Most commercial nanoparticles do not possess a single magnetic core but have small magnetic crystals called crystallites. The important question is how these crystallites behave inside a multicore nanoparticle and how they respond to an applied magnetic field. In the Journal of Applied Physics, researchers compare the effective magnetic moments of different multicore nanoparticle systems and shows that they are magnetic-field dependent. The paper’s findings are important for researchers optimizing magnetic nanoparticles for various applications.