Micromagnetism simulation on effects of soft phase size on Nd2Fe14B/α–Fe nanocomposite magnet with soft phase imbedded in hard phase**Project supported by the Key Program of the National Natural Science Foundation of China (Grant No. 51331003), the International S & T Cooperation Program of China (Grant No. 2015DFG52020), the General Program of Science and Technology Development Project of Beijing Municipal Education

Abstract

In this study, micromagnetism simulation by using finite difference method is carried out on the Nd2Fe14B/α-Fe nanocomposite magnet with soft phase imbedded in hard phase. The effects of soft magnetic phase size (S) on the magnetic properties and magnetic reversal modes are systematically analyzed. As S increases from 1 nm to 48 nm, the remanence (Jr) increases, while the coercivity (Hci) decreases, leading to the result that the magnetic energy product [(BH)max] first increases slowly, and then decreases rapidly, peaking at S = 24 nm with the (BH)max of 72.9 MGOe (1 MGOe = 7.95775 kJ·m−3). Besides, with the increase of S, the coercivity mechanism of the nanocomposite magnet changes from nucleation to pinning. Furthermore, by observing the magnetic moment evolution in demagnetization process, the magnetic reversal of the soft phase in the nanocomposite magnet can be divided into three modes with the increase of S: coherent rotation (S < 3 nm), quasi-coherent rotation (3 nm ⩽ S < 36 nm), and the vortex-like rotation (S ⩾ 36 nm).