The growth of Fe nanoclusters oN the Ge（001） surface has been studied using low-temperature scanning tunneling microscopy （STM） and density functional theory （DFT） calculations. STM results indicate that Fe nucl...The growth of Fe nanoclusters oN the Ge（001） surface has been studied using low-temperature scanning tunneling microscopy （STM） and density functional theory （DFT） calculations. STM results indicate that Fe nucleates on the Ge（001） surface, forming well-ordered nanoclusters of uniform size. Depending on the preparation conditions, two types of nanoclusters were observed having either four or sixteen Fe atoms within a nanocluster. The results were confirmed by DFT calculations. Annealing the nanoclusters at 420 K leads to the formation of nanorow structures, due to cluster mobility at such temperature. The Fe nanoclusters and nanorow structures formed on the Ge（001） surface show a superparamagnetic behaviour as measured by X-ray magnetic circular dichroism.展开更多
X-ray magnetic circular dichroism （XMCD） has become an important and powerful tool because it allows the study of material properties in combination with elemental specificity, chemical state specificity, and magnet...X-ray magnetic circular dichroism （XMCD） has become an important and powerful tool because it allows the study of material properties in combination with elemental specificity, chemical state specificity, and magnetic specificity. A new soft X-ray magnetic circular dichroism apparatus has been developed at the Beijing Synchrotron Radiation Facility （BSRF）. The apparatus combines three experimental conditions： an ultra-high-vacuum environ- ment, moderate magnetic fields and in-situ sample preparation to measure the absorption signal. We designed a C-type dipole electromagnet that provides magnetic fields up to 0.5 T in parallel （or anti-parallel） direction rela- tive to the incoming X-ray beam. The performances of the electromagnet are measured and the results show good agreement with the simulation ones. Following film grown in situ by evaporation methods, XMCD measurements are performed. Combined polarization corrections, the magnetic moments of the Fe and Co films determined by sum rules are consistent with other theoretical predictions and experimental measurements.展开更多
Three ultra-short-period W/B4C multilayers （1.244 nm, 1.235 nm and 1.034 nm） have been fabricated and used for polarization measurement at the 4BTB Beamline at the Beijing Synchrotron Radiation Facility （BSRF）. By...Three ultra-short-period W/B4C multilayers （1.244 nm, 1.235 nm and 1.034 nm） have been fabricated and used for polarization measurement at the 4BTB Beamline at the Beijing Synchrotron Radiation Facility （BSRF）. By using the rotating analyzer ellipsometry method, the linear polarization degree of light emerging from this beamline has been measured and the circular polarization evaluated for 700-860 eV. The first soft X-ray magnetic circular dichroism measurements are carried out at BSRF by positioning the beamline aperture out of the plane of the electron storage ring.展开更多
X-ray magnetic circular dichroism in absorp- tion of the single-crystal iron layer deposited epitaxially on MgO substrate is studied. Spin and orbital moment, 0.069 and 2.33 μB, respectively, are calculated in terms ...X-ray magnetic circular dichroism in absorp- tion of the single-crystal iron layer deposited epitaxially on MgO substrate is studied. Spin and orbital moment, 0.069 and 2.33 μB, respectively, are calculated in terms of the XMCD sum rules. Our results are accordant to those pub- lished. Experiments show that the orbital moment would be decreased to that in bulk materials as iron film is thinned down, but spin moment changes little.展开更多
Electron magnetic circular dichroism opens a new door to explore magnetic properties by transmitted electrons in the transmission electron microscope. However, obtaining quantitative magnetic parameters, such as spin ...Electron magnetic circular dichroism opens a new door to explore magnetic properties by transmitted electrons in the transmission electron microscope. However, obtaining quantitative magnetic parameters, such as spin and orbital magnetic moment with element-specificity, goes a long way along with the development and improvement of this technique both in theoretical and experimental aspects. In this review, we will give a detailed description of the quantitative electron magnetic circular dichroism（EMCD） technique to measure magnetic parameters with spin-specificity, element-specificity,site-specificity, and orbital-spin-specificity. The discussion completely contains the procedures from raw experimental data acquisition to final magnetic parameters, together with the related custom code we have developed.展开更多
