# Zeeman interaction and Jahn-Teller effect in $\Gamma_8$ multiplet

## TL;DR

This paper analyzes how the Zeeman interaction and Jahn-Teller effect influence the magnetic properties of the $ ext{ extGamma}_8$ multiplet, combining theory with ab initio calculations to explain experimental observations and predict effects in specific ions.

## Contribution

It provides a comprehensive theoretical framework for understanding the interplay of magnetic moments and Jahn-Teller effects in cubic multiplets, supported by ab initio calculations.

## Key findings

- Zeeman interaction remains isotropic with dynamical Jahn-Teller effect.
- Static Jahn-Teller distortion can change the sign of $g$ factors.
- Ab initio calculations match experimental $g$ factors for Np$^{4+}$ and predict strong Jahn-Teller effects in Ir$^{4+}$.

## Abstract

We present a thorough analysis of the interplay of magnetic moment and the Jahn-Teller effect in the $\Gamma_8$ cubic multiplet. We find that in the presence of dynamical Jahn-Teller effect, the Zeeman interaction remains isotropic, whereas the $g$ and $G$ factors can change their signs. The static Jahn-Teller distortion also can change the sign of these $g$ factors as well as the nature of the magnetic anisotropy. Combining the theory with state-of-the-art {\it ab initio} calculations, we analyzed the magnetic properties of Np$^{4+}$ and Ir$^{4+}$ impurity ions in cubic environment. The calculated $g$ factors of Np$^{4+}$ impurity agree well with experimental data. The {\it ab initio} calculation predicts strong Jahn-Teller effect in Ir$^{4+}$ ion in cubic environment and the strong vibronic reduction of $g$ and $G$ factors.