X-ray Magnetic Circular Dichroism Arising from the Magnetic Dipole Moment in Antiferromagnets

We present a first-principles study of the X-ray magnetic circular dichroism (XMCD) spectra for noncollinear antiferromagnets (AFMs), Mn3Ir and Mn3Sn. By calculating the projected density of states for spin, orbital, and magnetic dipole moments, we evaluated the XMCD spectra for the AFMs. We found that the contributions of the spin magnetic moment almost vanish while those from the magnetic dipole moments give finite XMCD spectra. This indicates that these AFMs are ideal systems to study the XMCD spectra originating from the magnetic dipole moment. By analyzing the magnetic symmetry with and without spin-orbit couplings, we concluded that a symmetry operation that assures a cancellation of spin magnetic moments in the case without spin-orbit couplings is crucial for this feature. We also showed that the spin-orbit couplings for the Mn 3d orbitals have little effect on the shape of the XMCD spectra.