Weak anisotropic X-ray magnetic linear dichroism at the Eu M4,5 edges of ferromagnetic EuO(001):: Evidence for 4f-state contributions

We have observed a weak anisotropic x-ray magnetic linear dichroism (AXMLD) at the Eu M(4,5) edges of ferromagnetic EuO(001), which indicates that the 4f states are not rotationally invariant. A quantitative agreement of the AXMLD is obtained with multiplet calculations where the 4f state is split by an effective cubic crystalline electrostatic field. The results indicate that the standard model of rare earths, where 4f electrons are treated as core states, is not correct and that the 4f orbitals contribute weakly to the magnetic anisotropy.