We present a numerical simulation of x-ray magnetic circular dichroism (XMCD) at the $L_{2,3}$ edge of Mn in a representative rutile altermagnet ${\mathrm{MnF}}_2$ using a combination of density functional theory plus exact diagonalization of the atomic model. We explore how the dichroic spectra vary with the orientation of the light propagation vector and the Néel vector. An exact relationship between the XMCD spectra for different orientations of the Néel vector, valid in the absence of the valence spin-orbit coupling and core-valence multipole interaction, is derived and its approximate validity for the full Hamiltonian verified by numerical calculation. This relationship allows one to determine the in-plane orientation of the Néel vector using the XMCD spectra alone.

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• Magneto-optical effect
• Altermagnets
• Crystal-field theory
• X-ray magnetic circular dichroism