Optimization of the magnetic properties of aligned Co nanowires/polymer composites for the fabrication of permanent magnets

We aim at combining high coercivity magnetic nanowires in a polymer matrix in a view to fabricate rare-earth free bonded magnets. In particular, our aim is to fabricate anisotropic materials by aligning the wires in the polymer matrix. We have explored the different parameters of the fabrication process in order to produce a material with the best possible magnetic properties. We show that the choice of a proper solvent allows obtaining stable nanowire suspensions. The length and the type of the polymer chains play also an important role. Smaller chains (M-w < 10,000) provide better magnetization results. The magnetic field applied during the casting of the material plays also a role and should be of the order of a fraction of a tesla. The local order of the nanowires in the matrix has been characterized by TEM and small angle X-ray scattering. The correlation between the local order of the wires and the magnetic properties is discussed. Materials with coercivity mu H-0(c) up to 0.70 T at room temperature have been obtained.