Exchange-coupled bimagnetic cobalt/ iron oxide branched nanocrystal heterostructures

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 singte-crystal tetrapod-shaped skeletoπ of ferrimagnetic (FiM) iron oxide functionalized with multiple polycrystalline spherícal domains of ferromagnetic (FM) Co. Due to the direct bonding interfaces formed between the two materίals at the relevant junction regions, the HNCs exhibft 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 ratίonal design of nanoheterostructures potentially exploitable as active elements in future generations of magnetic recording devices.