Phenomenology and Models of Exchange Bias in Core/shell Nanoparticles

Magnetic nanomaterials present new magnetic and transport properties that arise due to a complex interplay between the intrinsic properties of the constituents (such as specifically tailored microstructure and finite size or surface effects) and the interactions among the entities forming them [1]. When reducing the size of magnetic particles to the nanoscale, surface and finite-size effects become fundamental in order to explain their unusual magnetic properties. Moreover, particle surfaces are exposed to environment and are, therefore, easily oxidized, resulting in compound structures with a ferromagnetic core surrounded by an antiferromagnet. When cooling in the presence of a magnetic field the magnetic order established at the shell may result in a pinning of magnetic moments at the interface between the two phases giving rise to the so-called exchange bias (EB) effect [2].