Nanopartículas do tipo CoFe2O4@BiFeO3: síntese, caracterização e assinaturas de desordem de spin

Abstract

Nanoscale magnetic systems, such as ferrites, perovskites and core@shell structures, are a group of promising materials, due to their vast technological potential and the possibility of advancing the understanding of fundamental physics related to nanoscale materials. Taking this into account, we synthesize CoFe2O4@BiFeO3 core/shell nanoparticles by coprecipitation and systematically investigate the structural, morphological, and magnetic properties in such nanostructured system. Through structural and morphological characterization, we demonstrate the obtainment of core@shell nanostructure with pure phases. By performing a broad experimental magnetic analysis, we evaluate the magnetic response for the precursor phases, as well as for the core@shell nanostructure. For this latter, we identify fingerprints of the wasp-waisted behavior and exchange bias effect, disclosing the exchange coupling between the phases taking place at the interface. Further, we reveal the exchange coupling between core and shell is strongly affected by a spin glass behavior arisen from the spin disorder in the CoFe2O4@BiFeO3 core/shell nanoparticles. After all, our findings allow us to place the used procedures taking into account the processes of adapted coprecipitation and calcination as a feasible route to the production of high-quality core@shell nanostructures. However, in order not to be bound by a single method, core@shell samples CoFe2O4@BiFeO3 with three core sizes and their precursors were synthesized through hydrothermal synthesis. This second set of samples also showed promising results, as the material obtained showed pure phases for all samples and strong indications of magnetic coupling between the phases that make up the core and the shell, indicating great efficiency of the hydrothermal method.