Magnetic circular x-ray dichroism in transverse geometry: Importance of noncollinear ground state moments

The orbital and spin magnetic moment and the magnetic dipole term of $3d$ transition metals are no longer collinear when the electron spins are forced out of the easy direction by an external magnetic field. This effect provides a simple way to measure with magnetic x-ray dichroism the anisotropy of the orbital magnetic moment and the magnetic dipole term in a geometry where the contribution of the spin magnetic moment disappears, i.e., with the photon helicity vector perpendicular to the magnetization direction.