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The CeB6(001) single crystal used as a cathode in a low-emittance electron gun and operated at the free-electron laser facility SACLA was investigated using cathode lens electron microscopy combined with X-ray spectroscopy at SPring-8 synchrotron radiation facility. Multilateral analysis using thermionic emission electron microscopy, low-energy electron microscopy, ultraviolet and X-ray photoemission electron microscopy and hard X-ray photoemission spectroscopy revealed that the thermionic electrons are emitted strongly and evenly from the CeB6 surface after pre-activation treatment (annealing at 1500°C for >1 h) and that the thermionic emission intensity as well as elemental composition vary between the central area and the edge of the old CeB6 surface.

Recently, all-optical magnetization control has been garnering considerable attention in realizing next-generation ultrafast magnetic information devices. Here, employing a magneto-optical Kerr effect (MOKE) microscope, we observed the laser-induced magnetization switching of ferrimagnetic oxide NiCo2O4 (NCO) epitaxial thin films with perpendicular magnetic anisotropy, where the sample was pumped at 1030-nm laser pulses, and magnetic domain images were acquired via the MOKE microscope with a white light emitting diode. Laser pulses irradiated an NCO thin film at various temperatures from 300 K to 400 K while altering the parameters of pulse interval, fluence, and the number of pulses with the absence of the external magnetic field. We observed accumulative all-optical switching at 380 K and above. Our observation of oxide NCO thin films facilitates the realization of chemically stable magnetization switching using ultrafast lasers, and without applying a magnetic field., Comment: 6 pages, 6 figures

Recent progress in materials informatics has triggered growing interest in combinatorial experimental systems for materials development. We demonstrate a novel high-throughput experiment combining compact materials synthesis, synchrotron radiation measurements, and statistical data analysis. This technique focuses on not only drawing phase diagrams but also analysing phase transitions for exploring the functions of magnetic materials. This study involved the rapid preparation of a composition-gradient Fe–Co–Cr ternary thin film using a table-top sputtering system and 3D printer, followed by measurement of the chemical components and magnetic contrast by photoemission electron microscopy, through the acquisition of one million spectral datasets within 10 min. The ternary magnetic phase diagram of Fe–Co–Cr obtained by statistical analysis of the magnetic circular dichroism (MCD) contrast images was in perfect agreement with previous studies. The MCD histogram was fitted based on Landau theory, and the estimated critical exponent β (0.36 ± 0.028) showed excellent agreement with previous theoretical and experimental studies. This study successfully demonstrates universal physical parameter analysis that characterizes magnetic properties by a high-throughput approach combined with a simple experimental apparatus.

Recently, ferroelectric semiconductors has become a subject of interest with regard to potential applications in novel electronic and opto-electric devices. One of the most important aspects of employing these materials is band modulation based on spontaneous polarization to generate polarization charges acting as quasi-dopants at metal/ferroelectric and ferroelectric/ferroelectric interfaces. The present study fabricated graphene/Mn-doped BiFeO3 (BFMO)/SrRuO3/SrTiO3(001) capacitor structures with the BFMO having either upward or downward polarization. Band modulation at the graphene/BFMO interface as a result of polarization charges was evaluated using photoemission electron microscopy on the BL17SU beamline at the SPring-8 facility, Japan. The chemical shifts observed in Bi 4f and C 1s XPS spectra indicated that positive (negative) polarization charges acted as quasi-dopants for electron (hole) doping of the BFMO and graphene.

The CeB

An endstation dedicated to angle-resolved photoemission spectroscopy (ARPES) using a soft X-ray microbeam has been developed at the beamline BL25SU of SPring-8. To obtain a high photoemission intensity, this endstation is optimized for measurements under the condition of grazing beam incidence to a sample surface, where the glancing angle is 5° or smaller. A Wolter mirror is used for focusing the soft X-rays. Even at the glancing angle of 5°, the smallest beam spot still having a sufficient photon flux for ARPES is almost round on the sample surface and the FWHM diameter is ∼5 µm. There is no need to change the sample orientation for performing k x − k y mapping by virtue of the electron lens with a deflector of the photoelectron analyzer, which makes it possible to keep the irradiation area unchanged. A partially cleaved surface area as small as ∼20 µm was made on an Si(111) wafer and ARPES measurements were performed. The results are presented.

