Cutaway (micromagnetic) view of spin configurations in a core–shell nanoparticle during a field sweep under FC conditions. Filled circles (green, red, and black) represent magnetic moments in the FM core, ferrimagnetic shell, and core–shell interface, respectively. For simplicity, each ferrimagnetic domain in the shell layer is represented as a spin lattice with a net moment. Dashed lines demarcate the boundaries of crystalline domains within the shell layer, and open circles indicate residual (uncompensated) spins at the surface or domain boundaries.