IN recent years,magnetic circular dichroism(MCD)demonstrated its unique advantages inanalysis of metal porphyrin and its interaction with protein.However,there were few re-ports about the application of MCD method in ...IN recent years,magnetic circular dichroism(MCD)demonstrated its unique advantages inanalysis of metal porphyrin and its interaction with protein.However,there were few re-ports about the application of MCD method in photosynthesis field.It is known that most pig-ments in PS Ⅱ-RC are metal porphyrin type.This note reports the MCD spectrum of PS Ⅱ-展开更多
In this work, the magnetocrystalline anisotropy energy(MAE) on the surface of FeCoalloy film is extracted from x-ray magnetic linear dichroism(XMLD) experiments. The result indicates that the surface MAE value is nega...In this work, the magnetocrystalline anisotropy energy(MAE) on the surface of FeCoalloy film is extracted from x-ray magnetic linear dichroism(XMLD) experiments. The result indicates that the surface MAE value is negatively correlated with thickness. Through spectrum calculations and analysis, we find that besides the thickness effect, another principal possible cause may be the shape anisotropy resulting from the presence of interface roughness. These two factors lead to different electron structures on the fermi surface with different exchange fields, which produces different spin–orbit interaction anisotropies.展开更多
Spin chiral anisotropy(SChA)refers to the occurrence of different spin polarization in antipodal chiral structures.Herein,we report the SChA in diamagnetic chiral mesostructured In2O3 films(CMIFs)with manifestation of...Spin chiral anisotropy(SChA)refers to the occurrence of different spin polarization in antipodal chiral structures.Herein,we report the SChA in diamagnetic chiral mesostructured In2O3 films(CMIFs)with manifestation of chirality-dependent magnetic circular dichroism(MCD)signals.CMIFs were grown on fluorine-doped tin dioxide conductive glass(FTO)substrates,which were synthesized via a hydrothermal route,with malic acid used as the symmetry-breaking agent.Two levels of chirality have been identified in CMIFs:primary nanoflakes with atomically twisted crystal lattices and secondary helical stacking of the nanoflakes.CMIFs exhibit chirality-dependent asymmetric MCD signals due to the different interactions of chirality-induced effective magnetic field and external magnetic field,which distinguish from the commonly observed external magnetic fielddependent symmetric MCD signals.These findings provide insights into spin manipulation of spin-paired diamagnets.展开更多
Chirality is omnipresent among biological materials,such as amino acids,sugars,and DNA[1].It plays a vital role in wide-ranging applications including biomedicine,nonlinear optics,and negative index metamaterials[2-4]...Chirality is omnipresent among biological materials,such as amino acids,sugars,and DNA[1].It plays a vital role in wide-ranging applications including biomedicine,nonlinear optics,and negative index metamaterials[2-4].The chiral structures of molecules and supramolecular systems may cause differential absorption of left-and right-handed circularly polarized light leading to circular dichroism(CD)activity.展开更多
Modern design of superior multi-functional alloys composed of several principal components requires in-depth studies of their local structure for developing desired macroscopic properties.Herein,peculiarities of atomi...Modern design of superior multi-functional alloys composed of several principal components requires in-depth studies of their local structure for developing desired macroscopic properties.Herein,peculiarities of atomic arrangements on the local scale and electronic states of constituent elements in the single-phase face-centered cubic(fcc)-and body-centered cubic(bcc)-structured high-entropy Alx-CrFeCoNi alloys(x=0.3 and 3,respectively)are explored by element-specific X-ray absorption spectroscopy in hard and soft X-ray energy ranges.Simulations based on the reverse Monte Carlo approach allow to perform a simultaneous fit of extended X-ray absorption fine structure spectra recorded at K absorption edges of each 3d constituent and to reconstruct the local environment within the first coordination shells of absorbers with high precision.The revealed unimodal and bimodal distributions of all five elements are in agreement with structure-dependent magnetic properties of studied alloys probed by magnetometry.A degree of surface atoms oxidation uncovered by soft X-rays suggests different kinetics of oxide formation for each type of constituents and has to be taken into account.X-ray magnetic circular dichroism technique employed at L2,3 absorption edges of transition metals demonstrates reduced magnetic moments of 3d metal constituents in the sub-surface region of in situ cleaned fcc-structured Al0.3-CrFeCoNi compared to their bulk values.Extended to nanostructured versions of multicomponent alloys,such studies would bring new insights related to effects of high entropy mixing on low dimensions.展开更多
