@@ Magnetic nanoparticles (NPs) represent a critical link between current technology and the next generation of magnetic materials, because of their intriguing physical properties including superparamagnetic behavior. The physics of magnetic NPs is a vivid topic of modern magnetism research. Since it is very difficult to investigate single superparamagnetic nanoparticle in experiment with current technology, a collective system comprised of perfectly-isolated magnetic nanoparticles with uniform size, shape, and interspacing is an ideal research object to reveal the complex magnetism at nanoscale. So there has been a great challenge: controlling the size, shape, and interparticle spacing, and thus dipolar interaction, for each particle even in a dense particle system. Recently, magnetic NPs prepared by chemical synthesis routes generally have a good uniformity and control over size and shape, which can resolve various effects previously obscured by the inhomogeneous broadening due to wide size-distribution or diverse shape and has significantly advanced the studies of nanomagnetism. However, the control on the interspacing of NPs currently by dispersion of NPs in insert media such as SiO2, a polymer matrix, and a liquid suspension, and by self-assembly array is very difficult to completely avoid aggregation in order to obtain isolated NPs and to control well the interparticle spacing.