67 research outputs found
Magnetic dichroism study on MnCoGa thin film using a combination of X-ray absorption and photoemission spectroscopy
Using circularly polarised radiation and a combination of bulk-sensitive hard
X-ray photoelectron spectroscopy and X-ray-absorption spectroscopy (XAS) we
studied the electronic and magnetic structure of epitaxial
MnCoGa thin films. Spin resolved Bloch spectral functions,
density of states as well as charge and magnetisation densities were
investigated by a first-principles analysis of full potential, fully
relativistic Korringa--Kohn--Rostoker calculations of the electronic structure.
The valence states were experimentally investigated by using linear dichroism
in the angular distribution and comparing the results to spin-resolved
densities of states. The linear dichroism in the valence band enabled a
symmetry analysis of the contributing states. The spectra were in good
agreement with the theoretical partial density of states. The element-specific,
spin-resolved, unoccupied densities of states for Co and Mn were analysed by
using XAS and X-ray magnetic circular dichroism (XMCD) at the edges.
The spectra were influenced by strong correlation effects. XMCD was used to
extract the site resolved magnetic moments. The experimental values of and agree very well with the
calculated magnetic moments. Magnetic circular dichroism in angle-resolved
photoelectron spectroscopy at the Mn and Co core level exhibited a
pronounced magnetic dichroism and confirmed the localised character of the Mn
valence states
Perpendicularly magnetized Mn-Co-Ga-based thin films with high coercive field
MnCoGa epitaxial thin films were grown on MgO substrates by
magnetron co-sputtering. Structures were tetragonal or cubic depending on Co
content. Composition dependence of saturation magnetization and uniaxial
magnetic anisotropy of the films were investigated. A high (1.2 MJ
m) was achieved for the MnCoGa film with the
magnetic moment 0.84. Valence band spectra were obtained by hard X-ray
photoelectron spectroscopy. Sharp peaks in the cubic case, which were absent in
the tetragonal case, prove that a van Hove singularity causes a band
Jahn-Teller effect with tetragonal distortion. Observations agree well with the
first-principles calculations
Electronic transport properties of electron- and hole-doped semiconducting C1b Heusler compounds: NiTi1−xMxSn (M=Sc, V)
The substitutional series of Heusler compounds NiTi1−xMxSn (where M=Sc,V and 0<x≤0.2) were synthesized and investigated with respect to their electronic structure and transport properties. The results show the possibility to create n-type and p-type thermoelectrics within one Heusler compound. The electronic structure and transport properties were calculated by all-electron ab initio methods and compared to the measurements. Hard x-ray photoelectron spectroscopy was carried out and the results are compared to the calculated electronic structure. Pure NiTiSn exhibits massive “in gap” states containing about 0.1 electrons per cell. The comparison of calculations, x-ray diffraction, and photoemission reveals that Ti atoms swapped into the vacant site are responsible for these states. The carrier concentration and temperature dependence of electrical conductivity, Seebeck coefficient, and thermal conductivity were investigated in the range from 10 to 300 K. The experimentally determined electronic structure and transport measurements agree well with the calculations. The sign of the Seebeck coefficient changes from negative for V to positive for Sc substitution. The high n-type and low p-type power factors are explained by differences in the chemical-disorder scattering-induced electric resistivity. Major differences appear because p-type doping (Sc) creates holes in the triply degenerate valence band at Γ whereas n-type doping (V) fills electrons in the single conduction band above the indirect gap at X what is typical for all semiconducting transition-metal-based Heusler compounds with C1b structure
A p-type Heusler compound: Growth, structure, and properties of epitaxial thin NiYBi films on MgO(100)
Epitaxial semiconducting NiYBi thin films were directly prepared on MgO(100)
substrates by magnetron sputtering. The intensity ratio of the (200) and (400)
diffraction peaks, I(200)/I(400) = 2.93, was close to the theoretical value
(3.03). The electronic structure of NiYBi was calculated using WIEN2k and a
narrow indirect band gap of width 210 meV was found. The valence band spectra
of the films obtained by linear dichroism in hard X-ray photoelectron
spectroscopy exhibit clear structures that are in good agreement with the
calculated band structure of NiYBi
Electronic structure and symmetry of valence states of epitaxial NiTiSn and NiZrHfSn thin films by hard x-ray photoelectron spectroscopy
The electronic band structure of thin films and superlattices made of Heusler
compounds with NiTiSn and NiZrHfSn composition was studied by
means of polarization dependent hard x-ray photoelectron spectroscopy. The
linear dichroism allowed to distinguish the symmetry of the valence states of
the different types of layered structures. The films exhibit a larger amount of
{\it "in-gap"} states compared to bulk samples. It is shown that the films and
superlattices grown with NiTiSn as starting layer exhibit an electronic
structure close to bulk materials
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