* Corresponding author. Tel.: #43-1-58801-13730; fax: #43-1-58801-13798. E-mail address: bernardi@email.tuwien.ac.at (J. Bernardi). Journal of Magnetism and Magnetic Materials 219 (2000) 186}198 Preparation, magnetic properties and microstructure of lean rare-earth permanent magnetic materials J. Bernardi*, T. Schre#, J. Fidler, Th. Rijks, K. de Kort, V. Archambault, D. Pe H re H , S. David, D. Givord, J.F. O'Sullivan, P.A.I. Smith, J.M.D. Coey, U. Czernik, M. Gro K nefeld Institut fu ( r Angewandte und Technische Physik, Vienna University of Technology, Wiedner Hauptstr. 8-10, A-1040 Wien, Austria Philips Research, Building WA12, Prof. Holstaan 4, NL 5656 AA Eindhoven, The Netherlands Rhodia Recherches, Centre de Recherches d+Aubervilliers 52, Rue de la Haie Coq, F-93308 Aubervilliers, France CNRS, Laboratoire Louis Ne & el, 25 Auvenue des Martyrs, B.P. 160, F-38000 Grenoble, France Department of Physics, Trinity College, Dublin 2, Ireland Magnetfabrik Bonn, Dortheenstra}e 215, P.B. 2005, D-52010 Bonn, Germany Received 22 November 1999; received in revised form 26 May 2000 In memory of Kees de Kort Abstract Nanocrystalline, lean rare-earth composite alloys around the nominal composition Nd  Tb  Fe  Co  B  were prepared by various techniques, such as melt-spinning, melt-extraction, splat cooling and mechanically alloying. The Tb and Co content have been found to be crucial in these alloys for achieving high coercivities, up to 500 kA/m. A typical value for the remanence is 1.05}1.10 T. No crystallographic texture was observed, thus, the remanence enhancement was obtained by the spring magnet behavior. The best results have been found when using amorphous precursors and fairly high heating rates during the annealing treatment in an infrared furnace. The amount of Tb could be reduced which yields a lower coercivity but a higher remanence was obtained. TEM and Mo K ssbauer analysis was carried out to determine the volume fraction of soft and hard phases. Optimized magnets contained typically a homogeneous nanocrystalline microstructure of about 50 vol% hard magnetic phase and about 50 vol% soft magnetic -Fe plus (Fe,Co)  B with a narrow grain size distribution. The addition of Si or Nb and Cu improved the microstructure and the magnetic properties. Bonded magnets produced from optimized lean rare-earth magnetic powders show an improved corrosion resistance compared to magnets with higher rare-earth content.  2000 Elsevier Science B.V. All rights reserved. PACS: 61.16.Bg; 61.10.Eq; 61.18.Fs; 75.50.Ww; 81.05.Ys; 81.40.!z Keywords: Lean rare-earth magnetic materials; Remanence enhanced materials; Microstructure; Nanocomposites; Rapid thermal annealing; Hard magnetic RE}Fe-based alloys 0304-8853/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 4 3 5 - 2