Regensburg 2004 – scientific programme

Parts | Days | Selection | Search | Downloads | Help

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 Schultz¹ — ¹IFW 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 (J_s = 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 Fe_50+xPt_50−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 µ_0JH_c = 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.