Speaker
Description
X-ray magnetic circular dichroism (XMCD) is a well-established technique for investigating magnetism. Here, we present theoretical studies of XMCD at the manganese L$_{2,3}$ edge in two altermagnets, MnTe [1] and MnF$_2$ [2], with experimental data available for MnTe. Our calculations reveal that spin-orbit coupling in the valence states has a negligible effect on the XMCD spectra. In other words, the spectra computed in an idealized non-relativistic system—where altermagnetism is well-defined by symmetry—closely resemble those obtained in a more realistic model that includes valence spin-orbit coupling. This feature distinguishes XMCD from optical or transport measurements, where spin-orbit coupling is essential for observing magneto-optical or anomalous Hall effects. Using MnTe and MnF$_2$ as examples, we demonstrate that crystal symmetry dictates the origin of the finite XMCD signal, with different terms in the Hamiltonian contributing depending on symmetry. In the case of rutile MnF$_2$, the core-valence exchange interaction causes a minor modification of the XMCD signal, which exists even without this interaction. Conversely, in hexagonal MnTe, the core-valence interaction is necessary to observe any finite XMCD signal at all. These distinct origins of XMCD account for the different magnitudes of the effect in these isolectronic materials (Mn $d^5$). Finally, we will discuss how XMCD can be utilized to determine the orientation of the Néel vector.
References
[1] A. Hariki et al., Phys. Rev. Lett. 132, 17670 (2024).
[2] A. Hariki et al., Phys. Rev. B 110, L100402 (2024).
