Spin transition in Gd${}_3$N@C${}_{80}$, detected by low-temperature on-chip SQUID technique

Abstract

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.