Eur. Phys. J. B (2017) 90: 149
https://doi.org/10.1140/epjb/e2017-70678-6

Regular Article

Ordering and domains in tetragonal crystals of Ising spins coupled via dipolar interactions

Physics Department, Lehman College and Graduate School, The City University of New York, 250 Bedford Park Boulevard West, Bronx, New York, NY 10468-1589, USA

^a e-mail: einschlag@gmail.com

Received: 15 November 2016
Received in final form: 15 February 2017
Published online: 9 August 2017

Abstract

Dipolar coupling in the body-centered tetragonal crystal of Ising spins that is a prototype of the Mn₁₂Ac molecular magnet favors ferromagnetic ordering below the mean-field Curie temperature 0.71 K. With the help of Monte Carlo on crystals of up to one million Mn₁₂ molecules, it is shown that ordering occurs at 0.36 K in elongated crystals. The resulting state is split into ferromagnetic domains with domain walls preferring the diagonal orientation. Domain walls are pinned by the lattice at low temperatures. Making the crystal shorter makes domains finer and smoothens out the singularity at the ordering transition, decreasing the susceptibility in the domain state.