The role of dipolar interaction in nanocomposite permanent magnets

The effects of dipolar interactions on the magnetization behaviors and magnetic properties of the nanocomposite magnets have been Studied by micromagnetic simulations. Numerical results show that the dipolar interaction plays an important role during the demagnetization process, especially in the magnets with large soft-phase content v(s). For the isotropic nanocomposites, the remanence enhancement can be controlled through adjustments of the grain size D and v(s). However, the appearance of magnetic vortex state leads to a very low remanence in the magnets with large D and v(s). The dependence of coercivity on D and v(s) can be attributed to the exchange-induced magnetization reversal near the grain boundaries and the low nucleation field of soft phase, respectively. For the anisotropic nanocomposites, the reduced remanence m(r) is equal to 1.0 for the magnets with small D or with low v(s). However, in, decreases with increasing us for the magnet with large D due to the influence of dipolar interactions. The difference between the calculated coercivity H-c with and without considering dipolar interaction shows that the dipolar interaction plays a more important role during the magnetization reversal in the soft phase than that in the hard phase. The maximum calculated energy product of the isotropic nanocomposites is only about 40MGOe due to the conflicting relation between remanence and coercivity, while that of the anisotropic nanocomposites is 112MGOe. This reminds us that the alignment of hard grain is important to obtain high performance. (c) 2005 Elsevier B.V. All rights reserved.