The huge atomic heterogeneity of high-entropy materials along with a possibility to unravel the behavior of individual components at the atomic scale suggests a great promise in designing new compositionally complex s...The huge atomic heterogeneity of high-entropy materials along with a possibility to unravel the behavior of individual components at the atomic scale suggests a great promise in designing new compositionally complex systems with the desired multifunctionality.Herein,we apply multi-edge X-ray absorption spectroscopy(extended X-ray absorption fine structure(EXAFS),Xray absorption near edge structure(XANES),and X-ray magnetic circular dichroism(XMCD))to probe the structural,electronic,and magnetic properties of all individual constituents in the single-phase face-centered cubic(fcc)-structured nanocrystalline thin film of Cr_(20)Mn_(26)Fe_(18)Co_(19)Ni_(17)(at.%)high-entropy alloy on the local scale.The local crystallographic ordering and componentdependent lattice displacements were explored within the reverse Monte Carlo approach applied to EXAFS spectra collected at the K absorption edges of several constituents at room temperature.A homogeneous short-range fcc atomic environment around the absorbers of each type with very similar statistically averaged interatomic distances(2.54-2.55Å)to their nearest-neighbors and enlarged structural relaxations of Cr atoms were revealed.XANES and XMCD spectra collected at the L2,3 absorption edges of all principal components at low temperature from the oxidized and in situ cleaned surfaces were used to probe the oxidation states,the changes in the electronic structure,and magnetic behavior of all constituents at the surface and in the sub-surface volume of the film.The spin and orbital magnetic moments of Fe,Co,and Ni components were quantitatively evaluated.The presence of magnetic phase transitions and the co-existence of different magnetic phases were uncovered by conventional magnetometry in a broad temperature range.展开更多
Recent discoveries of intrinsic two-dimensional(2D)magnets open up vast opportunities to address fundamental problems in condensed matter physics,giving rise to applications from ultra-compact spintronics to quantum c...Recent discoveries of intrinsic two-dimensional(2D)magnets open up vast opportunities to address fundamental problems in condensed matter physics,giving rise to applications from ultra-compact spintronics to quantum computing.The ever-growing material landscape of 2D magnets lacks,however,carbon-based systems,prominent in other areas of 2D research.Magnetization measurements of the Eu/graphene compound-a monolayer of the EuC_(6) stoichiometry-reveal the emergence of 2D ferromagnetism but detailed studies of competing magnetic states are still missing.Here,we employ element-selective X-ray absorption spectroscopy(XAS)and magnetic circular dichroism(XMCD)to establish the magnetic structure of monolayer EuC6.The system exhibits the anomalous Hall effect,negative magnetoresistance,and magnetization consistent with a ferromagnetic state but the saturation magnetic moment(about 2.5/%/Eu)is way too low for the half-filled f-shells of Eu^(2+)ions.Combined XAS/XMCD studies at the Eu L3 absorption edge probe the EuC6 magnetism in high fields and reveal the nature of the missing magnetic moments.The results are set against XMCD studies in Eu/silicene and Eu/germanene to establish monolayer EuC6 as a prominent member of the family of Eu-based 2D magnets combining the celebrated graphene properties with a strong magnetism of europium.展开更多
基金This work was supported by Science Foundation Ireland （Principal Investigator grant No. 06/IN.1/191 and Research Frontiers Programme grant No. 07/ RFP/MASF185）. The authors wish to thank Trinity College High Performance Cluster, funded by the Higher Education Authority under the Program for Research in Third Level Institutes, for the use of their computing facilities.
