Partitioning of Tb and Dy at the liquid/Nd₂Fe₁₄B interface in Nd–Fe–B magnets: Insights from single crystal growth

Heavy rare earth elements (HREE) such as dysprosium (Dy) and terbium (Tb) are added to Nd-Fe-B permanent magnets to increase their coercivity. However, optimizing both the content and distribution of HREE requires a thorough understanding of the thermodynamic equilibria at the interfaces between the τ 1 -phase grains and the liquid phase that forms during grain boundary diffusion or powder mixing processes. In this study, we synthesized τ 1 -phase single crystals using the flux growth method with Nd-HREE-Fe-B flux alloys containing various HREE concentrations. Following the crystal growth, phase separation was performed by centrifugation. The composition of the τ 1 single crystals was analyzed by wavelength dispersive spectroscopy (WDS), while the liquid phase was characterized by inductively coupled plasma (ICP) spectroscopy. The partitioning laws of HREE between the τ 1 phase and the equilibrium liquid phase were determined, providing valuable insights into the optimisation of HREE content in Nd-Fe-B magnets. • Detailed methodology for the growth of (Nd,HREE)₂Fe₁₄B large single crystals • Chemical analysis of (Nd,HREE)₂Fe₁₄B single crystals and the coexisting equilibrium liquid phase • Partitioning laws of HREE (Tb or Dy) between the liquid and Nd₂Fe₁₄B phases