A small fluctuation of the photon beam position will affect the intensity and polarization characteristics of synchrotron radiation （SR） when it enters an endstation through the related beamline. In this paper, by c...A small fluctuation of the photon beam position will affect the intensity and polarization characteristics of synchrotron radiation （SR） when it enters an endstation through the related beamline. In this paper, by changing the electron orbit equilibrium position in the vertical direction, we have measured the corresponding changes in the absorption strength of the SR with a gold mesh in different chopper aperture positions. It is found that for three aperture positions, the absorption intensity of the gold mesh shows a good Gaussian distribution as the photon beam position moves, while the ratio of the SR intensity passing through the upper and lower apertures shows a monotonous variation. This suggests a new method for estimating the circular polarization degree of SR originating from the bending magnet based on our current measurement.展开更多
The BL07U beamline is a new extreme ultraviolet and soft X-ray beamline housed in the Shanghai Synchrotron Radiation Facility. Beamlines are used in nano-resolved angle-resolved photoemission spectroscopy(nano-ARPES),...The BL07U beamline is a new extreme ultraviolet and soft X-ray beamline housed in the Shanghai Synchrotron Radiation Facility. Beamlines are used in nano-resolved angle-resolved photoemission spectroscopy(nano-ARPES), spin-resolved angle-resolved photoemission spectroscopy(spin-ARPES), X-ray magnetic circular dichroism spectroscopy, and X-ray magnetic linear dichroism spectroscopy for certain scientific research. The BL07U beamline, which is based on a pair of elliptical polarized undulators and a variable-included-angle plane-grating monochromator, delivers circularly or linear polarized X-rays within the energy range of 50–2000 eV. The beamline features two branches: One dedicated to nano-ARPES,which has a minimum spot size of only ~ 200 nm, and another branch comprising spin-ARPES, a vector magnetic field, and superconductive magnetic end-station.展开更多
A heterometallic Ni_(4)Tb field-induced SMM has been grafted onto the surface of superparamagnetic iron oxide nanoparticles.The magnetic coupling within the Ni_(4)Tb and between the Ni_(4)Tb and iron oxide nanoparticl...A heterometallic Ni_(4)Tb field-induced SMM has been grafted onto the surface of superparamagnetic iron oxide nanoparticles.The magnetic coupling within the Ni_(4)Tb and between the Ni_(4)Tb and iron oxide nanoparticle has been studied by element specific XMCD measurements.The coupling between Ni and Tb is ferromagnetic and the complex remains intact when grafted onto the iron oxide nanoparticles.展开更多
The measurement of the magnetic anisotropy of[Fe{(3,5-(CH_(3))_(2)Pz)_(3)BH}_(2)],where Pz=pyrazole,in its high spin state(S=2)by X-ray Magnetic Circular Dichroism(XMCD)spectroscopy when assembled as an organized mono...The measurement of the magnetic anisotropy of[Fe{(3,5-(CH_(3))_(2)Pz)_(3)BH}_(2)],where Pz=pyrazole,in its high spin state(S=2)by X-ray Magnetic Circular Dichroism(XMCD)spectroscopy when assembled as an organized monolayer on Cu(111)shows the presence of a hard axis of magnetization(positive axial zero-field splitting-ZFS-parameter D).Combining magnetization and multifrequency electron paramagnetic resonance spectroscopy on a reference compound,[Fe{(3-(Ph)Pz)_(3)BH}_(2)],of the same family and ab initio wave function based theoretical calculations,we demonstrate that the magnetic anisotropy of the assembled molecules is not affected when they are present at the substrate/vacuum interface.Comparing our results with those of a reported complex having an almost identical FeN_(6)coordination sphere but an easy axis of magnetization(corresponding to a negative D value),we show that the nature of the magnetic anisotropy(easy/hard axis)is governed by the torsion angle(Ψ)defined by the relative orientation of the pyrazole five-membered rings to the pseudo three-fold axis of the molecules.The rigidity of the(Pz)_(3)BH tridentate ligands,where the three pyrazole moieties are held by the BH group,allows only very slight changes in the torsion angle even when the molecules are in a dissymmetric environment such as an interface.This is the origin of the robust magnetic anisotropy of this family of compounds.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
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
