Exploring Exchange Bias Coupling in Fe3-O4@CoO Core-Shell Nanoparticle 2D Assemblies

Core-shell ferro(i)magnetic@antiferromagnetic (F(i)M@AFM) nanoparticles exhibiting exchange bias coupling are very promising to push back the superparamagnetic limits. However, their intrinsic magnetic properties can be strongly affected by interparticle interactions. This work reports on the collective properties of Fe3-dO4@CoO core-shell nanoparticles as function of the structure of their assembly. The structure of nanoparticle assembly is controlled by a copper (I) catalyzed alkyne-azide cycloaddition (CuAAC) click reaction between complementary functional groups located at the surface of both substrates and nanoparticles. 2D arrays of nanoparticles with tunable sizes ranging from clusters of few nanoparticles to a dense and homogenous monolayer were prepared. The spatial arrangement of nanoparticles strongly influences the exchange bias coupling which is significantly enhanced for large 2D nanoparticle assemblies and, even more in 3D assemblies such as powder, which favour weak and random dipolar interactions.