizing remanence from the Wohlfarth model indicative of exchange coupling interactions being dominant.