Nanoscale Distribution of Magnetic Anisotropies in Bimagnetic Soft Core–Hard Shell MnFe2O4@CoFe2O4 Nanoparticles

The nanoscale distribution of magnetic anisotropies is measured in core@shell MnFe2O4@CoFe2O4 7.0 nm particles using a combination of element selective magnetic spectroscopies with different probing depths. As this picture is not accessible by any other technique, emergent magnetic properties are revealed. The coercive field is not constant in a whole nanospinel. The very thin (0.5 nm) CoFe2O4 hard shell imposes a strong magnetic anisotropy to the otherwise very soft MnFe2O4 core: a large gradient in coercivity is measured inside the MnFe2O4 core with lower values close to the interface region, while the inner core presents a substantial coercive field (0.54 T) and a very high remnant magnetization (90% of the magnetization at saturation). The nanoscale distribution of magnetic anisotropies inside MnFe2O4@CoFe2O4 nanoparticles is measured using a unique combination of X‐ray magnetic spectroscopies with different probing depths. Coercivity is not constant within a particle. The thin (0.5 nm) hard shell of CoFe2O4 imposes a strong magnetic anisotropy to the soft MnFe2O4 core, which presents a substantial coercive field and a very high remanent magnetization.