The competition between magnetic shape anisotropy and the induced uniaxial magnetic anisotropy in the heterojunction between a ferromagnetic layer and a ferroelectric substrate serves to control magnetic domain structures as well as magnetization reversal characteristics. The uniaxial magnetic anisotropy, originating from the symmetry breaking effect in the heterojunction, plays a significant role in modifying the characteristics of magnetization dynamics. Magnetoelastic phenomena are known to generate uniaxial magnetic anisotropy, however, the interfacial electronic states that may contribute to the uniaxial magnetic anisotropy have not yet been adequately investigated. Here, we report experimental evidence concerning the binding energy change in the ferromagnetic layer/ferroelectric substrate heterojunction using X-ray photoemission spectroscopy. The binding energy shifts, corresponding to the chemical shifts, reveal the binding states near the interface. Our results shed light on the origin of the uniaxial magnetic anisotropy induced from the heterojunction. This knowledge can provide a means for the simultaneous control of magnetism, mechanics, and electronics in a nano/microsystem consisting of ferromagnetic/ferroelectric materials.

Graphene is promising for next-generation devices. However, one of the primary challenges in realizing these devices is the scalable growth of high-quality few-layer graphene (FLG) on device-type wafers, it is difficult to do so while balancing both quality and affordability. High-quality graphene is grown on expensive SiC bulk crystals, while graphene on SiC thin films grown on Si substrates (GOS) exhibits low quality but affordable cost. We propose a new method for the growth of high-quality FLG on a new template named “hybrid SiC”. The hybrid SiC is produced by bonding a SiC bulk crystal with an affordable device-type wafer and subsequently peeling off the SiC bulk crystal to obtain a single-crystalline SiC thin film on the wafer. The quality of FLG on this hybrid SiC is comparable to that of FLG on SiC bulk crystals and much higher than of GOS. FLG on the hybrid SiC exhibited high carrier mobilities, comparable to those on SiC bulk crystals, as anticipated from the linear band dispersions. Transistors using FLG on the hybrid SiC showed the potential to operate in terahertz frequencies. The proposed method is suited for growing high-quality FLG on desired substrates with the aim of realizing graphene-based high-speed devices.

We report magnetic domain formation control within micro-scale polycrystalline Ni wires on a single-crystal Y-cut 128° LiNbO3 substrate. X-ray magnetic circular dichroism photoemission electron microscopy (XCDM-PEEM), micromagnetic simulations, and magnetoresistance (MR) measurements allowed us to estimate the uniaxial magnetic anisotropy induced by the magnetoelastic effect that originated at the interface between each Ni layer and the LiNbO3 substrate. Comparison of the XMCD-PEEM and MR measurement results shows that the competition between the shape magnetic anisotropy and the uniaxial magnetic anisotropy parallel to the orientation flat (OF) direction of the substrate leads to variations in both the magnetization order and the magnetization reversal process. The uniaxial magnetic anisotropy is estimated to be approximately 3.3 kJ/m3. This heterojunction structure composed of ferromagnetic and ferroelectric layers thus offers alternative ways to produce artificial functional multiferroic materials and devices.

Two types of optical choppers for time-resolved measurements in soft X-ray beamlines of synchrotron radiation facilities were developed, which are utilized under ultra-high-vacuum conditions., Two types of optical choppers for time-resolved measurements at synchrotron radiation soft X-ray beamlines have been developed. One type uses an air-spindle-type rotation mechanism with a two-stage differential pumping system to maintain the ultra-high vacuum of the X-ray beamline, and the other uses a magnetic bearing. Both can be installed at the soft X-ray beamlines at SPring-8, greatly improving the accessibility of pump-and-probe spectroscopy. The combination of X-ray chopper and pump-and-probe photoemission electron microscope at SPring-8 provides drastic improvements in signal-to-noise ratio and resolution compared with techniques using high-voltage gating of channel plate detectors. The choppers have the capability to be used not only at synchrotron radiation facilities but also at other types of soft X-ray and VUV beamlines.