Co-Fe alloy films have such properties as high saturation magnetization, high Curie tem- perature and low coercive force. It is of importance to study the origin of high saturation magnetization in these alloys. In th...Co-Fe alloy films have such properties as high saturation magnetization, high Curie tem- perature and low coercive force. It is of importance to study the origin of high saturation magnetization in these alloys. In this paper, we study the spin (ms) and orbital moments (mo) of Fe and Co in the Co0.9Fe0.1 film by using X-ray magnetic circular dichroism (XMCD) and SQUID magnetometry. The ms and mo for Co are 1.58 and 0.31 μB, and for Fe are 1.63 and 0.36 μB respectively. The average magnetic moment (1.90 μB) determined by XMCD is in agreement with that obtained from SQUID measurements. The total magnetic moment ratio of Fe to Co is 10.5:89.5, while the ratio of the spin to orbital moment is 83.4:16.6. Considering the separation of the spin and orbital moment, an outcome of mFe-spin : mFe-orbit : mCo-spin : mCo-orbit = 8.6:1.9:74.8:14.7 is obtained.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
Two-dimension(2D)magnets have recently developed into a class of stoichiometric materials with prospective applications in ultra-compact spintronics and quantum computing.Their functionality is particularly rich when ...Two-dimension(2D)magnets have recently developed into a class of stoichiometric materials with prospective applications in ultra-compact spintronics and quantum computing.Their functionality is particularly rich when different magnetic orders are competing in the same material.Metalloxenes REX2(RE=Eu,Gd;X=Si,Ge),silicene or germanene—heavy counterparts of graphene—coupled with a layer of rare-earth metals,evolve from three-dimension(3D)antiferromagnets in multilayer structures to 2D ferromagnets in a few monolayers.This evolution,however,does not lead to fully saturated 2D ferromagnetism,pointing at a possibility of coexisting/competing magnetic states.Here,REX2 magnetism is explored with element-selective X-ray magnetic circular dichroism(XMCD).The measurements are carried out for GdSi2,EuSi2,GdGe2,and EuGe2 of different thicknesses down to 1 monolayer employing K absorption edges of Si and Ge as well as M and L edges of the rare-earths.They access the magnetic state in REX2 and determine the seat of magnetism,orbital,and spin contributions to the magnetic moment.High-field measurements probe remnants of the bulk antiferromagnetism in 2D REX2.The results provide a new platform for studies of complex magnetic structures in 2D materials.展开更多
In recent decades, magnetoelectric effect in multiferroic materials has attracted extensive attention owing to the upcoming demands for new-generation multi-functional magnetoelectronic devices, such as transducer, se...In recent decades, magnetoelectric effect in multiferroic materials has attracted extensive attention owing to the upcoming demands for new-generation multi-functional magnetoelectronic devices, such as transducer, sensor and so on. This gives people a strong push to explore the multiferroic materials with a reduced dimension and effective coupling between electric and magnetic orderings, especially at room temperature. Due to the weak magnetoelectric coupling strength in sing-phase multiferroic materials, scientists start to design nanocomposites and artificial nanostructures with strong coupling among order parameters(lattice, charge, spin and orbital). In this review, we will introduce recent major progresses of magnetoelectric coupling in multiferroic nanocomposites across their interfaces from the following four aspects: strain effect, charge transfer, magnetic exchange interaction and orbital hybridization, based on their coupling mechanisms. Through a full understanding of the above coupling among these orderings, it is possible to achieve the nanoscale modulation of magnetization(ferroelectric polarization) by external electric(magnetic) field. Apart from the magnetoelectric coupling, those artificially functional nanocomposites provide us a platform to explore and study the emerging physical phenomena so that we can design self-assembled nanostructures to tailor novel functionalities in future applications.展开更多
