Ding Sheng Wang

MAGNETOCRYSTALLINE ANISOTROPY OF INTERFACES - FIRST-PRINCIPLES THEORY FOR CO-CU INTERFACE AND INTERPRETATION BY AN EFFECTIVE LIGAND INTERACTION-MODEL

The state tracking method proposed recently is employed for the first-principles local density determination of interface magnetocrystalline anisotropy (MCA) energy by the full potential linearized augmented plane wave method. The interface MCA mechanism involving Co is studied with the Co-Cu interface as an example. The free standing Co monolayer is found to exhibit a strong negative MCA (easy axis in the layer plane), -1.35 meV, due to the spin-orbit coupling between spin-down bonding z(2) and anti-bonding xz or yz states along in the Brillouin zone, and between anti-bonding z(2) and bonding xz and yz states near (M) over bar. At the Co-Cu interface, the out-of-plane Co bonding z(2), xz and yz states interact strongly with the Cu states, giving rise to the main change: a decrease in the magnitude of this negative contribution. Together with the effect of changes in band filling and the contribution from the spin-orbit coupling between opposite spins, the interface MCA energy of a Co layer is -0.38 meV for a Co overlayer on a Cu(001) substrate, and near zero (- 0.01 meV) for a Co layer sandwiched between a Cu(001) matrix. These results are in very good agreement with recent in situ experimental measurements. An effective ligand interaction model is developed which successfully interprets the first principles results and further shows how the interface MCA depends on the energy of the d orbitals of the interface atoms and the strength of the interface bonds.

Magnetism of surfaces and interfaces

Recent experimental advances in the study of surfaces have raised important questions about our fundamental understanding of these phenomena. One important consequence of this has been the development of theoretical/computational methods for accurately determining the electronic structure and properties of surfaces and interfaces. This talk reports on theoretical determinations of the magnetic properties of free surfaces [e.g., Ni(110)] and overlayers [e.g., Ni on Cu(001)] based on self‐consistent spin polarized energy band determinations of the energy dispersion and spatial character of surface states. Particular attention is paid to surface state effects on surface spin polarization, magnetic moments, and exchange splittings. Detailed results of charge and spin densities and layer projected density of states are presented. Comparisons are made to relevant photo‐emission and other experiments, the nonexistence of magnetically ’’dead’’ layers is described, and comparisons with earlier results1 on coherent modulated Cu/Ni structures are given.

Magnetism at surfaces and interfaces

Abstract The current state-of-the-art of ab-initio calculations of the magnetic structures of surfaces and interfaces is highlighted by presenting results obtained with the recently developed full-potential linearized augmented plane wave method for thin films. In particular, spin density maps, (induced) magnetic moments and hyperfine-fields are presented for the clean metal surfaces Fe(001), Ni(001) and Pt(001). The magnetic moments on an interface are discussed for the prototypical case Ni/Cu.

Local spin‐density theory of interface and surface magnetocrystalline anisotropy: Pd/Co/Pd(001) and Cu/Co/Cu(001) sandwiches

The interface magnetocrystalline anisotropy (MCA) of Cu/Co/Cu(001) and Pd/Co/Pd(001) sandwiches are investigated, employing our recently developed state tracking approach based on the full potential linearized augmented plane wave energy band method. The strong negative MCA energy for the Co monolayer is found to be decreased for Co/Cu, and even becomes positive for Co/Pd due to the interfacial hybridization, which reduces the spin orbit coupling (SOC) between the dxz,yz − dz2 pair at M.

All-electron self-consistent determination of spin-polarization and knight shift of A Pt(001)film

Abstract Theoretical Knight shift distributions for a thin Pt(001) film show a decreased magnetic susceptibility at the surface (and hence a decrease in the magnitude of the negative core polarization) but an increased positive valence contribution resulting in a positive Knight shift at the surface in agreement with NMR results on small Pt particles.

First principles determination of spin-orbit induced phenomena at surfaces, interfaces and superlattices: magnetocrystalline anisotropy and magnetic circular dichroism

Abstract Two spin-orbit coupling induced effects, namely magnetocrystalline anisotropy (MCA) and magnetic circular dichroism (MCD) have been investigated using the first principles full potential linearized augmented plane wave method. For MCA, the stable results obtained through our newly developed state tracking approach for free standing Fe and Co monolayers, CoCu and CuPd interfaces and CoCu superlattices can be related and explained in terms of more fundamental electronic properties such as bonding character and band structure. From the directly calculated MCD spectra and ground state properties (e.g., spin and orbital magnetic moments), we found that the MCD orbital sum rule works well for transition metal systems, while its spin counterpart may result in significant errors.

Electronic structure and magnetism of surfaces, interfaces and modulated structures (superlattices)

Recent developments in the study of surfaces and interfaces of metals and of artificial materials such as bimetallic sandwiches and modulated structures are described. Key questions include the effects on magnetism of reduced dimensionality and the possibility of magnetically “dead” layers. These developments have stimulated an intensified theoretical effort to investigate and describe the electronic and magnetic structure of surfaces and interfaces. One notable success has been the development of a highly accurate full-potential all-electron method (the FLAPW method) for solving the local spin density equations self-consistently for a single slab geometry. We describe here this advanced state of ab initio calculations in determining the magnetic properties of transition metal surfaces such as those of the ferromagnetic metals Ni(001) and Fe(001) and the Ni/Cu(001) interface. For both clean Fe and Ni(001) we find an enhancement of the magnetic moments in the surface layer. The magnetism of surface and interface Ni layers on Cu(001) (no “dead” layers are found) is described and compared to the clean Ni(001) results. Finally, the role ofμSR experiments in answering some of the questions raised in these studies will be discussed.