Magnetic Linear X-Ray Dichroism as a Probe of the Magnetocrystalline Anisotropy

We show that for itinerant $3d$ transition metal systems the magnetocrystalline anisotropy energy is directly related to the anisotropic part of the spin-orbit interaction, rather than to the orbital part of the magnetic moment as was previously suggested. We further show how the spin-orbit anisotropy can be obtained by applying the sum rule for magnetic linear dichroism in x-ray absorption. This provides an element specific tool to study metallic multilayer systems displaying novel magnetic properties, such as perpendicular magnetic anisotropy.