Three-dimensional nanomagnetism

N anomagnetism, the scientific field dedicated to the study of nanoscale magnetic objects, has undergone an explosion of activity over the last few decades, driven by fascinating discoveries such as the interaction of magnetization with spin currents (the area of spintronics)1,2 and a wide range of real-world applications3–7. For example, since both the storage and sensing parts of hard disk drives use nanomagnetic structures, the development of nanomagnetism has been a key factor in the vast recent improvements in computer performance and the development of cloud computing. With the exception of some self-assembled systems8,9, nanomagnetism has been mostly confined to two dimensions. In two-dimensional (2D) patterned planar singleor multi-layered magnetic structures, the thickness is of the order of some characteristic magnetic length-scale. This simple geometry leads to monodomain magnetic states in the vertical direction, restricting functionality to the substrate plane (Fig. 1b). In these cases, complex and useful magnetic behaviour is nevertheless possible by exploiting interfacial effects between layers. The maturity now reached in this field10, together with the need for low energy technologies with new functionalities11 and the advent of advanced chemical and self-assembly synthesis techniques capable of growing non-planar nano-objects, make the expansion of nanomagnetism into three dimensions possible (Fig. 1a). In this new paradigm, spin configurations and capabilities extend not only in the plane but also into the vertical direction, and more complex, hierarchical systems leading to new effects can be designed. In this article, we review the state-of-the-art of three-dimensional (3D) nanomagnetism: the new physics associated with different types of 3D magnetic nanostructures, the most promising synthesis and DOI: 10.1038/ncomms15756 OPEN