# Determination of Magnetic Anisotropy Tensors in Actinide Complexes Using Torque Magnetometry: A U(IV) Case Study

## TL;DR

This study uses torque magnetometry to determine the magnetic properties of a uranium complex, offering insights into actinide magnetism.

## Contribution

First application of cantilever torque magnetometry to an actinide-based molecular system.

## Key findings

- Magnetic anisotropy axes of U(DOTA)(H2O) align with those of Pr3+ and Dy3+ analogues.
- Cantilever torque magnetometry combined with calculations describes the non-Kramers ground state of U(DOTA)(H2O).
- Results validate computational approaches for 5f-element magnetism.

## Abstract

In this study, we
employed cantilever torque magnetometry
to probe
the magnetic anisotropy of a single crystal of U­(DOTA)­(H2O) (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid),
representing, to the best of our knowledge, the first application
of this technique to an actinide-based molecular system. Combining
cantilever torque magnetometry data with ab initio calculations allowed us to determine the magnetic anisotropy tensor
of the uranium center. The resulting parameters enabled direct comparison
with the isoelectronic lanthanide complex previously reported in the
literature as well as with ab initio predictions
for the theoretical Es4+ isostructural analogue. We find
that the magnetic anisotropy axes of U­(DOTA)­(H2O) (5f
2) closely align with those of the
Pr3+ (4f
2) and Dy3+ (4f
9) analogues and with those predicted
for Es­(DOTA)­(H2O) (5f
9). The combination of CTM and electronic structure calculations
was essential to describe the weakly paramagnetic, EPR-silent, non-Kramers
ground state of U­(DOTA)­(H2O), despite the
added complexity of four noncollinear molecules in the unit cell.
Overall, these results demonstrate that cantilever torque magnetometry
provides a powerful route to characterize the magnetic anisotropy
of actinide complexes and offers a valuable experimental benchmark
for validating computational approaches to 5f-element magnetism.