Disentanglement of magnetic contributions in multi‐component systems by using X‐ray magnetic circular dichroism at a single absorption edge

X‐ray magnetic circular dichroism (XMCD) has become in recent years an outstanding tool for studying magnetism. Its element specificity, inherent to core‐level spectroscopy, combined with the application of magneto‐optical sum rules allows quantitative magnetic measurements at the atomic level. These capabilities are now incorporated as a standard tool for studying the localized magnetism in many systems. However, the application of XMCD to the study of the conduction‐band magnetism is not so straightforward. Here, it is shown that the atomic selectivity is not lost when XMCD probes the delocalized states. On the contrary, it provides a direct way of disentangling the magnetic contributions to the conduction band coming from the different elements in the material. This is demonstrated by monitoring the temperature dependence of the XMCD spectra recorded at the rare‐earth L₂‐edge in the case of RT₂ (R = rare‐earth, T = 3d transition metal) materials. These results open the possibility of performing element‐specific magnetometry by using a single X‐ray absorption edge.     

X‐Treme beamline at SLS: X‐ray magnetic circular and linear dichroism at high field and low temperature

X‐Treme is a soft X‐ray beamline recently built in the Swiss Light Source at the Paul Scherrer Institut in collaboration with École Polytechnique Fédérale de Lausanne. The beamline is dedicated to polarization‐dependent X‐ray absorption spectroscopy at high magnetic fields and low temperature. The source is an elliptically polarizing undulator. The end‐station has a superconducting 7 T–2 T vector magnet, with sample temperature down to 2 K and is equipped with an in situ sample preparation system for surface science. The beamline commissioning measurements, which show a resolving power of 8000 and a maximum flux at the sample of 4.7 × 10¹² photons s^?1, are presented. Scientific examples showing X‐ray magnetic circular and X‐ray magnetic linear dichroism measurements are also presented.     

Temperature dependence of the Ho L2‐edge XMCD spectra of Ho6Fe23

An X‐ray magnetic circular dichroism (XMCD) study performed at the Ho L_2,3‐edges in Ho₆Fe₂₃ as a function of temperature is presented. It is demonstrated that the anomalous temperature dependence of the Ho L₂‐edge XMCD signal is due to the magnetic contribution of Fe atoms. By contrast, the Ho L₃‐edge XMCD directly reflects the temperature dependence of the Ho magnetic moment. By combining the XMCD at both Ho L₂‐ and L₃‐edges, the possibility of determining the temperature dependence of the Fe magnetic moment is demonstrated. Then, both μ_Ho(T) and μ_Fe(T) have been determined by tuning only the absorption L‐edges of Ho. This result opens new possibilities of applying XMCD at these absorption edges to obtain quantitative element‐specific magnetic information that is not directly obtained by other experimental tools.     

A compact permanent‐magnet system for measuring magnetic circular dichroism in resonant inelastic soft X‐ray scattering

A compact and portable magnet system for measuring magnetic dichroism in resonant inelastic soft X‐ray scattering (SX‐RIXS) has been developed at the beamline BL07LSU in SPring‐8. A magnetic circuit composed of Nd–Fe–B permanent magnets, which realised ～0.25 T at the center of an 11 mm gap, was rotatable around the axis perpendicular to the X‐ray scattering plane. Using the system, a SX‐RIXS spectrum was obtained under the application of the magnetic field at an angle parallel, nearly 45° or perpendicular to the incident X‐rays. A dedicated sample stage was also designed to be as compact as possible, making it possible to perform SX‐RIXS measurements at arbitrary incident angles by rotating the sample stage in the gap between the magnetic poles. This system enables facile studies of magnetic dichroism in SX‐RIXS for various experimental geometries of the sample and the magnetic field. A brief demonstration of the application is presented.     

Element‐selective X‐ray detected magnetic resonance: a novel application of synchrotron radiation

X‐ray detected magnetic resonance (XDMR) is a new element‐selective spectroscopy in which X‐ray magnetic circular dichroism is used to probe the resonant precession of spin and orbital magnetization components when a strong microwave pump field is applied perpendicularly to the static bias field. Experimental configurations suitable for detecting the very weak XDMR signal are compared. XDMR signatures were measured in yttrium iron garnet and related thin films on exciting not only the iron K‐edge but also the yttrium at diamagnetic sites. These measurements are shown to yield unique information regarding the wide‐angle precession of induced magnetization components involving either orbital p‐projected densities of states at the iron sites, or spin polarized d‐projected densities of states at the yttrium sites. Extending XDMR measurements into the millimeter wave range would make it possible to study paramagnetic systems routinely and investigate optical modes as well as acoustic modes in ferrimagnetic/antiferromagnetic systems.     

