Low dipolar interactions in dense aggregates of aligned magnetic nanowires

Magnetic interactions in aggregates of polyol-synthesized cobalt nanowires are studied by δM plots. Negative δM values are obtained as expected for magnetostatic coupling between physically isolated nanowires, without exchange interactions. Very weak interactions (down to δM = −0.05) are achieved by alignment and dispersion into polymeric matrices. We attribute this to the fact that during the fabrication of the composite materials, the nanowires reorganize so as to minimize the dipolar interactions. Since the δM-plots are sensitive to the nature of the demagnetized state, it is shown by micromagnetic simulations that the ac demagnetized state provides the best choice of a starting point since it ensures that macroscopic configurations consisting of single domain states of each wire are compared. The low interactions observed in these materials suggest that these composite materials are candidates for rare-earth free permanent magnets since demagnetization phenomena are minimized.