Preparation of nanocrystalline Mn-Al-C magnets by melt spinning and subsequent heat treatments

Mn54Al44C2 ribbon samples have been prepared by melt spinning in a single-phase epsilon hexagonal disordered state and its exothermal transformation at around 500 degrees C into a tetragonal L1(0) type magnetic structure (tau-phase) was followed by DTA, DSC, X-ray diffraction and thermomagnetic measurements. The metastable T-phase stabilized by carbon addition could be transformed reversibly into the epsilon-phase at around 800 degrees C, without decomposition into the stable Al8Mn5 and beta manganese phases. The almost constant Curie temperature obtained for partially transformed two-phase samples indicated a compositionally invariant transformation. By grinding the thin (25 mu m) ribbon into sub-millimeter flakes, a bulk anisotropic magnet could be compacted by magnetic field oriented powder technology. (C) 2006 Elsevier B.V. All rights reserved.