Exchange-Coupled Bimagnetic Core–Shell Nanoparticles for Enhancing the Effective Magnetic Anisotropy

Abstract

Magnetic nanoparticles offer enormous possibilities of controlling the properties of magnetic materials due to their size and surface effects, including superparamagnetism, surface spin disorder, and surface anisotropy. Recently, the design and fabrication of novel materials based on bimagnetic nanoparticles provided novel strategies by incorporating interface effects. Therefore, the hysteretic behavior and the thermal stability of the magnetic moments can be tuned by controlling their composition, size, morphology, and interactions. This chapter focuses on the enhancement of the magnetic anisotropy due to the exchange coupling in bimagnetic nanoparticles synthesized by chemical colloidal methods. Various types of exchange-coupled bimagnetic nanoparticle systems are presented, and the different magnetization-reversal mechanisms are briefly discussed. Then, key aspects of the synthesis methods for obtaining core–shell nanoparticles are described, focusing on the heat-up thermal decomposition method. Finally, the anisotropy enhancement in antiferromagnetic/ferrimagnetic CoO-core/CoFe2O4-shell nanoparticles is presented and discussed as a case study.