文摘The growth of Fe nanoclusters oN the Ge（001） surface has been studied using low-temperature scanning tunneling microscopy （STM） and density functional theory （DFT） calculations. STM results indicate that Fe nucleates on the Ge（001） surface, forming well-ordered nanoclusters of uniform size. Depending on the preparation conditions, two types of nanoclusters were observed having either four or sixteen Fe atoms within a nanocluster. The results were confirmed by DFT calculations. Annealing the nanoclusters at 420 K leads to the formation of nanorow structures, due to cluster mobility at such temperature. The Fe nanoclusters and nanorow structures formed on the Ge（001） surface show a superparamagnetic behaviour as measured by X-ray magnetic circular dichroism.
基金Supported by National Natural Science Foundation of China(61204008)
文摘X-ray magnetic circular dichroism （XMCD） has become an important and powerful tool because it allows the study of material properties in combination with elemental specificity, chemical state specificity, and magnetic specificity. A new soft X-ray magnetic circular dichroism apparatus has been developed at the Beijing Synchrotron Radiation Facility （BSRF）. The apparatus combines three experimental conditions： an ultra-high-vacuum environ- ment, moderate magnetic fields and in-situ sample preparation to measure the absorption signal. We designed a C-type dipole electromagnet that provides magnetic fields up to 0.5 T in parallel （or anti-parallel） direction rela- tive to the incoming X-ray beam. The performances of the electromagnet are measured and the results show good agreement with the simulation ones. Following film grown in situ by evaporation methods, XMCD measurements are performed. Combined polarization corrections, the magnetic moments of the Fe and Co films determined by sum rules are consistent with other theoretical predictions and experimental measurements.
基金Supported by National Natural Science Foundation of China(11075176, 10435050)
文摘Three ultra-short-period W/B4C multilayers （1.244 nm, 1.235 nm and 1.034 nm） have been fabricated and used for polarization measurement at the 4BTB Beamline at the Beijing Synchrotron Radiation Facility （BSRF）. By using the rotating analyzer ellipsometry method, the linear polarization degree of light emerging from this beamline has been measured and the circular polarization evaluated for 700-860 eV. The first soft X-ray magnetic circular dichroism measurements are carried out at BSRF by positioning the beamline aperture out of the plane of the electron storage ring.
文摘X-ray magnetic circular dichroism in absorp- tion of the single-crystal iron layer deposited epitaxially on MgO substrate is studied. Spin and orbital moment, 0.069 and 2.33 μB, respectively, are calculated in terms of the XMCD sum rules. Our results are accordant to those pub- lished. Experiments show that the orbital moment would be decreased to that in bulk materials as iron film is thinned down, but spin moment changes little.
文摘Electron magnetic circular dichroism opens a new door to explore magnetic properties by transmitted electrons in the transmission electron microscope. However, obtaining quantitative magnetic parameters, such as spin and orbital magnetic moment with element-specificity, goes a long way along with the development and improvement of this technique both in theoretical and experimental aspects. In this review, we will give a detailed description of the quantitative electron magnetic circular dichroism（EMCD） technique to measure magnetic parameters with spin-specificity, element-specificity,site-specificity, and orbital-spin-specificity. The discussion completely contains the procedures from raw experimental data acquisition to final magnetic parameters, together with the related custom code we have developed.
