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A colloidal seeded-growth strategy, relying on time-programmed delivery of selected stabilizing surfactants, has been developed to synthesize bimagnetic hybrid nanocrystals (HNCs) that consist of a single-crystal tetrapod-shaped skeleton of ferrimagnetic (FiM) iron oxide functionalized with multiple polycrystalline spherical domains of ferromagnetic (FM) Co. Due to the direct bonding interfaces formed between the two materials at the relevant junction regions, the HNCs exhibit FiM-FM exchange coupling, which transcribes into a rich scenario of significantly modified properties (not otherwise achievable with any of the single components or with their physical mixtures), including higher saturation magnetization and coercitivity values, exchange biasing, and enhanced thermal stability due to induced extra anisotropy. The availability of these new types of HNCs suggests that development of appropriate synthetic tools for arranging distinct material domains in predetermined spatial arrangements could lead to a more rational design of nanoheterostructures potentially exploitable as active elements in future generations of magnetic recording devices.

In this work, recent achievements of nanochemistry research in the fabrication of colloidal nanoheterostructures are reviewed through revisiting relevant papers and related patents. Attention is focused on newly conceived generations of hybrid nanocrystals (HNCs) with a topologically controlled composition, in which size and shape tailored domains of different inorganic materials are permanently assembled together in a single multifunctional particle. Strategies for accessing HNCs in various configurations, such as core/shell systems, hetero-oligomers based on nearly spherical portions, and highly asymmetric nanostructures comprising joint sections with different shapes, are discussed. The chemical-physical properties and technological advantages offered by such complex nanocrystals are also highlighted.