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

TL;DR

This study investigates the magnetic properties of Gd$_3$N@C$_{80}$ molecules using a low-temperature on-chip SQUID technique, revealing a spin transition at 1.2 K and potential for MRI contrast applications.

Contribution

The paper demonstrates a novel low-temperature, high-field SQUID method to detect magnetic signals in Gd-based molecules and uncovers a spin transition linked to charge transfer phenomena.

Findings

Gd$_3$N@C$_{80}$ exhibits paramagnetic behavior.

A spin transition occurs at 1.2 K.

Quantum simulations suggest a change in Gd ion states due to charge transfer.

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 $^8S_{7/2}$ state ($L=0, S=7/2$) to a $^7F_{6}$ state ($L=S=3, J=6$), likely due to a charge transfer between the C$_{80}$ cage and the ion.