Spin-enhanced Magnetocaloric Effect in Molecular Nanomagnets

Unprecedentedly large magnetocaloric effect for the temperature region below 10~K is found for the Fe$_{14}$ molecular nanomagnet [Angew. Chem. Int. Ed. {\bf 42}, 3781 (2003)]. We show that this comes out from a combination of several features, such as the spin ground-state that amounting to $S=25 $ is amongst the highest ever reported, and the highly symmetric cluster core that results in small cluster magnetic anisotropy. The latter enables the occurrence of long-range magnetic order below $T_{N}=1.87$~K, probably of antiferromagnetic nature. We also show that low-lying excited $S$ states additionally enhance the MCE of Fe$_{14}$. For these reasons, Fe$_{14}$ has therefore high potentiality to work as low-temperature magnetic refrigerant.