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Abstract The attraction between unequally sized like magnetic poles is characterized herein. Finite element analysis (FEA) simulation has verified that attraction can occur between like poles. Between two unequally sized like poles with various dimensions and alignments, a turning point (TP) appears on the curves of force vs. distance between them, which is caused by the localized demagnetization (LD). The LD plays a role far before the distance between the poles reduces to the TP. The LD area may have a changed polarity, making the attraction possible and not in violation of basic laws of magnetism. Here, the LD levels have been determined using FEA simulation, and the factors affecting the LD have been explored, including the geometry, the linearity of the BH curve, and the alignment of the magnet pairs. Novel devices can be designed with attraction between the centers of such like poles and repulsion when off-center.

Abstract This investigation reveals the mystery of the cases where magnetic like poles attract each other, and unlike poles repel one another. It is identified that for two unequally sized like poles, the pole with a higher P c (permeance coefficient) causes a localized demagnetization (LD) to the pole with a lower P c . If the LD is large enough, the polarity of a localized area can be reversed, resulting in an attraction between these two like poles in the LD area in a small gap. Two unusual behaviors are observed: (1) an inflection point IP appears on the force vs gap curves of all the unequally sized like poles since they have different P c . Normally, the like poles’ repelling force increases when the gap decreases, but this IP results in nonmonotonic curves, even an attractive force in a small gap; (2) for some NdFeB magnets with a low coercivity and nonlinear B–H curve in the 2nd quadrant, a repulsion can occur for these unequal sized unlike poles, after previously pairing with their like poles that left an unrecoverable LD and reversed polarity area. The relationship of the LD, the P c ratio, and the B–H curve are also explored in this paper.