Control of the effective magnetic anisotropy by interface coupling in Fe3O4-core/Co1-xZnxFe2O4-shell nanoparticles

F. FABRIS; E. LIMA JR.; R.D. ZYSLER; E.L. WINKLER

S.C. de Bariloche

Simposio; XXIII Latin American Symposium on Solid State Physics (XXIII SLAFES); 2018

SLAFES

The use of magnetic nanoparticles in dierent applications requires the ne control of the magnetic anisotropy of the system; while the development of novel permanent magnet and high density data storage demand highly anisotropic materials, biomedicalapplications require superparamagnetic nanoparticles at room temperature. The fabrication of bimagnetic systems allows to combining materials with dierent magnetic order and anisotropy, and it extends the possibility of design new materials with suited properties. In this work we explore the evolution of the magnetic anisotropy of exchange coupled core/shell system as a function of the shell composition. The nanoparticles are constituted by a ~6 nm Fe3O4 core encapsulated in a 2 nm-thick Co1-xZnxFe2O4 (x = 0-1) ferrimagnetic (FiM) shell. The nanoparticles were fabricated by seed-mediated thermal descomposition of acetylacetonates in diphenylether assisted by oleylamine and oleic acid as surfactants. The system presents an enhancement of the coercivity eld (HC) and thermal stability as compared to its FiM single-phase counterpart. The coercivity and the blocked temperature increase monotonically when the Zn concentration decrease from HC 0.18 kOe and <TB >~18 K for x = 1 to HC ~7 kOe and <TB >~170 K for x = 0. We found that the eective magnetic anisotropy of the system can be tuned by replacing Co2+ with Zn2+ ions in the shell, providing a new approach to tune the magnetic properties and to design novel hybrid nanostructures. A phenomenological model is used to interpret the interplay among the dierent competing factors on the magnetic hardening.