Angular dependence and thermal stability of coercivity of Nd-rich Ga-doped Nd-Fe-B sintered magnet

We studied the angular dependence and thermal stability of coercivity of Nd-rich Ga-doped Nd-Fe-B sintered magnets. Experimentally measured angular dependence of coercivity for the as-sintered magnet agrees well with the micromagnetic simulation results for exchange-coupled polycrystalline model that assumes the magnetization reversal is dominated by the domain wall depinning at the grain boundaries. On the other hand, the measured angular dependence of coercivity of the post-sinter annealed sample with an enhanced coercivity deviates from fully exchange-decoupled model in spite of previous experimental results on inter grain exchange decoupling. Based on micromagnetic simulations and Kronmuller equation, it is suggested that the entire elimination of magnetic exchange coupling between Nd2Fe14B grains can further improve the coercivity and its thermal stability of the 5 mu m-grain-sized Dy-free magnet. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.