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Regensburg 2004 – scientific programme

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MA: Magnetismus

MA 26: Mikro- und nanostrukturierte Materialien

MA 26.3: Talk

Thursday, March 11, 2004, 15:45–16:00, H10

Nanocrystalline hard magnetic FePt powders — •Julia Lyubina1, Oliver Gutfleisch1, Nora M. Dempsey2, Axel Handstein1, Karl-Hartmut Müller1, and Ludwig Schultz11IFW Dresden, P.O. Box 270016, D-01171 Dresden, Germany — 2Laboratoire Louis Neel, 25 Avenue des Martyrs, BP 166, 38042, Grenoble, France

The ordered FePt (L10) compound possesses high magnetocrystalline anisotropy (K1 = 6.6 MJm−3) and saturation polarisation (Js = 1.43 T), as well as excellent mechanical properties and corrosion resistance. Thus, it is a promising candidate for permanent magnet applications, for instance in micro-electromechanical systems (MEMS). In the present work we report on the preparation of nanocrystalline hard magnetic Fe50+xPt50−x (x = 0; 5; 10.5) powders by mechanical milling at liquid nitrogen temperature followed by annealing. The evolution of phase composition, chemical order, and magnetic properties is studied as a function of composition and annealing conditions. All the powders contain a mixture of highly ordered L10 FePt (up to 90 vol. %), disordered FePt, as well as Fe3Pt and FePt3 phases. The highest coercivity of µ0JHc = 0.7 T was achieved in the Fe50Pt50 powder annealed at 450 0C for 48 h, which is substantially higher compared to that of conventional bulk FePt. The microstructure of the annealed FePt powders has a lamellar character with a typical grain size of about 40 nm. The coercivity increases with increasing volume fraction of the L10 phase and degree of chemical order. The authors are grateful to the DFG SFB 463 for financial support.

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