Competitive Size Effects in Antiferromagnetic|Ferrimagnetic Core|Shell Nanoparticles for Large Exchange Bias

A family of exchange-coupled core−shell (CS) nanoparticles composed of an antiferromagnetic (AFM) core (Co0.3Fe0.7O) and a ferrimagnetic (FiM) shell (Co0.6Fe2.4O4) was investigated to unravel the role played by the dimension of the two components on the magnetic properties of the system. The series comprises three samples with different core diameters (2, 5, and 16 nm) and fixed shell thickness of ∼2 nm. Although a strong core and shell magnetic coupling occurs in all the samples, the final properties of the hybrid nanosystems are greatly influenced by the size of the two counterparts. These findings highlight the significant influence of the size of the AFM and FiM components on the hybrid system’s ultimate properties. This result is potentially relevant for defining the working conditions of nanodevices exploiting exchange-bias phenomena, which have been recently proposed in the literature for application in several technological fields, ranging from rare-earth free magnets, spintronics, optoelectronics, and magnetic-refrigeration.