472 research outputs found
Proximity-induced ferromagnetism and chemical reactivity in few-layer VSe2 heterostructures
Among transition-metal dichalcogenides, mono and few-layers thick VSe2 has gained much recent attention following claims of intrinsic room-temperature ferromagnetism in this system, which have nonetheless proved controversial. Here, we address the magnetic and chemical properties of Fe/VSe2 heterostructure by combining element sensitive x-ray absorption spectroscopy and photoemission spectroscopy. Our x-ray magnetic circular dichroism results confirm recent findings that both native mono/few-layer and bulk VSe2 do not show intrinsic ferromagnetic ordering. Nonetheless, we find that ferromagnetism can be induced, even at room temperature, after coupling with a Fe thin film layer, with antiparallel alignment of the moment on the V with respect to Fe. We further consider the chemical reactivity at the Fe/VSe2 interface and its relation with interfacial magnetic coupling
Three-Dimensional Electronic Structure of type-II Weyl Semimetal WTe
By combining bulk sensitive soft-X-ray angular-resolved photoemission
spectroscopy and accurate first-principles calculations we explored the bulk
electronic properties of WTe, a candidate type-II Weyl semimetal featuring
a large non-saturating magnetoresistance. Despite the layered geometry
suggesting a two-dimensional electronic structure, we find a three-dimensional
electronic dispersion. We report an evident band dispersion in the reciprocal
direction perpendicular to the layers, implying that electrons can also travel
coherently when crossing from one layer to the other. The measured Fermi
surface is characterized by two well-separated electron and hole pockets at
either side of the point, differently from previous more surface
sensitive ARPES experiments that additionally found a significant quasiparticle
weight at the zone center. Moreover, we observe a significant sensitivity of
the bulk electronic structure of WTe around the Fermi level to electronic
correlations and renormalizations due to self-energy effects, previously
neglected in first-principles descriptions
Analysis of Metal-Insulator Crossover in Strained {SrRuO}3 Thin Films by X-ray Photoelectron Spectroscopy
The electronic properties of ultrathin epitaxial films of strontium ruthenate SrRuO3 perovskite oxide are modified by epitaxial strain, as determined by growing by pulsed laser deposition, on different the substrates. Electron transport measurements indicated that tensile strain deformation of the SrRuO3 unit cell reduces the metallicity of the material and reduces the metal-insulator-transition (MIT) temperatures. The shrinkage of the Ru-O-Ru buckling angle due to compressive strain is counterweighted by the increased overlap of the conduction Ru-4d orbitals with the O-2p ones due to the smaller interatomic distances resulting into an increased MIT temperature, i.e. a more conducting material. In the more metallic samples the core level x-ray photoemission spectroscopy lineshapes show the occurrence of an extra-peak at the lower binding energies of the main Ru-3d peaks that is attributed to screening, as observed in volume sensitive photoemission of the unstrained material
Electronic Structure of CeFeAsO1-xFx (x=0, 0.11/x=0.12) compounds
We report an extensive study on the intrinsic bulk electronic structure of
the high-temperature superconductor CeFeAsO0.89F0.11 and its parent compound
CeFeAsO by soft and hard x-ray photoemission, x-ray absorption and soft-x-ray
emission spectroscopies. The complementary surface/bulk probing depth, and the
elemental and chemical sensitivity of these techniques allows resolving the
intrinsic electronic structure of each element and correlating it with the
local structure, which has been probed by extended-x-ray absorption fine
structure spectroscopy. The measurements indicate a predominant 4f1 (i.e. Ce3+)
initial state configuration for Cerium and an effective valence-band-to-4f
charge-transfer screening of the core hole. The spectra also reveal the
presence of a small Ce f0 initial state configuration, which we assign to the
occurrence of an intermediate valence state. The data reveal a reasonably good
agreement with the partial density of states as obtained in standard density
functional calculations over a large energy range. Implications for the
electronic structure of these materials are discussed.Comment: Accepted for publication in Phys. Rev.
Interface bonding of a ferromagnetic/semiconductor junction : a photoemission study of Fe/ZnSe(001)
We have probed the interface of a ferromagnetic/semiconductor (FM/SC)
heterojunction by a combined high resolution photoemission spectroscopy and
x-ray photoelectron diffraction study. Fe/ZnSe(001) is considered as an example
of a very low reactivity interface system and it expected to constitute large
Tunnel Magnetoresistance devices. We focus on the interface atomic environment,
on the microscopic processes of the interface formation and on the iron
valence-band. We show that the Fe contact with ZnSe induces a chemical
conversion of the ZnSe outermost atomic layers. The main driving force that
induces this rearrangement is the requirement for a stable Fe-Se bonding at the
interface and a Se monolayer that floats at the Fe growth front. The released
Zn atoms are incorporated in substitution in the Fe lattice position. This
formation process is independent of the ZnSe surface termination (Zn or Se).
The Fe valence-band evolution indicates that the d-states at the Fermi level
show up even at submonolayer Fe coverage but that the Fe bulk character is only
recovered above 10 monolayers. Indeed, the Fe 1-band states,
theoretically predicted to dominate the tunneling conductance of Fe/ZnSe/Fe
junctions, are strongly modified at the FM/SC interface.Comment: 23 pages, 5 figures, submitted to Physical review
Electronic structure and spectroscopy of the quaternary Heusler alloy CoCrFeAl
Quaternary Heusler alloys CoCrFeAl with varying Cr to Fe
ratio were investigated experimentally and theoretically. The electronic
structure and spectroscopic properties were calculated using the full
relativistic Korringa-Kohn-Rostocker method with coherent potential
approximation to account for the random distribution of Cr and Fe atoms as well
as random disorder. Magnetic effects are included by the use of spin dependent
potentials in the local spin density approximation.
Magnetic circular dichroism in X-ray absorption was measured at the
edges of Co, Fe, and Cr of the pure compounds and the alloy in order to
determine element specific magnetic moments. Calculations and measurements show
an increase of the magnetic moments with increasing iron content. Resonant
(560eV - 800eV) soft X-ray as well as high resolution - high energy (keV) hard X-ray photo emission was used to probe the density of the
occupied states in CoCrFeAl.Comment: J.Phys.D_Appl.Phys. accepte
Magnetic anisotropy at the buried CoO/Fe interface
Interfaces between antiferromagnetic CoO and ferromagnetic Fe are typically characterized by the development of Fe oxides. Recently, it was shown that the use of a proper ultra-thin Co buffer layer prevents the formation of Fe oxides [Brambilla et al., Appl. Surf. Sci. 362, 374 (2016)]. In the present work, we investigate the magnetic properties of such an interface, and we find evidence for an in-plane uniaxial magnetic anisotropy, which is characterized by a multijump reversal behavior in the magnetization hysteresis loops. X-ray photoemission spectroscopy and element-sensitive hysteresis loops reveal that the occurrence of such an anisotropy is a phenomenon developing at the very interface
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