### Abstract

By means of the molecular dynamics simulation of gradual cooling processes, we investigate magnetic properties of classical spin systems only with the magnetic dipole-dipole interaction, which we call dipolar systems. Focusing on their finite-size effect, particularly their boundary geometry dependence, we study two finite dipolar squares cut out from a square lattice with Φ = 0 and π/4, where Φ is the angle between the direction of the lattice axis and that of the square boundary. Distinctly different results are obtained in the two dipolar squares. In the Φ = 0 square, the "from-edge-to- interior freezing" of spins is observed. Its ground state has a multidomain structure whose domains consist of two among infinitely (continuously) degenerated Luttinger-Tisza (LT) ground-state orders on a bulk square lattice, i.e., the two antiferromagnetically aligned ferromagnetic chains (af-FMC) orders directed parallel to the two lattice axes. In the Φ = π/4 square, on the other hand, the freezing starts from the interior of the square, and its ground state is nearly in a single domain with one of the two af-FMC orders. These geometry effects are argued to originate from the anisotropic nature of the dipole-dipole interaction, which depends on the relative direction of sites in the real space of the interacting spins.

Original language | English |
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Article number | 044705 |

Journal | Journal of the Physical Society of Japan |

Volume | 76 |

Issue number | 4 |

DOIs | |

Publication status | Published - 2007 Apr |

Externally published | Yes |

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### Keywords

- Dipole-dipole interaction
- Freezing characteristics
- Magnetic nano-particle array
- Molecular dynamics simulation

### ASJC Scopus subject areas

- Physics and Astronomy(all)

### Cite this

*Journal of the Physical Society of Japan*,

*76*(4), [044705]. https://doi.org/10.1143/JPSJ.76.044705