Size dependence and interface coupling in antiferromagneticcore/ ferrimagnetic‐shell nanoparticles

E.L. WINKLER; G.C. LAVORATO; E. LIMA JR.; H. E. TROIANI; D. FIORANI; R.D. ZYSLER

Gaithersburg

Conferencia; 9th International Conference on Fine Particle Magnetism (ICFPM2016); 2016

NIST

The use of magnetic nanoparticles in different applications requires the fine control ofthe magnetic anisotropy ofthe system; while the development ofnovel permanent magnets ~nd high density data storage applícations demand highly anisotropic materials, biomedical applications require superparamagnetic nanoparticles at room temperature, The synthesis ofbimagnetic particles combining materials with different magnetic order and anisotropy extend the possibility to design and fabricate new materials with suited properties. In this work we explore the evolution of the magnetic anisotropy as a function of the size of antiferromagnetic CoO core encapsulated in a ferromagnetic CoFe204 shell. The nanoparticles were fabricated by seed-mediated thermal decomposition of acetylacetonates in diphenylether assisted by 01eylamine and oleic acid as surfactants [1]. When the mean size ofthe particles is reduced from 11 nm to 5 nm. \e have found a remarkable in crease of the low temperature coercive field (He) from 21.5 to 30.8 kOe. On the contrary, the mean blocking temperature <TB> decreases from 388 K to 167 K when the size diminishes [2]. We compare the results with the ~10 nm diameter CoO/Zn,Col-xFe204 (x=O-I) core/shell 5~ stem. where the magnetic anisotropy of the shell and the interface interaction are reduced as the .::oncentration of Zn increases. A phenomenological model is used to interpret the interplay among the dífferent competing factors on the magnetic hardening.