Patterned ferromagnetic thin film shows promising applications in ultra-high density magnetic storage,magnetoresistive transducer,magnetic random access memory and many other devices.Since the performance of these dev...Patterned ferromagnetic thin film shows promising applications in ultra-high density magnetic storage,magnetoresistive transducer,magnetic random access memory and many other devices.Since the performance of these devices is closely associated with the magnetic properties of the etched patterns,it is necessary to study the effects of freshly etched surface oxidation on the magnetic properties of the patterned microstructures.In the current work,were carried out an X-ray Magnetic Circular Dichroism(XMCD) study on a 50 nm Co 0.9 Fe 0.1 continuous thin film and a related patterned Co 0.9 Fe 0.1 grating structure etched with a 2 μm period.Based on the sum rules,the spin and orbital moments were calculated for these two samples,respectively.The results indicated that the spin and orbital moments of grating structure(1.34μ B and 0.24μ B,respectively) decreased 17.3% compared with the corresponding continuous film(1.62μ B and 0.29μ B,respectively).We proposed that the moment decreasing of the patterned grating structure was mainly caused by the etched surface oxidation during the pattern manufacture process.The oxidation ratio of Co element in the patterned grating structure is 14.4% calculated from X-ray absorption spectroscopy(XAS) measurement.Considering the oxidation ratio,we amend the spin and orbital moment of Co and the amended result is basically in accordance with that of continuous film,demonstrating that the difference of the spin and orbital moments between the sub-micron grating unit and the continuous film is really caused by the oxidation.展开更多
Magnetite Fe304 （ferrite） has attracted considerable interest for its exceptional physical properties： It is predicted to be a semimetallic ferromagnetic with a high Curie temperature, it displays a metal-insulator...Magnetite Fe304 （ferrite） has attracted considerable interest for its exceptional physical properties： It is predicted to be a semimetallic ferromagnetic with a high Curie temperature, it displays a metal-insulator transition, and has potential oxide-electronics applications. Here, we fabricate a high-magnetization （〉 1 Tesla） high-resistance （-0.1 Ωcm） sub-nanostructured （grain size 〈 3 nm） Fe304 film via grain-size control and nano-engineering. We report a new phenomenon of spin- flipping of the valence-spin tetrahedral FeB＊ in the sub-nanostructured Fe304 film, which produces the high magnetization. Using soft X-ray magnetic circular dichroism and soft X-ray absorption, both at the Fe L3,2- and O K-edges, and supported by first-principles and charge-transfer multiple calculations, we observe an anomalous enhancement of double exchange, accompanied by a suppression of the superexchange interactions because of the spin-flipping mechanism via oxygen at the grain boundaries. Our result may open avenues for developing spin- manipulated giant magnetic Fe304-based compounds via nano-grain size control.展开更多
基金Supported by National Natural Science Foundation of China(21271007,10274073)Post-doctoral Research Start-up Funding of Anhui University of Architecture(K02553)
文摘A small fluctuation of the photon beam position will affect the intensity and polarization characteristics of synchrotron radiation （SR） when it enters an endstation through the related beamline. In this paper, by changing the electron orbit equilibrium position in the vertical direction, we have measured the corresponding changes in the absorption strength of the SR with a gold mesh in different chopper aperture positions. It is found that for three aperture positions, the absorption intensity of the gold mesh shows a good Gaussian distribution as the photon beam position moves, while the ratio of the SR intensity passing through the upper and lower apertures shows a monotonous variation. This suggests a new method for estimating the circular polarization degree of SR originating from the bending magnet based on our current measurement.
文摘The BL07U beamline is a new extreme ultraviolet and soft X-ray beamline housed in the Shanghai Synchrotron Radiation Facility. Beamlines are used in nano-resolved angle-resolved photoemission spectroscopy(nano-ARPES), spin-resolved angle-resolved photoemission spectroscopy(spin-ARPES), X-ray magnetic circular dichroism spectroscopy, and X-ray magnetic linear dichroism spectroscopy for certain scientific research. The BL07U beamline, which is based on a pair of elliptical polarized undulators and a variable-included-angle plane-grating monochromator, delivers circularly or linear polarized X-rays within the energy range of 50–2000 eV. The beamline features two branches: One dedicated to nano-ARPES,which has a minimum spot size of only ~ 200 nm, and another branch comprising spin-ARPES, a vector magnetic field, and superconductive magnetic end-station.
基金financial support from the Spanish Government,(Grants CTQ2012-32247,CTQ2015-68370-P)YL and WW acknowledge the EU for financial support within the FP7 FET-Proactive project MoQuaS No.610449for the Agence Nationale de la Recherche(France)for project MolQuSpin,No.ANR-13-BS10.