文摘IN recent years,magnetic circular dichroism(MCD)demonstrated its unique advantages inanalysis of metal porphyrin and its interaction with protein.However,there were few re-ports about the application of MCD method in photosynthesis field.It is known that most pig-ments in PS Ⅱ-RC are metal porphyrin type.This note reports the MCD spectrum of PS Ⅱ-
基金supported by the National Natural Science Foundation of China(Grant Nos.11075176 and 11375131)
文摘In this work, the magnetocrystalline anisotropy energy(MAE) on the surface of FeCoalloy film is extracted from x-ray magnetic linear dichroism(XMLD) experiments. The result indicates that the surface MAE value is negatively correlated with thickness. Through spectrum calculations and analysis, we find that besides the thickness effect, another principal possible cause may be the shape anisotropy resulting from the presence of interface roughness. These two factors lead to different electron structures on the fermi surface with different exchange fields, which produces different spin–orbit interaction anisotropies.
基金supported by the National Key Research and Development Program of China(No.2021YFA1200301,S.A.C.)the National Natural Science Foundation of China(Nos.21931008,S.A.C.and 21975184,Y.Y.D.)Shanghai Pilot Program for Basic Research-Shanghai Jiao Tong University(No.21TQ1400219).
文摘Spin chiral anisotropy(SChA)refers to the occurrence of different spin polarization in antipodal chiral structures.Herein,we report the SChA in diamagnetic chiral mesostructured In2O3 films(CMIFs)with manifestation of chirality-dependent magnetic circular dichroism(MCD)signals.CMIFs were grown on fluorine-doped tin dioxide conductive glass(FTO)substrates,which were synthesized via a hydrothermal route,with malic acid used as the symmetry-breaking agent.Two levels of chirality have been identified in CMIFs:primary nanoflakes with atomically twisted crystal lattices and secondary helical stacking of the nanoflakes.CMIFs exhibit chirality-dependent asymmetric MCD signals due to the different interactions of chirality-induced effective magnetic field and external magnetic field,which distinguish from the commonly observed external magnetic fielddependent symmetric MCD signals.These findings provide insights into spin manipulation of spin-paired diamagnets.
基金This work was supported by the National Natural Science Foundation of China(Nos.21975095,21671079 and 21373100)the“111”Project of China(No.B17020)the Fund of the State Key Laboratory of Inorganic Synthesis and Preparative Chemistry(Jilin University),China(No.1G3211454461).
文摘Chirality is omnipresent among biological materials,such as amino acids,sugars,and DNA[1].It plays a vital role in wide-ranging applications including biomedicine,nonlinear optics,and negative index metamaterials[2-4].The chiral structures of molecules and supramolecular systems may cause differential absorption of left-and right-handed circularly polarized light leading to circular dichroism(CD)activity.
基金The authors thank the Helmholtz-Zentrum Berlin for the provision of access to synchrotron radiation facilities and allocation of synchrotron radiation at the PM2-VEKMAG,BAMline,and UE46_PGM-1 beamlines of BESSY II at HZB as well as measurement time for magnetometry at HZB CoreLab for Quantum Materials.A.S.acknowledges personal funding from CALIPSOplus project(the Grant Agreement no.730872 from the EU Framework Programme for Research and Innovation HORIZON 2020)The financial support for the VEKMAG project and the PM2-VEKMAG beamline by the German Federal Ministry for Education and Research(Nos.BMBF 05K10PC2,05K10WR1,05K10KE1)by HZB is cordially acknowledged by all co-authors.Steffen Rudorff is acknowledged for technical support.Institute of Solid State Physics,University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No.739508,project CAMART2.
