Spin transition in Gd{sub 3}N-C{sub 80}, detected by low-temperature on-chip SQUID technique

We present a magnetic study of the Gd{sub 3}N-C{sub 80} molecule, consisting of a Gd-trimer via a nitrogen atom, encapsulated in a C{sub 80} cage. This molecular system can be an efficient contrast agent for magnetic resonance imaging (MRI) applications. We used a low-temperature technique able to detect small magnetic signals by placing the sample in the vicinity of an on-chip SQUID. The technique implemented at the National High Magnetic Field Laboratory has the particularity of being able to operate in high magnetic fields of up to 7 T. The Gd{sub 3}N-C{sub 80} shows a paramagnetic behavior and we find a spin transition of the Gd{sub 3}N structure at 1.2 K. We perform quantum mechanical simulations, which indicate that one of the Gd ions changes from a {sup 8}S{sub 7/2} state (L = 0, S = 7/2) to a {sup 7}F{sub 6} state (L = S = 3, J = 6), likely due to a charge transfer between the C{sub 80} cage and the ion.