We present a magnetic study of the Gd 3 N@C 80 molecule, consisting of a Gd-trimer via a Nitrogen atom, encapsulated in a C 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 NHMFL has the particularity to operate in high magnetic fields of up to 7 T. The Gd 3 N@C 80 shows a paramagnetic behavior and we find a spin transition of the Gd 3 N structure at 1.2 K. We perform quantum mechanical simulations, which indicate that one of the Gd ions changes from a 8 S 7/2 state (L = 0, S = 7/2) to a 7 F 6 state (L = S = 3, J = 6), likely due to a charge transfer between the C 80 cage and the ion.