Comprehensive understanding of the correlation between structure and harmonic properties of multicore...

Multicore superparamagnetic particles (MCPs) are known to exhibit stronger harmonic signals than monocore superparamagnetic nanoparticles thanks to their superior, dynamic, nonlinear magnetic response. However, a comprehensive understanding of the correlation between MCP structure and harmonic intensity has yet to be achieved. In this study, 14 types of MCPs with different primary and secondary particle sizes were synthesized, and the influence of their structure on their harmonic properties was systematically investigated. As a result, it was found that the intensity of the third harmonic is proportional to the magnetic moment, μ, of the primary particles, and that μ is proportional to N^-1/3 where N is the number of primary particles constituting a single MCP. This correlation holds for MCPs where N > 100 (polycores) but breaks down for MCPs where 1 < N ≤ 100 (oligocores). The optimal structure for maximizing harmonic intensity is predicted to exist near the transition between the oligocore and polycore regions.