Design and performance of BOREAS,the beamline for resonant X‐ray absorption and scattering experiments at the ALBA synchrotron light source

The optical design of the BOREAS beamline operating at the ALBA synchrotron radiation facility is described. BOREAS is dedicated to resonant X‐ray absorption and scattering experiments using soft X‐rays, in an unusually extended photon energy range from 80 to above 4000 eV, and with full polarization control. Its optical scheme includes a fixed‐included‐angle, variable‐line‐spacing grating monochromator and a pair of refocusing mirrors, equipped with benders, in a Kirkpatrick–Baez arrangement. It is equipped with two end‐stations, one for X‐ray magnetic circular dichroism and the other for resonant magnetic scattering. The commissioning results show that the expected beamline performance is achieved both in terms of energy resolution and of photon flux at the sample position.     

Single‐crystal X‐ray diffraction and resonant X‐ray magnetic scattering at helium‐3 temperatures in high magnetic fields at beamline P09 at PETRA III

The resonant scattering and diffraction beamline P09 at PETRA III at DESY is equipped with a 14 T vertical field split‐pair magnet. A helium‐3 refrigerator is available that can be fitted inside the magnet's variable‐temperature insert. Here the results of a series of experiments aimed at determining the beam conditions permitting operations with the He‐3 insert are presented. By measuring the tetragonal‐to‐orthorhombic phase transition occurring at 2.1 K in the Jahn–Teller compound TmVO₄, it is found that the photon flux at P09 must be attenuated down to 1.5 × 10⁹ photons s^?1 for the sample to remain at temperatures below 800 mK. Despite such a reduction of the incident flux and the subsequent use of a Cu(111) analyzer, the resonant X‐ray magnetic scattering signal at the Tm L_III absorption edge associated with the spin‐density wave in TmNi₂B₂C below 1.5 K is intense enough to permit a complete study in magnetic field and at sub‐Kelvin temperatures to be carried out.     

Spin-polarization and x-ray magnetic circular dichroism in GaAs

The combination of angular spin momentum with electronics is a promising successor to charge-based electronics. The conduction bands in GaAs may become spin-polarized via optical spin pumping, doping with magnetic ions, or induction of a moment with an external magnetic field. We investigated the spin populations in GaAs with x-ray magnetic circular dichroism for each of these three cases. We find strong anti-symmetric lineshapes at the Ga L₃ edge indicating conduction band spin splitting, with differences in line width and amplitude depending on the source of spin polarization.     

X‐ray spectromicroscopy with the scanning transmission X‐ray microscope at BESSY II

Using the scanning transmission X‐ray microscope at BESSY II, colloidal structures from a Chernozem soil have been studied with a spatial resolution around 60 nm and a spectral resolution of 1700 at the K‐absorption edge of carbon. Elemental mapping has been used to determine the distribution of organic matter within the colloidal structures. Spectra have been extracted from image stacks to obtain information about the chemical state. For the analysis of the latter, principal component analysis and cluster analysis have been applied. It was possible, for example, to discriminate clay particles against organic components.     

A microfocus X‐ray fluorescence beamline at Indus‐2 synchrotron radiation facility

A microfocus X‐ray fluorescence spectroscopy beamline (BL‐16) at the Indian synchrotron radiation facility Indus‐2 has been constructed with an experimental emphasis on environmental, archaeological, biomedical and material science applications involving heavy metal speciation and their localization. The beamline offers a combination of different analytical probes, e.g. X‐ray fluorescence mapping, X‐ray microspectroscopy and total‐external‐reflection fluorescence characterization. The beamline is installed on a bending‐magnet source with a working X‐ray energy range of 4–20 keV, enabling it to excite K‐edges of all elements from S to Nb and L‐edges from Ag to U. The optics of the beamline comprises of a double‐crystal monochromator with Si(111) symmetric and asymmetric crystals and a pair of Kirkpatrick–Baez focusing mirrors. This paper describes the performance of the beamline and its capabilities with examples of measured results.     

