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Register a new userMagnetic dichroism in angular-resolved hard X-ray photoelectron spectroscopy from buried layers
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This work reports the measurement of magnetic dichroism in angular-resolved photoemission from in-plane magnetized buried thin films. The high bulk sensitivity of hard X-ray photoelectron spectroscopy (HAXPES) in combination with circularly polarized radiation enables the investigation of the magnetic properties of buried layers. HAXPES experiments with an excitation energy of 8 keV were performed on exchange-biased magnetic layers covered by thin oxide films. Two types of structures were investigated with the IrMn exchange-biasing layer either above or below the ferromagnetic layer: one with a CoFe layer on top and another with a Co$_2$FeAl layer buried beneath the IrMn layer. A pronounced magnetic dichroism is found in the Co and Fe $2p$ states of both materials. The localization of the magnetic moments at the Fe site conditioning the peculiar characteristics of the Co$_2$FeAl Heusler compound, predicted to be a half-metallic ferromagnet, is revealed from the magnetic dichroism detected in the Fe $2p$ states.
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We have investigated the electronic structure of the dilute magnetic semiconductor (DMS) $Ga_{0.98}Mn_{0.02}P$ and compared it to that of an undoped $GaP$ reference sample, using hard X-ray photoelectron spectroscopy (HXPS) and hard X-ray angle-resolved photoemission spectroscopy (HARPES) at energies of about 3 keV. We present experimental data, as well as theoretical calculations, in order to understand the role of the Mn dopant in the emergence of ferromagnetism in this material. Both core-level spectra and angle-resolved or angle-integrated valence spectra are discussed. In particular, the HARPES experimental data are compared to free-electron final-state model calculations and to more accurate one-step photoemission theory. The experimental results show differences between $Ga_{0.98}Mn_{0.02}P$ and $GaP$ in both angle-resolved and angle-integrated valence spectra. The $Ga_{0.98}Mn_{0.02}P$ bands are broadened due to the presence of Mn impurities that disturb the long-range translational order of the host $GaP$ crystal. Mn-induced changes of the electronic structure are observed over the entire valence band range, including the presence of a distinct impurity band close to the valence-band maximum of the DMS. These experimental results are in good agreement with the one-step photoemission calculations, and a prior HARPES study of $Ga_{0.97}Mn_{0.03}As$ and $GaAs$ (Gray et al. Nature Materials 11, 957 (2012)), demonstrating the strong similarity between these two materials. The Mn 2p and 3s core-level spectra also reveal an essentially identical state in doping both $GaAs$ and $GaP$.
We utilized X-ray photoemission electron microscopy (XPEEM) and X-ray photoelectron spectroscopy (XPS) to investigate the crystal surface of Weyl semimetal NbAs. XPEEM images present white and black contrast in both the Nb 3d and As 3d core level spectra. Surface-sensitive XPS spectra indicate that the entire surface of the sample contains both surface states of Nb 3d and As 3d, in form of oxides, and bulk states of NbAs. Estimated atomic percentage values nNb/nAs suggest that the surface is Nb-rich and asymmetric for white and black areas.
We propose a highly efficient atomically-resolved mode of electron magnetic chiral dichroism. This method exploits the recently introduced orbital angular momentum spectrometer to analyze the inelastically scattered electrons allowing for simultaneous dispersion in both energy and angular momentum. The technique offers several advantages over previous formulations of electron magnetic chiral dichroism as it requires much simpler experimental conditions in terms of specimen orientation and thickness. A novel simulation algorithm, based on the multislice description of the beam propagation, is used to anticipate the advantages of the new approach over current electron magnetic chiral dichroism implementations. Numerical calculations confirm an increased magnetic signal to noise ratio with in plane atomic resolution.
Magnetite (Fe3O4) thin films on GaAs have been studied with HArd X-ray PhotoElectron Spectroscopy (HAXPES) and low-energy electron diffraction. Films prepared under different growth conditions are compared with respect to stoichiometry, oxidation, and chemical nature. Employing the considerably enhanced probing depth of HAXPES as compared to conventional x-ray photoelectron spectroscopy (XPS) allows us to investigate the chemical state of the film-substrate interfaces. The degree of oxidation and intermixing at the interface are dependent on the applied growth conditions; in particular, we found that metallic Fe, As2O3, and Ga2O3 exist at the interface. These interface phases might be detrimental for spin injection from magnetite into GaAs.
We have carried out bulk-sensitive hard x-ray photoelectron spectroscopy (HAXPES) measurements on in-situ cleaved and ex-situ polished SmB6 single crystals. Using the multiplet-structure in the Sm 3d core level spectra, we determined reliably that the valence of Sm in bulk SmB6 is close to 2.55 at ~5 K. Temperature dependent measurements revealed that the Sm valence gradually increases to 2.64 at 300 K. From a detailed line shape analysis we can clearly observe that not only the J=0 but also the J=1 state of the Sm 4f 6 configuration becomes occupied at elevated temperatures. Making use of the polarization dependence, we were able to identify and extract the Sm 4f spectral weight of the bulk material. Finally, we revealed that the oxidized or chemically damaged surface region of the ex-situ polished SmB6 single crystal is surprisingly thin, about 1 nm only.
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