文摘A heterometallic Ni_(4)Tb field-induced SMM has been grafted onto the surface of superparamagnetic iron oxide nanoparticles.The magnetic coupling within the Ni_(4)Tb and between the Ni_(4)Tb and iron oxide nanoparticle has been studied by element specific XMCD measurements.The coupling between Ni and Tb is ferromagnetic and the complex remains intact when grafted onto the iron oxide nanoparticles.
基金European Union’s Horizon 2020 research and innovation program under grant agreement no.[766726]。
文摘The measurement of the magnetic anisotropy of[Fe{(3,5-(CH_(3))_(2)Pz)_(3)BH}_(2)],where Pz=pyrazole,in its high spin state(S=2)by X-ray Magnetic Circular Dichroism(XMCD)spectroscopy when assembled as an organized monolayer on Cu(111)shows the presence of a hard axis of magnetization(positive axial zero-field splitting-ZFS-parameter D).Combining magnetization and multifrequency electron paramagnetic resonance spectroscopy on a reference compound,[Fe{(3-(Ph)Pz)_(3)BH}_(2)],of the same family and ab initio wave function based theoretical calculations,we demonstrate that the magnetic anisotropy of the assembled molecules is not affected when they are present at the substrate/vacuum interface.Comparing our results with those of a reported complex having an almost identical FeN_(6)coordination sphere but an easy axis of magnetization(corresponding to a negative D value),we show that the nature of the magnetic anisotropy(easy/hard axis)is governed by the torsion angle(Ψ)defined by the relative orientation of the pyrazole five-membered rings to the pseudo three-fold axis of the molecules.The rigidity of the(Pz)_(3)BH tridentate ligands,where the three pyrazole moieties are held by the BH group,allows only very slight changes in the torsion angle even when the molecules are in a dissymmetric environment such as an interface.This is the origin of the robust magnetic anisotropy of this family of compounds.
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.
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.
基金This work was supported by the National Natural Science Foundation of China （Grant Nos. 10274073 ＆ 10435050）Innovation Foundation of the University of Science ＆ Technology of China （Grant No. KD2005055）.
文摘Co-Fe alloy films have such properties as high saturation magnetization, high Curie tem- perature and low coercive force. It is of importance to study the origin of high saturation magnetization in these alloys. In this paper, we study the spin (ms) and orbital moments (mo) of Fe and Co in the Co0.9Fe0.1 film by using X-ray magnetic circular dichroism (XMCD) and SQUID magnetometry. The ms and mo for Co are 1.58 and 0.31 μB, and for Fe are 1.63 and 0.36 μB respectively. The average magnetic moment (1.90 μB) determined by XMCD is in agreement with that obtained from SQUID measurements. The total magnetic moment ratio of Fe to Co is 10.5:89.5, while the ratio of the spin to orbital moment is 83.4:16.6. Considering the separation of the spin and orbital moment, an outcome of mFe-spin : mFe-orbit : mCo-spin : mCo-orbit = 8.6:1.9:74.8:14.7 is obtained.
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.
基金This work was supported by National Research Center(NRC)“Kurchatov Institute”(No.1359,characterization)the Russian Science Foundation(No.19-19-00009(synthesis)and No.20-79-10028(magnetization measurements))。
文摘Two-dimension(2D)magnets have recently developed into a class of stoichiometric materials with prospective applications in ultra-compact spintronics and quantum computing.Their functionality is particularly rich when different magnetic orders are competing in the same material.Metalloxenes REX2(RE=Eu,Gd;X=Si,Ge),silicene or germanene—heavy counterparts of graphene—coupled with a layer of rare-earth metals,evolve from three-dimension(3D)antiferromagnets in multilayer structures to 2D ferromagnets in a few monolayers.This evolution,however,does not lead to fully saturated 2D ferromagnetism,pointing at a possibility of coexisting/competing magnetic states.Here,REX2 magnetism is explored with element-selective X-ray magnetic circular dichroism(XMCD).The measurements are carried out for GdSi2,EuSi2,GdGe2,and EuGe2 of different thicknesses down to 1 monolayer employing K absorption edges of Si and Ge as well as M and L edges of the rare-earths.They access the magnetic state in REX2 and determine the seat of magnetism,orbital,and spin contributions to the magnetic moment.High-field measurements probe remnants of the bulk antiferromagnetism in 2D REX2.The results provide a new platform for studies of complex magnetic structures in 2D materials.
