  The magnetic torque of the antiferromagnetic molecular wheel CsFe8 was
studied down to 50 mK and in fields up to 28 T. Below ca. 0.5 K phase
transitions were observed at the field-induced level-crossings (LCs).
Intermolecular magnetic interactions are very weak excluding an explanation in
terms of field-induced magnetic ordering. A magneto-elastic coupling was
considered. A generic model shows that the wheel structure is unconditionally
unstable at the LCs, and the predicted torque curves explain the essential
features of the data well.
