Dipolar ordering in crystals of Mn12 Ac

TL;DR

This study investigates the magnetic ordering in Mn12 Ac crystals, revealing that ferromagnetic order is unlikely in elongated crystals and that complex ordering patterns emerge depending on the aspect ratio, challenging traditional methods of determining T_C.

Contribution

It introduces a site-resolved mean-field approach to analyze non-uniform magnetic ordering in elongated Mn12 Ac crystals, showing new ordering behaviors based on aspect ratio.

Findings

Ferromagnetic ordering does not occur in crystals with aspect ratio up to 12.

For aspect ratio around 6, inner and outer regions order differently along the length.

Standard extrapolation methods for T_C are not reliable in this context.

Abstract

Ordering in realistic elongated box-shape crystals of the molecular magnet Mn_12 Ac is investigated with the site-resolved mean-field approximation that does not assume a uniform ordering. It is shown that ferromagnetic ordering should not occur in crystals with the aspect ratio up to 12. Instead, for the aspect ratio about 6, the inner and outer regions of the crystal order in different directions, uniformly along its length. Finding ordering temperature by extrapolating the inverse susceptibility curve does not provide a correct T_C.