Simultaneous X‐ray fluorescence and scanning X‐ray diffraction microscopy at the Australian Synchrotron XFM beamline

Owing to its extreme sensitivity, quantitative mapping of elemental distributions via X‐ray fluorescence microscopy (XFM) has become a key microanalytical technique. The recent realisation of scanning X‐ray diffraction microscopy (SXDM) meanwhile provides an avenue for quantitative super‐resolved ultra‐structural visualization. The similarity of their experimental geometries indicates excellent prospects for simultaneous acquisition. Here, in both step‐ and fly‐scanning modes, robust, simultaneous XFM‐SXDM is demonstrated.     

X‐ray magnetic spectroscopy at high pressure: performance of SPring‐8 BL39XU

An X‐ray magnetic circular dichroism experiment under multiple extreme conditions, 2 ≤T≤ 300 K, H≤ 10 T and P≤ 50 GPa, has been achieved at SPring‐8 BL39XU. A combination of the high‐brilliant X‐ray beam and a helicity‐controlled technique enabled the dichroic signal to be recorded with high accuracy. The performance is shown by the outcome of pressure‐induced ferromagnetism in Mn₃GaC and the pressure‐suppressed Co moment in ErCo₂. Two technical developments, a tiny diamond anvil cell inserted into a superconducting magnet and in situ pressure calibration using 90° Bragg diffraction from a NaCl marker, are also presented. X‐ray magnetic spectroscopy under multiple extreme conditions is now opening a new approach to materials science.     

Diffractive–refractive optics: (+,−,−,+) X‐ray crystal monochromator with harmonics separation

A new kind of two channel‐cut crystals X‐ray monochromator in dispersive (+,?,?,+) position which spatially separates harmonics is proposed. The diffracting surfaces are oriented so that the diffraction is inclined. Owing to refraction the diffracted beam is sagittally deviated. The deviation depends on wavelength and is much higher for the first harmonics than for higher harmonics. This leads to spatial harmonics separation. The idea is supported by ray‐tracing simulation.     

Soft X‐ray absorption spectroscopy and resonant inelastic X‐ray scattering spectroscopy below 100 eV: probing first‐row transition‐metal M‐edges in chemical complexes

X‐ray absorption and scattering spectroscopies involving the 3d transition‐metal K‐ and L‐edges have a long history in studying inorganic and bioinorganic molecules. However, there have been very few studies using the M‐edges, which are below 100 eV. Synchrotron‐based X‐ray sources can have higher energy resolution at M‐edges. M‐edge X‐ray absorption spectroscopy (XAS) and resonant inelastic X‐ray scattering (RIXS) could therefore provide complementary information to K‐ and L‐edge spectroscopies. In this study, M_2,3‐edge XAS on several Co, Ni and Cu complexes are measured and their spectral information, such as chemical shifts and covalency effects, are analyzed and discussed. In addition, M_2,3‐edge RIXS on NiO, NiF₂ and two other covalent complexes have been performed and different d–d transition patterns have been observed. Although still preliminary, this work on 3d metal complexes demonstrates the potential to use M‐edge XAS and RIXS on more complicated 3d metal complexes in the future. The potential for using high‐sensitivity and high‐resolution superconducting tunnel junction X‐ray detectors below 100 eV is also illustrated and discussed.     

Adaption of a diffractometer for time‐resolved X‐ray resonant magnetic scattering

A new set‐up is presented to measure element‐selective magnetization dynamics using the ALICE chamber [Grabis et al. (2003), Rev. Sci. Instrum. 74 , 4048–4051] at the BESSY II synchrotron at the Helmholtz‐Zentrum Berlin. A magnetic‐field pulse serves as excitation, and the magnetization precession is probed by element‐selective X‐ray resonant magnetic scattering. With the use of single‐bunch‐generated X‐rays a temporal resolution well below 100 ps is reached. The ALICE diffractometer environment enables investigations of thin films, described here, multilayers and laterally structured samples in reflection or diffuse scattering geometry. The combination of the time‐resolved set‐up with a cryostat in the ALICE chamber will allow temperature‐dependent studies of precessional magnetization dynamics and of damping constants to be conducted over a large temperature range and for a large variety of systems in reflection geometry.     

