Synthesis and magnetic properties of Co nanorod superlattices

We present the synthesis and magnetic properties of Co nanorods spontaneously organized in superlattices over a surface of several microns. This material results from the decomposition of a cobalt coordination precursor under hydrogen, in the presence of a long-chain amine and a long-chain acid. This synthetic procedure permits a remarkable control over the size distribution of the nanorods (diameter of 5 nm and controllable mean length from 40 nm to 100 nm). The nanorods are monocrystals, and they are organized side by side along their long axis, in a direction perpendicular to the substrate exposing a surface of tips. Such layers are superposed forming 3D superstructures. These nanorod superlattices are ferromagnetic at r.t. and they are characterized by a strong coercive field as a consequence of their large magnetic anisotropy (magnetocrystalline and shape). Upon application of an external magnetic field the organization is improved even further, and this improvement is partially retained even after field removal. Therefore, this system can be considered as a good candidate for high density magnetic recording.