文摘Modern design of superior multi-functional alloys composed of several principal components requires in-depth studies of their local structure for developing desired macroscopic properties.Herein,peculiarities of atomic arrangements on the local scale and electronic states of constituent elements in the single-phase face-centered cubic(fcc)-and body-centered cubic(bcc)-structured high-entropy Alx-CrFeCoNi alloys(x=0.3 and 3,respectively)are explored by element-specific X-ray absorption spectroscopy in hard and soft X-ray energy ranges.Simulations based on the reverse Monte Carlo approach allow to perform a simultaneous fit of extended X-ray absorption fine structure spectra recorded at K absorption edges of each 3d constituent and to reconstruct the local environment within the first coordination shells of absorbers with high precision.The revealed unimodal and bimodal distributions of all five elements are in agreement with structure-dependent magnetic properties of studied alloys probed by magnetometry.A degree of surface atoms oxidation uncovered by soft X-rays suggests different kinetics of oxide formation for each type of constituents and has to be taken into account.X-ray magnetic circular dichroism technique employed at L2,3 absorption edges of transition metals demonstrates reduced magnetic moments of 3d metal constituents in the sub-surface region of in situ cleaned fcc-structured Al0.3-CrFeCoNi compared to their bulk values.Extended to nanostructured versions of multicomponent alloys,such studies would bring new insights related to effects of high entropy mixing on low dimensions.
文摘The huge atomic heterogeneity of high-entropy materials along with a possibility to unravel the behavior of individual components at the atomic scale suggests a great promise in designing new compositionally complex systems with the desired multifunctionality.Herein,we apply multi-edge X-ray absorption spectroscopy(extended X-ray absorption fine structure(EXAFS),Xray absorption near edge structure(XANES),and X-ray magnetic circular dichroism(XMCD))to probe the structural,electronic,and magnetic properties of all individual constituents in the single-phase face-centered cubic(fcc)-structured nanocrystalline thin film of Cr_(20)Mn_(26)Fe_(18)Co_(19)Ni_(17)(at.%)high-entropy alloy on the local scale.The local crystallographic ordering and componentdependent lattice displacements were explored within the reverse Monte Carlo approach applied to EXAFS spectra collected at the K absorption edges of several constituents at room temperature.A homogeneous short-range fcc atomic environment around the absorbers of each type with very similar statistically averaged interatomic distances(2.54-2.55Å)to their nearest-neighbors and enlarged structural relaxations of Cr atoms were revealed.XANES and XMCD spectra collected at the L2,3 absorption edges of all principal components at low temperature from the oxidized and in situ cleaned surfaces were used to probe the oxidation states,the changes in the electronic structure,and magnetic behavior of all constituents at the surface and in the sub-surface volume of the film.The spin and orbital magnetic moments of Fe,Co,and Ni components were quantitatively evaluated.The presence of magnetic phase transitions and the co-existence of different magnetic phases were uncovered by conventional magnetometry in a broad temperature range.
基金supported by NRC“Kurchatov Institute”(No.1055(characterization))the Russian Foundation for Basic Research(grant 19-07-00249(transport measurements)),and the Russian Science Foundation(grants 19-19-00009(synthesis)and 20-79-10028(magnetization measurements)).D.V.A.acknowledges support from the Presidents scholarship(SP 1398.2019.5).
文摘Recent discoveries of intrinsic two-dimensional(2D)magnets open up vast opportunities to address fundamental problems in condensed matter physics,giving rise to applications from ultra-compact spintronics to quantum computing.The ever-growing material landscape of 2D magnets lacks,however,carbon-based systems,prominent in other areas of 2D research.Magnetization measurements of the Eu/graphene compound-a monolayer of the EuC_(6) stoichiometry-reveal the emergence of 2D ferromagnetism but detailed studies of competing magnetic states are still missing.Here,we employ element-selective X-ray absorption spectroscopy(XAS)and magnetic circular dichroism(XMCD)to establish the magnetic structure of monolayer EuC6.The system exhibits the anomalous Hall effect,negative magnetoresistance,and magnetization consistent with a ferromagnetic state but the saturation magnetic moment(about 2.5/%/Eu)is way too low for the half-filled f-shells of Eu^(2+)ions.Combined XAS/XMCD studies at the Eu L3 absorption edge probe the EuC6 magnetism in high fields and reveal the nature of the missing magnetic moments.The results are set against XMCD studies in Eu/silicene and Eu/germanene to establish monolayer EuC6 as a prominent member of the family of Eu-based 2D magnets combining the celebrated graphene properties with a strong magnetism of europium.
