Berlin 2005 – wissenschaftliches Programm

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MA: Magnetismus

MA 19: Mikro- und nanostrukturierte magn. Materialien I

MA 19.5: Vortrag

Montag, 7. März 2005, 11:30–11:45, TU EMH225

Structure and Magnetic Properties of Nanocrystalline Fe_100−xPt_x Powders — •Julia Lyubina, Oliver Gutfleisch, Karl-Hartmut Müller, and Ludwig Schultz — IFW Dresden, Institute for Metallic Materials, P.O. Box 270016, D-01171 Dresden, Germany

The ordered tetragonal L1₀ FePt phase has excellent intrinsic magnetic properties (K₁ = 6.6 MJm⁻³, J_s = 1.43 T, T_c = 750 K), good mechanical properties and corrosion resistance. The combination of these unique properties makes it interesting both from the scientific and application points of view. Here we report on the preparation of nanocrystalline hard magnetic Fe_100−xPt_x (x = 39.5; 45; 50; 55; 60) powders by mechanical ball milling at 77 K followed by annealing (450 ⁰C). According to Rietveld refinement of x-ray data, annealed powders contain a mixture of the highly ordered L1₀ FePt and disordered cubic A1 FePt, as well as Fe₃Pt and FePt₃. The amount of the A1 FePt phase remains almost unchanged (6-10 vol. %), whereas the fraction of the L1₀ FePt, Fe₃Pt and FePt₃ phases varies with Pt concentration x. Coercivity µ₀H_c was found to increase with Pt concentration from 0.33 T (x = 39.5) to 0.95 T (x = 60), whereas remanence J_r reduce: from 0.8 T (x = 39.5) to 0.4 T (x = 60). In Fe-rich powders exchange-spring behaviour was observed. The evolution of magnetic properties is discussed in terms of phase composition, distribution of the phases and degree of chemical order.