The Coercivity-Remanence Synergy in Bulk Nd2fe14b/Α-Fe Nanocomposite Magnet by Crystallizing Amorphous Precursor And Annealing with a Magnetic Field

Abstract

The nanocomposite permanent magnets are regarded as high-performance magnets for prospective applications in sustainable energy technologies. However, coercivity-remanence trade-off leads to severe deterioration of hard magnetic properties. This study introduces an approach to overcome this dilemma. The Fe71.5-xNd7Zr2Nb2.5B17+x (x = 0, 1, 2, 5) bulk magnets are obtained by crystallization of amorphous precursors. In particular, the Nd2Fe14B/a-Fe nanocomposite x = 5 magnet is obtained in which the respective grain size of Nd2Fe14B and a-Fe is 25 nm and 6 nm. Then annealing treatments in a 1 T magnetic field are used to optimize the microstructure and improve magnetic properties of x = 5 magnet. The atom probe tomography (APT) result shows that only non-magnetic intergranular phase is observed in the magnet before magnetic field annealing, while ferromagnetic and non-magnetic intergranular phases are shown after magnetic field annealing. The intrinsic coercivity (Hci) and remanence (Br) of the magnetic field annealed x= 5 magnet are simultaneously increased by 10% and 27%. It leads to the significant increase of maximum energy product ((BH)max) by 55%. The presence of ferromagnetic intergranular phase and the direct contact between soft magnetic a-Fe and hard magnetic Nd2Fe14B can strengthen exchange coupling, leading to the improvement of the Br. The increase of the Hci is due to the increase of concentrations of Nd, Zr, Nb, and B in non-magnetic intergranular phase. Our findings provide a useful strategy to overcome the coercivity-remanence trade-off and subsequently improve hard magnetic properties of nanocomposite magnets.

Keywords: Nanocomposite magnet, Coercivity-remanence trade-off, Intergranular phase, Magnetic field annealing, Atom probe tomography