Determination of the Néel vector in rutile altermagnets through x-ray magnetic circular dichroism: The case of MnF2

We present a numerical simulation of x-ray magnetic circular dichroism (XMCD) at the L2,3 edge of Mn in a representative rutile altermagnet MnF2 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 N & eacute;el vector. An exact relationship between the XMCD spectra for different orientations of the N & eacute;el 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 N & eacute;el vector using the XMCD spectra alone.