https://doi.org/10.1007/s100510050808
Order by thermal disorder in 2D planar rotator model with dipolar interactions
Dipartimento di Fisica dell' Università, and Istituto Nazionale per la Fisica della
Materia, Via delle Scienze, 43100 Parma, Italy
Corresponding author: a rastelli@pr.infn.it
Received:
4
August
1998
Published online: 15 June 1999
The energy of a square planar rotator model of spins interacting
via dipolar forces is minimized by infinite inequivalent
configurations corresponding to spins arranged on four
interpenetrating sublattices making angles α, 
,
, 
with a reference axis, α being
arbitrary. This infinite degeneracy of the ground state is
accidental in nature and one expects that it is removed by
thermal fluctuations in agreement with Monte Carlo simulation.
Indeed we find that the elementary excitation energies which
depend on α lead to a free energy which is a function of
α with minima at 
and 
corresponding to columnar configurations. This selection of
columnar configurations out of the infinite ground state manifold
is an example of order by thermal disorder.
PACS: 75.10.Hk – Classical spin models / 75.30.Ds – Spin waves
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 1999
