Impact of core-shell dipolar interaction on magnetic phases of spherical core-shell nanoparticles

We show that confinement in small volumes affects the interplay of exchange and dipolar interactions and the magnetic phases of hard and soft spherical core-shell nanoparticles. Large variations in the magnetization of thin shells may occur due to the core dipolar field gradient within the shell. The reversal field is tunable by the trends imposed by the dipolar and core-shell interface exchange energies. We show, for instance, that the reversal field of a ${\mathrm{CoFe}}_{2}{\mathrm{O}}_{4}$(30 nm)@${\mathrm{MnFe}}_{2}{\mathrm{O}}_{4}$(6 nm) particle ranges from 15.5 kOe for antiferromagnetic coupling down to 2.5 kOe for ferromagnetic coupling.