Observation of the influence of dipolar and spin frustration effects on the magnetocaloric properties of a trigonal prismatic {Gd-7} molecular nanomagnet

We report the synthesis and structure of a molecular {Gd-7} cage of the formula ((Pr2NH2)-Pr-i)(6)[Gd-7(mu(3)-OH)(3)(CO3)(6)((O2CBu)-Bu-t)(12)] which has crystallographic C-3h symmetry. Low temperature specific heat and adiabatic demagnetization experiments (the latter achieving temperatures below 100 mK), lead to the observation of the effects of both intramolecular dipolar interactions and geometric spin frustration. The dipolar interaction leads to a massive rearrangement of energy levels such that specific heat and entropy below 2 K are strongly modified while magnetic susceptibility and magnetization above 2 K are not affected. The consequences of these phenomena for low temperature magnetocaloric applications are discussed.