The charging effect often complicates photoemission spectroscopy and x-ray absorption spectroscopy of an insulating material. Here, monolayer graphene was used as a conductive layer to prevent the charging effect of insulating substrates such as glass and LiNbO3. Charging-free spectra were obtained with various photon energies ranging from vacuum ultraviolet light to hard x-rays. This method could also be applied to photoemission spectroscopy of epoxy adhesives and to photoemission electron microscopy of an insulating film. Photoelectron transmissivities for the transferred graphene film were evaluated over a wide kinetic energy range from 29 to 7910 eV. A minimum transmissivity of ∼0.1 was found at a kinetic energy of ∼60 eV, which rose to 0.86 at 7910 eV. In terms of the kinetic energy dependence of the transmissivity, this method is especially suitable for conventional and hard x-ray photoelectron spectroscopy.

For a long time, there were no efficient ways of controlling antiferromagnets. Quite a strong magnetic field was required to manipulate the magnetic moments because of a high molecular field and a small magnetic susceptibility. It was also difficult to detect the orientation of the magnetic moments since the net magnetic moment is effectively zero. For these reasons, research on antiferromagnets has not been progressed as drastically as that on ferromagnets which are the main materials in modern spintronic devices. Here we show that the magnetic moments in NiO, a typical natural antiferromagnet, can indeed be controlled by the spin torque with a relatively small electric current density (~4 × 107 A/cm2) and their orientation is detected by the transverse resistance resulting from the spin Hall magnetoresistance. The demonstrated techniques of controlling and detecting antiferromagnets would outstandingly promote the methodologies in the recently emerged “antiferromagnetic spintronics”. Furthermore, our results essentially lead to a spin torque antiferromagnetic memory.

Grain-oriented Fe-3%Si steels are industrially important soft magnetic materials that are usually used in transformer cores but have also recently started to be used in motor cores [1]. Further improvements in the magnetic properties of grain-oriented steels are required to increase the efficiency of electrical machinery. The magnetic properties of grain-oriented steels strongly depend on the magnetic domain structures. The magnetic domains in grain-oriented steels mainly consist of the 180° basic domains and supplementary domains, such as lancet domains. The lancet domains, which occur due to a tilt angle of the [001] easy axis out of the steel surface (β), affect not only iron losses but also magnetostrictive noise. Therefore, it is important to understand the behavior of the lancet domains in order to further improve the magnetic properties. Many studies of the lancet domains [2-4] have been performed, for example, under applied stresses and external magnetic fields at the room temperature (RT). However, the behavior of lancet domains in the region above RT has not yet been investigated even though the operating temperature of transformers and electric motors are generally above RT. In this paper, the changes in the lancet domains of grain-oriented steels over the range from RT to the Curie point were observed using photoemission electron microscopy combined with X-ray magnetic circular dichroism (XMCD-PEEM). Moreover, the domain theory enabled us to quantitatively explain the observed temperature dependence of the lancet domains.

We demonstrated control of magnetic domain structure formation within micro-scale polycrystalline Ni wires fabricated on a single crystalline LiNbO3 substrate. We observed the domain structures using X-ray magnetic circular dichroism-photoemission electron microscopy at SPring-8 BL25SU and BL17SU. Both zebra-stripe domain and ordinary single domain structures can be formed in the Ni wire in control of alignment of the wire onto the substrate. The result suggests that magnetoelastic effects from pizoelectristic substrates can strongly influence the magnetization alignment, overwhelming their shape magnetic anisotropy. The formation of zebra-stripe domain structure can be qualitatively explained by the micromagnetic simulation under the assumption of the magnetic anisotropy perpendicular to the longitudinal axis of wire. Our finding provides a way to control the domain structure and magnetization reversal using the combination of shape magnetic anisotropy and strain-induced anisotropy.

