Dipolar ordering in Fe8?

We show that the low-temperature physics of molecular nanomagnets, contrary to the prevailing one-molecule picture, must be determined by the long-range magnetic ordering due to many-body dipolar interactions. The calculations here performed, using Ewald's summation, suggest ferromagnetic groundstate with Curie temperature of about 130 mK. The energy of this state is quite close to those of an antiferromagnetic state and to glass of frozen spin chains. The latter may be realized at finite temperature due to its high entropy.