Nonconventional screening of the Coulomb interaction in FexOy clusters: An ab-initio study

From microscopic point-dipole model calculations of the screening of the Coulomb interaction in non-polar systems by polarizable atoms, it is known that screening strongly depends on dimensionality. For example, in one dimensional systems the short range interaction is screened, while the long range interaction is anti-screened. This anti-screening is also observed in some zero dimensional structures, i.e. molecular systems. By means of ab-initio calculations in conjunction with the random-phase approximation (RPA) within the FLAPW method we study screening of the Coulomb interaction in FexOy clusters. For completeness these results are compared with their bulk counterpart magnetite. It appears that the onsite Coulomb interaction is very well screened both in the clusters and bulk. On the other hand for the intersite Coulomb interaction the important observation is made that it is almost contant throughout the clusters, while for the bulk it is almost completely screened. More precisely and interestingly, in the clusters anti-screening is observed by means of ab-initio calculations

Island-assisted interface alloying and magnetic polarization at submonolayer V/Cr(001) interfaces

Island-assisted interface alloying was observed during submonolayer deposition on Cr(001) substrates at 525 K. Scanning tunneling spectroscopy suggests atomic interchange at the center of the islands during the early stages of growth, giving rise to a Cr core in the center of the island and a gradually increasing V concentration toward the island rim. The existence of a VCr alloy with equiatomic composition is concluded by comparing tunneling spectra measured at the island rim with density-functional theory calculations. Coalescence of the initial islands gives rise to inhomogeneous alloying at monolayer coverage. Antiferromagnetic coupling between the islands and the Cr(001) substrate is found for coverages up to 0.50 atomic layers. At higher coverages, no magnetic contrast was observed

Ab-initio Rechnungen zum Zusammenhang zwischen Magnetismus und Struktur ultraduenner Filme

This work presents a study of the ground-state atomic and magnetic structure of unsupported 3d transition-metal monolayers (UML). We performed total energy calculations on the basis of the density functional theory in the local spin-density approximation (LSDA) using the full-potential linearized augmented-plane wave method (FLAPW) in film geometry as a function of the lattice parameters, crystal structure, and magnetic order. The atoms are arranged in a two-dimensional (2D) square lattice or in a (2D) hexagonal lattice and we included nonmagnetic, p(1 x 1)-ferromagnetic and c(2 x 2)-antiferromagnetic structures. Antiferromagnetism on a hexagonal lattice leads to noncollinear spin-configurations, which we approximated by a c(2 x 2)-antiferromagnetic structure on a centered rectangular lattice. The results are summarized in a structure table. The UMLs at the beginning of the 3d-series (Ti, V) are nonmagnetic and crystallize in the closed packed hexagonal structure; Fe, Co and Ni are hexagonal with a ferromagnetic ground-state spin-structure. In the middle of the 3d-series Mn and Cr are antiferromagnetic and there is a strong competition between the hexagonal and the square lattice: The ground-state found for Mn is hexagonal and for Cr quadratic. The ground-state lattice constants of 2D-magnets are found to be generally smaller than those of the bulk materials. A distinct magneto-volume effect was found, with a maximum volume expansion for hexagonal Mn (12%). (orig.)Available from TIB Hannover: RA 831(3364) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Island-assisted interface alloying and magnetic polarization at submonolayer V/Cr(001) interfaces

Island-assisted interface alloying was observed during submonolayer deposition on Cr(001) substrates at 525 K. Scanning tunneling spectroscopy suggests atomic interchange at the center of the islands during the early stages of growth, giving rise to a Cr core in the center of the island and a gradually increasing V concentration toward the island rim. The existence of a VCr alloy with equiatomic composition is concluded by comparing tunneling spectra measured at the island rim with density-functional theory calculations. Coalescence of the initial islands gives rise to inhomogeneous alloying at monolayer coverage. Antiferromagnetic coupling between the islands and the Cr(001) substrate is found for coverages up to 0.50 atomic layers. At higher coverages, no magnetic contrast was observed

First principles calculations of the electronic structure of magnetic overlayers on transition metal surfaces

SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Fundamentals of nanoelectronics Lectures

SIGLEAvailable from TIB Hannover: RR 9223(14) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Skyrmion-antiskyrmion pair creation and annihilation in a cubic chiral magnet

A fundamental property of particles and antiparticles (such as electrons and positrons, respectively) is their ability to annihilate one another. A similar behaviour is predicted for magnetic solitons(1)-localized spin textures that can be distinguished by their topological index Q. Theoretically, magnetic topological solitons with opposite values of Q, such as skyrmions(2) and their antiparticles (namely, antiskyrmions), are expected to be able to continuously merge and annihilate(3). However, experimental verification of such particle-antiparticle pair production and annihilation processes has been lacking. Here we report the creation and annihilation of skyrmion-antiskyrmion pairs in an exceptionally thin film of the cubic chiral magnet of B2O-type FeGe observed using transmission electron microscopy. Our observations are highly reproducible and are fully consistent with micromagnetic simulations. Our findings provide a new platform for the fundamental studies of particles and antiparticles based on magnetic solids and open new perspectives for practical applications of thin films of isotropic chiral magnets