A Note on Stable States of Dipolar Systems at Low Temperatures

In the past several years, many important innovations in nanotechnology were made. Today it becomes possible to make nanosize magnetic particles, and development of high storage-density magnetic device is desired. In such a magnetic particle system, dipole interaction plays the main role. In this note, we consider stable states of dipolar systems at low temperature: Some systems show ``antiferromagnetic structure'', and others show magnetic domain structure, depending on lattice shapes.