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

Abstract

Abstract The nanoscale distribution of magnetic anisotropies is measured in core@shell MnFe 2 O 4 @CoFe 2 O 4 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) CoFe 2 O 4 hard shell imposes a strong magnetic anisotropy to the otherwise very soft MnFe 2 O 4 core: a large gradient in coercivity is measured inside the MnFe 2 O 4 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).