Yu. Kucherenko

Strong ferromagnetism at the surface of an antiferromagnet caused by buried magnetic moments

Carrying a large, pure spin magnetic moment of 7 μB per atom in the half-filled 4f shell, divalent europium is an outstanding element for assembling novel magnetic devices in which a two-dimensional electron gas may be polarized due to exchange interaction with an underlying magnetically-active Eu layer. Here we show that the Si-Rh-Si surface trilayer of the antiferromagnet EuRh2Si2 bears a surface state, which exhibits an unexpected and large spin splitting controllable by temperature. The splitting sets in below ~32.5 K, well above the ordering temperature of the Eu 4f moments (~24.5 K) in the bulk, indicating a larger ordering temperature in the topmost Eu layers. The driving force for the itinerant ferromagnetism at the surface is the aforementioned exchange interaction. Such a splitting may also be induced into states of functional surface layers deposited onto the surface of EuRh2Si2 or similarly ordered magnetic materials with metallic or semiconducting properties.

The optical properties of

The optical properties of have been deduced using spectrophotometry and ellipsometry and calculated within the extended linear augmented plane wave framework in the energy range 0 - 6 eV. Good agreement amongst all approaches is obtained up to about 2 eV, beyond which there is some divergence between theory and experiment where, for reasons discussed, the theory needs further refinement.

ARPES view on surface and bulk hybridization phenomena in the antiferromagnetic Kondo lattice CeRh2Si2

The hybridization between localized 4f electrons and itinerant electrons in rare-earth-based materials gives rise to their exotic properties like valence fluctuations, Kondo behaviour, heavy-fermions, or unconventional superconductivity. Here we present an angle-resolved photoemission spectroscopy (ARPES) study of the Kondo lattice antiferromagnet CeRh2Si2, where the surface and bulk Ce-4f spectral responses were clearly resolved. The pronounced 4f 0 peak seen for the Ce terminated surface gets strongly suppressed in the bulk Ce-4f spectra taken from a Si-terminated crystal due to much larger f-d hybridization. Most interestingly, the bulk Ce-4f spectra reveal a fine structure near the Fermi edge reflecting the crystal electric field splitting of the bulk magnetic 4f 15/2 state. This structure presents a clear dispersion upon crossing valence states, providing direct evidence of f-d hybridization. Our findings give precise insight into f-d hybridization penomena and highlight their importance in the antiferromagnetic phases of Kondo lattices.

Wave-vector dependent intensity variations of the Kondo peak in photoemission from CePd3

Strong angle-dependent intensity variations of the Fermi-level feature are observed in 4d - 4f resonant photoemission spectra of CePd

The effect of transition probability on the shape of X-ray photoelectron spectra of diamond and silicon

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Angular distribution and spin polarization of Auger electrons following photoionization by polarized x-rays

(111), that reveal the periodicity of the lattice and largest intensity close to the Gamma points of the surface Brillouin zone. In the framework of a simplified periodic Anderson model the phenomena may quantitatively be described by a wave-vector dependence of the electron hopping matrix elements caused by Fermi-level crossings of non-4f-derived energy bands.

Local electronic structure around vacancies and vacancy-antisite complexes in beta-SiC

Abstract X-ray photoelectron spectra of valence bands in diamond and silicon have been calculated. It is shown that the probability of electron excitation from s-states is higher than that from p-states. The density of the electron states in the valence band of these crystals differs markedly from the energy distribution of photoelectrons.

The effect of the atomic relaxation around defects on the electronic structure and optical properties of β-SiC

Abstract Due to the absorption of circularly polarized light the spin of a core hole has a preferred value. The difference of the radial matrix elements for the two photoelectron channels and the energy dependence of the radial matrix elements has an important influence on the spin polarization. In the Auger transition process this spin polarization can be transferred to the Auger electron. The degree of the spin polarization of the Auger electrons mainly is determined by the core hole spin and by the contribution of the exchange integral in the auger matrix element. Furthermore it can be influenced by an exchange splitting of the core level due to an atomic magnetic moment and by a spin polarization of the density of states in the final state at the Auger electron energy. The transition probability and the spin polarization is calculated as well for the angle integrated as for the angle resolved Auger electron intensity for an atom of a bulk system to get the primary wave of a diffraction process of the Auger electron at the surrounding atoms. Results are presented for LMM Auger electrons of Ni. The influence of the exchange-splitting of the core levels involved in the Auger process is investigated for the LMM transition of Fe.

Transition probability effect on the shape of electron energy distribution in X-ray electron spectra of copper, silver and palladium

The local electronic structure around vacancies and vacancy-antisite complexes in cubic SiC has been calculated by means of the LMTO (linear muffin-tin orbital) method and the supercell approach. In order to improve the description of the electronic structure near the energy gap, the orbital-dependent LDA+U potential has been used. Different models for the displacement of the atoms around the defects are discussed. It has been shown that the atoms surrounding a silicon vacancy (VSi ) relax outwards from the vacancy, while for a carbon vacancy (VC ) a distortion of the tetrahedral arrangement of atoms is the more reliable model. The calculations of the local electronic structure performed for the vacancy-antisite complexes show that the VSi + SiC complex is characterized by a repulsive interaction between the SiC antisite and the three carbon atoms surrounding the vacancy. In contrast, the stability of the VC + CSi complex is determined by the bonding of the atoms surrounding the vacancy. In all cases the appearance of the localized electron state in the middle region of the energy gap is a characteristic feature of the vacancy-antisite complex. Some possible mechanisms of the annealing out of the vacancies in -SiC are discussed.

Theoretical investigation of the Auger spectra of Mg in different local atomic environments part 1. Magnesium and aluminium

The electronic structure and the optical properties associated with antisite defects in cubic SiC have been computed by means of the LMTO (linear muffin-tin orbital) method and the supercell approach. The orbital-dependent LDA + U potential (LDA≡local density approximation) used in the present work gives rise to an improved description both of the electronic structure near the energy gap and of the optical functions. Attention has been mainly focused on the effects caused by the local lattice relaxation around the defects. For compositions that deviate from the stoichiometric SiC towards higher content of carbon atoms, the small reduction of the energy gap which is observed experimentally can be explained only if the lattice relaxation is taken into account. The local electronic structure of antisite defects is characterized by s- and p-like resonance states in the valence band. Strong resonances occur also in the conduction band (especially for Csi). The Sic (Csi) antisite has more (fewer) valence electrons localized in the atomic sphere than the official Si (C) atom, but this difference is considerably reduced by the lattice relaxation. The results of the calculations show how the presence of point defects modifies the shape of the optical functions of the perfect SiC crystal and how the lattice relaxation has a strong effect on the fine structure of the optical functions. Different kinds of defect lead to different shapes of the optical functions.