Orbital magnetism in transition-metal systems: The role of local correlation effects

The influence of correlation effects on the orbital moments for transition metals and their alloys is studied by first-principle relativistic Density Functional Theory in combination with the Dynamical Mean-Field Theory. In contrast to the previous studies based on the orbital polarization corrections we obtain an improved description of the orbital moments for wide range of studied systems as bulk Fe, Co and Ni, Fe-Co disordered alloys and 3d impurities in Au. The proposed scheme can give simultaneously a correct dynamical description of the spectral function as well as static magnetic properties of correlated disordered metals. The growing interest in magnetic materials, their surfaces and nanostructures requires improved theoretical first-principle methods for their description, in particular, when a complex behavior of magnetic properties is observed as in low dimensional systems as, e.g. magnetic clusters, multilayers, thin films and magnetic impurities [1–3]. Their magnetic anisotropies, magneto-optical spectra, magnetic dichroism and other important properties are caused by spin-orbit coupling. While the spin magnetic moments for 3d-transition metals (3d-TM), their alloys and impurities in non-magnetic host are described rather accurately by density functional theory in the local spin-density approximation (LSDA), the orbital moments are systematically underestimated. The reason for this is well-known: the functional variables of the LSDA potential (the charge and spin density) are defined as averages over occupied orbitals. It is natural that such an approximation gives a good description only for the quantities which are slightly dependent on the deviations of orbital occupation numbers from their average, as e.g. spin magnetic moments. An often used approach to improve the description of orbital magnetism is the so-called orbital polarization correction (OP) scheme introduced by Brooks et al. [4–6] in a form of an additional ad hoc term to the Hamiltonian. As it was shown by Ebert and Battocletti [7] the OP enhancement of the orbital moment partially could be realized by utilizing the more general current density functional theory. Analyzing the CDFT Eschrig et al. [8] have derived a systematic expression for the OP correction (for an overview and results of this approach see Ref. [9]). However, despite of a quite accurate description of the orbital moments in pure 3d-TMs and their alloys [10, 11], the LSDA+OP calculations noticeably overestimate