Tuning the magnetic anisotropy and magnetotransport of self-assemblies of exchange coupled core/shell nanoparticles

F. FABRIS; E. LIMA JR.; C. QUINTEROS; L. NEÑER; M. GRANADA; M. SIRENA; R.D. ZYSLER; H.E. TROIANI; V. LEBORÁN; F. RIVADULLA; E.L. WINKLER

Gijón

Congreso; International Conference on Fine Particle Magnetism (ICFPM19); 2019

International Conference on Fine Particle Magnetism (ICFPM19)

The use of magnetic nanoparticles in different applications requires the fine control of the magnetic anisotropy of the system; while the development of novel permanent magnet and high density data storage demand hard magnetic materials, biomedical applications require superparamagnetic nanoparticles at room temperature. The fabrication of bimagnetic nanoparticles allows to combining materials with different magnetic order and anisotropy, and it extends the possibility of design new materials with suited properties. The core/shell structure also permit to combining different functionalities in a single nanoparticle as a magnetic conductor cores encapsulated with an insulator material. This possibility, together with the ability to form large areas of self-assembled nanoparticles, allows envisage future tunnel magnetotransport devices based on nanoparticles. Given that the anisotropy of the system is to a great extent responsible of the switching field of the tunnel magnetoresistance, assemblies of core/shell nanoparticles provides an ideal system to studying the spin-dependent transport between magnetic nanoparticles and also provides a tool to control the magnetoresistive response by tuning of the coercivity field of the magnetic nanoparticles.With this motivation we design and fabricate exchange coupled core/shell bimagnetic systems and study the evolution of the magnetic anisotropy of as a function of the shell composition. We  synthesized, by high temperature thermal decomposition route, ~9.5 nm nanoparticles systems formed by a FiM half-metallic Fe3O4 core, encapsulated with a Co1−xZnxFe2O4 (x = 0?1) shell. Then large areas of Fe3O4/Co1−xZnxFe2O4 self-assembled nanoparticles were produced to develop magnetoresistive nanostructures. The results show that progressive replacement of Co2+ by Zn2+ in the shell reduces the magnetic anisotropy of the system and shifts the maximum of the tunnel magnetoresistance of the self-assembled nanostructure in a perfect correlation with the magnetic response. These results demonstrate the feasibility of tuning the tunnel magnetoresistance switching field in self-assembled core/shell nanoparticles, given a promising base for the application of nanoparticles in futures spintronic devices.