Compositional studies and thermal analysis in amorphous and nanocrystalline FePtNbB melt spun ribbons

摘要

The FePtNbB alloys are of interest as a new class of exchange spring magnets. In strictly defined compositional range and after proper conditions of annealing, they develop a microstructure made of small nanograins of hard and soft magnetic phases alternatively disposed and coupled through exchange interactions. Taking advantage of the high uniaxial aniosotropy of the tetragonal hard magnetic FePt phase and high saturation magnetization of the cubic soft magnetic FePt phases, an exchange coupled nanocomposite magnet can be derived. A compositional study of FePtNbB alloys is provided in order to understand the role of each additional element. The possibility of casting alloys where two or more magnetic phases can be obtained is discussed in terms of the eutectic point of the FePt phase diagram. Also, the formation and evolution of the magnetic phases is studied by differential scanning calorimetry (DSC) and detailed analysis of these DSC scans is provided. Activation energy determined from DSC scans provides essential informations about crystallization and disorder-order phase transformation in these alloys.