基金supported by the National Natural Science Foundation of China (51322207 and 51332001)Beijing Natural Science Foundation (2132023)the Fundamental Research Funds for the Central Universities (2012LYB07)
文摘In recent decades, magnetoelectric effect in multiferroic materials has attracted extensive attention owing to the upcoming demands for new-generation multi-functional magnetoelectronic devices, such as transducer, sensor and so on. This gives people a strong push to explore the multiferroic materials with a reduced dimension and effective coupling between electric and magnetic orderings, especially at room temperature. Due to the weak magnetoelectric coupling strength in sing-phase multiferroic materials, scientists start to design nanocomposites and artificial nanostructures with strong coupling among order parameters(lattice, charge, spin and orbital). In this review, we will introduce recent major progresses of magnetoelectric coupling in multiferroic nanocomposites across their interfaces from the following four aspects: strain effect, charge transfer, magnetic exchange interaction and orbital hybridization, based on their coupling mechanisms. Through a full understanding of the above coupling among these orderings, it is possible to achieve the nanoscale modulation of magnetization(ferroelectric polarization) by external electric(magnetic) field. Apart from the magnetoelectric coupling, those artificially functional nanocomposites provide us a platform to explore and study the emerging physical phenomena so that we can design self-assembled nanostructures to tailor novel functionalities in future applications.
基金supported by the National Natural Science Foundation of China (Grant No. 10274073)the Post-doctoral Research Start-up Funding of Anhui University of Architecture (Grant No. K02553)the Open Project of Building Energy Conservation Institute of Anhui University of Architecture (Grant No. K02592)
文摘Patterned ferromagnetic thin film shows promising applications in ultra-high density magnetic storage,magnetoresistive transducer,magnetic random access memory and many other devices.Since the performance of these devices is closely associated with the magnetic properties of the etched patterns,it is necessary to study the effects of freshly etched surface oxidation on the magnetic properties of the patterned microstructures.In the current work,were carried out an X-ray Magnetic Circular Dichroism(XMCD) study on a 50 nm Co 0.9 Fe 0.1 continuous thin film and a related patterned Co 0.9 Fe 0.1 grating structure etched with a 2 μm period.Based on the sum rules,the spin and orbital moments were calculated for these two samples,respectively.The results indicated that the spin and orbital moments of grating structure(1.34μ B and 0.24μ B,respectively) decreased 17.3% compared with the corresponding continuous film(1.62μ B and 0.29μ B,respectively).We proposed that the moment decreasing of the patterned grating structure was mainly caused by the etched surface oxidation during the pattern manufacture process.The oxidation ratio of Co element in the patterned grating structure is 14.4% calculated from X-ray absorption spectroscopy(XAS) measurement.Considering the oxidation ratio,we amend the spin and orbital moment of Co and the amended result is basically in accordance with that of continuous film,demonstrating that the difference of the spin and orbital moments between the sub-micron grating unit and the continuous film is really caused by the oxidation.
文摘Magnetite Fe304 （ferrite） has attracted considerable interest for its exceptional physical properties： It is predicted to be a semimetallic ferromagnetic with a high Curie temperature, it displays a metal-insulator transition, and has potential oxide-electronics applications. Here, we fabricate a high-magnetization （〉 1 Tesla） high-resistance （-0.1 Ωcm） sub-nanostructured （grain size 〈 3 nm） Fe304 film via grain-size control and nano-engineering. We report a new phenomenon of spin- flipping of the valence-spin tetrahedral FeB＊ in the sub-nanostructured Fe304 film, which produces the high magnetization. Using soft X-ray magnetic circular dichroism and soft X-ray absorption, both at the Fe L3,2- and O K-edges, and supported by first-principles and charge-transfer multiple calculations, we observe an anomalous enhancement of double exchange, accompanied by a suppression of the superexchange interactions because of the spin-flipping mechanism via oxygen at the grain boundaries. Our result may open avenues for developing spin- manipulated giant magnetic Fe304-based compounds via nano-grain size control.
