Self-polarization phenomenon and control of dispersion of synthetic antiferromagnetic nanoparticles for biological applications

Using a top-down approach, synthetic antiferromagnetic micro/nanoparticles usable for biological applications were prepared. These particles exhibit “superparamagneticlike” properties. Their magnetic susceptibility can be accurately controlled by the thickness of the constituting layers. When dispersed in solution, striking differences in their interactions are observed depending on their susceptibility. Above a susceptibility threshold, a phenomenon of self-polarization is observed in zero applied field, resulting in a gradual agglomeration of the particles. In contrast, below the susceptibility threshold, the particles get redispersed in zero field. This is interpreted by a self-consistent model taking into account dipolar interactions between particles and their magnetic susceptibility.