550 research outputs found
Biaxial Strain in the Hexagonal Plane of MnAs Thin Films: The Key to Stabilize Ferromagnetism to Higher Temperature
The alpha-beta magneto-structural phase transition in MnAs/GaAs(111)
epilayers is investigated by elastic neutron scattering. The in-plane parameter
of MnAs remains almost constant with temperature from 100 K to 420 K, following
the thermal evolution of the GaAs substrate. This induces a temperature
dependent biaxial strain that is responsible for an alpha-beta phase
coexistence and, more important, for the stabilization of the ferromagnetic
alpha-phase at higher temperature than in bulk. We explain the premature
appearance of the beta-phase at 275 K and the persistence of the ferromagnetic
alpha-phase up to 350 K with thermodynamical arguments based on the MnAs phase
diagram. It results that the biaxial strain in the hexagonal plane is the key
parameter to extend the ferromagnetic phase well over room temperature.Comment: 4 pages, 3 figures, accepted for publication in Physical Review
Letter
Biaxial Strain in the Hexagonal Plane of MnAs Thin Films: The Key to Stabilize Ferromagnetism to Higher Temperature
The alpha-beta magneto-structural phase transition in MnAs/GaAs(111)
epilayers is investigated by elastic neutron scattering. The in-plane parameter
of MnAs remains almost constant with temperature from 100 K to 420 K, following
the thermal evolution of the GaAs substrate. This induces a temperature
dependent biaxial strain that is responsible for an alpha-beta phase
coexistence and, more important, for the stabilization of the ferromagnetic
alpha-phase at higher temperature than in bulk. We explain the premature
appearance of the beta-phase at 275 K and the persistence of the ferromagnetic
alpha-phase up to 350 K with thermodynamical arguments based on the MnAs phase
diagram. It results that the biaxial strain in the hexagonal plane is the key
parameter to extend the ferromagnetic phase well over room temperature.Comment: 4 pages, 3 figures, accepted for publication in Physical Review
Letter
Local magnetic moment coupling of Gd on Fe(100) studied by magnetic dichroism in angular-dependent photoemission
We measured the magnetic linear dichroism in the angular distribution (MLDAD) of photoemission of thin Gd layers on Fe(100). At low photon energies large MLDAD asymmetries, up to 40%, in the (Formula presented) photoemission were observed. The line shape and the photon-energy dependence of the measured MLDAD are in good agreement with theoretical results. Analysis of the (Formula presented) and (Formula presented) magnetic signals indicates an antiferromagnetic coupling between Gd and Fe, confirming previous findings. We also demonstrate that the MLDAD plus-minus feature is governed by the orbital magnetic moment of the core hole state
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
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
Prominent 5d-orbital contribution to the conduction electrons in gold
We have examined the valence-band electronic structures of gold and silver in
the same column in the periodic table with nominally filled d orbitals by means
of a recently developed polarization-dependent hard x-ray photoemission.
Contrary to a common expectation, it is found that the 5d-orbital electrons
contribute prominently to the conduction electrons in gold while the conduction
electrons in silver are to some extent free-electron-like with negligible 4d
contribution, which could be related to a well-known fact that gold is more
stable than silver in air. The 4d electron correlation effects are found to be
essential for the conduction electron character in silver.Comment: 8 pages, 4 figures, to be appeared in New J. Phys
Depth dependence of itinerant character in Mn-substituted Sr3Ru2O7
We present a core-level photoemission study of Sr3(Ru 1-xMnx)2O7, in which we
monitor the evolution of the Ru-3d fine structure versus Mn substitution and
probing depth. In both Ru 3d3/2 and 3d5/2 core levels we observe a clear
suppression of the metallic features, i.e. the screened peaks, implying a sharp
transition from itinerant to localized character already at low Mn
concentrations. The comparison between soft and hard x-ray photoemission, which
provides tunable depth sensitivity, reveals that the degree of
localized/metallic character for Ru is different at the surface than in the
bulk.Comment: 10 pages, 4 figures, 1 tabl
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.
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
High energy, high resolution photoelectron spectroscopy of Co2Mn(1-x)Fe(x)Si
This work reports on high resolution photoelectron spectroscopy for the
valence band of Co2Mn(1-x)Fe(x)Si (x=0,0.5,1) excited by photons of about 8 keV
energy. The measurements show a good agreement to calculations of the
electronic structure using the LDA+U scheme. It is shown that the high energy
spectra reveal the bulk electronic structure better compared to low energy XPS
spectra. The high resolution measurements of the valence band close to the
Fermi energy indicate the existence of the gap in the minority states for all
three alloys.Comment: 14 pages, 5 figures, submitted to J. Phys. D: Appl. Phy
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