Polarization control of an X‐ray free‐electron laser with a diamond phase retarder

A diamond phase retarder was applied to control the polarization states of a hard X‐ray free‐electron laser (XFEL) in the photon energy range 5–20 keV. The horizontal polarization of the XFEL beam generated from the planar undulators of the SPring‐8 Angstrom Compact Free‐Electron Laser (SACLA) was converted into vertical or circular polarization of either helicity by adjusting the angular offset of the diamond crystal from the exact Bragg condition. Using a 1.5 mm‐thick crystal, a high degree of circular polarization, 97%, was obtained for 11.56 keV monochromatic X‐rays, whereas the degree of vertical polarization was 67%, both of which agreed with the estimations including the energy bandwidth of the Si 111 beamline monochromator.     

X‐ray powder diffraction at the XRD1 beamline at LNLS

Various upgrades have been completed at the XRD1 beamline at the Brazilian synchrotron light source (LNLS). The upgrades are comprehensive, with changes to both hardware and software, now allowing users of the beamline to conduct X‐ray powder diffraction experiments with faster data acquisition times and improved quality. The main beamline parameters and the results obtained for different standards are presented, showing the beamline ability of performing high‐quality experiments in transmission geometry. XRD1 operates in the 5.5–14 keV range and has a photon flux of 7.8 × 10⁹ photons s^?1 (with 100 mA) at 12 keV, which is one of the typical working energies. At 8 keV (the other typical working energy) the photon flux at the sample position is 3.4 × 10¹⁰ photons s^?1 and the energy resolution ΔE/E = 3 × 10^?4.     

XDS: a flexible beamline for X‐ray diffraction and spectroscopy at the Brazilian synchrotron

The majority of the beamlines at the Brazilian Synchrotron Light Source Laboratory (LNLS) use radiation produced in the storage‐ring bending magnets and are therefore currently limited in the flux that can be used in the harder part of the X‐ray spectrum (above ～10 keV). A 4 T superconducting multipolar wiggler (SCW) was recently installed at LNLS in order to improve the photon flux above 10 keV and fulfill the demands set by the materials science community. A new multi‐purpose beamline was then installed at the LNLS using the SCW as a photon source. The XDS is a flexible beamline operating in the energy range between 5 and 30 keV, designed to perform experiments using absorption, diffraction and scattering techniques. Most of the work performed at the XDS beamline concentrates on X‐ray absorption spectroscopy at energies above 18 keV and high‐resolution diffraction experiments. More recently, new setups and photon‐hungry experiments such as total X‐ray scattering, X‐ray diffraction under high pressures, resonant X‐ray emission spectroscopy, among others, have started to become routine at XDS. Here, the XDS beamline characteristics, performance and a few new experimental possibilities are described.     

Implementation of ultrafast X‐ray diffraction at the 1W2B wiggler beamline of Beijing Synchrotron Radiation Facility

The implementation of a laser pump/X‐ray probe scheme for performing picosecond‐resolution X‐ray diffraction at the 1W2B wiggler beamline at Beijing Synchrotron Radiation Facility is reported. With the hybrid fill pattern in top‐up mode, a pixel array X‐ray detector was optimized to gate out the signal from the singlet bunch with interval 85 ns from the bunch train. The singlet pulse intensity is ～2.5 × 10⁶ photons pulse^?1 at 10 keV. The laser pulse is synchronized to this singlet bunch at a 1 kHz repetition rate. A polycapillary X‐ray lens was used for secondary focusing to obtain a 72 µm (FWHM) X‐ray spot. Transient photo‐induced strain in BiFeO₃ film was observed at a ～150 ps time resolution for demonstration.     

X‐ray photon correlation spectroscopy in systems without long‐range order: existence of an intermediate‐field regime

Successful X‐ray photon correlation spectroscopy studies often require that signals be optimized while minimizing power density in the sample to decrease radiation damage and, at free‐electron laser sources, thermal impact. This suggests exploration of scattering outside the Fraunhofer far‐field diffraction limit d²/λR, where d is the incident beam size, λ is the photon wavelength and R is the sample‐to‐detector distance. Here it is shown that, in an intermediate regime d²/λ > Rdξ/λ, where ξ is the structural correlation length in the material, the ensemble averages of the scattered intensity and of the structure factor are equal. Similarly, in the regime d²/λ > Rdξ(τ)/λ, where ξ(τ) is a time‐dependent dynamics length scale of interest, the ensemble‐averaged correlation functions g₁(τ) and g₂(τ) of the scattered electric field are also equal to their values in the far‐field limit. This broadens the parameter space for X‐ray photon correlation spectroscopy experiments, but detectors with smaller pixel size and variable focusing are required to more fully exploit the potential for such studies.