Nature produces ferromagnetic materials based on nearest neighbor exchange interaction between atomic spins. For artificially fabricated nanomagnets, it is those “small” magnetic energies, e.g. anisotropy, dipolar interaction and indirect exchange interaction that play crucial roles against the thermal fluctuation. We have developed strong capabilities to grow nanodot assemblies in ultrahigh vacuum with controllable size and density on/in both metallic and insulating templates. Based on our novel synthesis capability, we have studied artificial nanomagnets with tunable coupling strength via dimensionality control of the mediating electrons in one-dimensional (1-D), 2-D, and 3-D. We show that such kind of dimensional confinement provides a unique way to induce novel magnetic properties and to gain control of them. The research outlined in this work provides the science base to understand, modify, and manipulate the magnetic properties through dimensional confinement.