Micromagnetism simulation on effects of soft phase size on Nd₂Fe₁₄B/α–Fe nanocomposite magnet with soft phase imbedded in hard phase

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 (J _r) increases, while the coercivity (H _ci) 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). (paper)