The 3-D structures of the 90° closure domains in demagnetized Fe3%Si(110) steels occurring by the compressive stress were quantitatively analyzed using domain theory. The dependence of the compressive stress and the thickness in the 90° closure domains were evaluated using the proposed closure domain model with the 90° domain width. It was revealed that the 90° closure domain width decreases with an increase in compressive stress and steeply increases with a decrease in compressive stress. Moreover, our calculations predict that the critical compressive stress for the occurrence of the closure domains increase with the decrease in specimen thickness. The results suggest that when the thickness becomes thinner, enhancement of local compressive stress may be needed to refine 180° basic domains along the rolling direction. The validity of the calculation was confirmed by comparison with the past data and our presented domain observations by photoemission electron microscopy combined with X-ray magnetic circular dichroism.

FeNi with the L10-ordered structure is formed over an astronomical timescale in meteorites. In this study, severe plastic deformation using high-pressure torsion (HPT) is employed for the production of the L10 structure in the laboratory. Its formation is confirmed by X-ray diffraction analysis and transmission electron microscopy. Processing of elemental nanopowders by HPT is an effective method for the formation of the L10 phase, which is enhanced by the addition of Co to FeNi or annealing after HPT. The formation of the phase must be associated with enhanced diffusion through HPT.

The effect that grain size has on magnetization in cobalt substituted NiZn polycrystalline bulk ferrite has been studied and the magnetic domain has been visualized by taking measurements with a Photoemission Electron Microscope (PEEM). Complex permeability shows that magnetization with a grain size smaller than ~6 μm is dominated only by the spin rotation and the magnetic domain wall motion contributes when the grain size is larger. PEEM measurements show that the small grain induces the small magnetic domain and it becomes larger when the grain is large, which is a result that agrees with the magnetization process. At the same time, the presence of a domain wall across the grain boundary has been confirmed regardless of the grain size. This suggests the possibility of there being a magnetic coupling between the grains related to the effect that the microstructure has on magnetic domain structure and magnetization in cobalt substituted NiZn ferrite.

The mechanism of dense vertically aligned carbon nanotube growth achieved by a recently developed thermal chemical vapor deposition method was studied using synchrotron radiation spectroscopic techniques., The mechanism of the one-order-of-magnitude increase in the density of vertically aligned carbon nanotubes (CNTs) achieved by a recently developed thermal chemical vapor deposition process was studied using synchrotron radiation spectroscopic techniques. In the developed process, a Ti film is used as the underlayer for an Fe catalyst film. A characteristic point of this process is that C2H2 feeding for the catalyst starts at a low temperature of 450°C, whereas conventional feeding temperatures are ∼800°C. Photoemission spectroscopy using soft and hard X-rays revealed that the Ti underlayer reduced the initially oxidized Fe layer at 450°C. A photoemission intensity analysis also suggested that the oxidized Ti layer at 450°C behaved as a support for nanoparticle formation of the reduced Fe, which is required for dense CNT growth. In fact, a CNT growth experiment, where the catalyst chemical state was monitored in situ by X-ray absorption spectroscopy, showed that the reduced Fe yielded a CNT forest at 450°C. Contrarily, an Fe layer without the Ti underlayer did not yield such a CNT forest at 450°C. Photoemission electron microscopy showed that catalyst annealing at the conventional feeding temperature of 800°C caused excess catalyst agglomeration, which should lead to sparse CNTs. In conclusion, in the developed growth process, the low-temperature catalyst activation by the Ti underlayer before the excess Fe agglomeration realised the CNT densification.

Amongst the most interesting phenomena in correlated oxide systems are the doping-driven competitions between energetically similar ground states found in, e.g., high-Tc superconductors and colossal magnetoresistance manganites. It has recently been reported that doped multiferroics also exhibit this generic concept of phase competition. Here, we employ photoelectron emission microscopy (PEEM) to demonstrate evidence of systematic changes in the electronic structure of Bi(1-x)Ca(x)FeO(3-δ) treated by electrically controlled hole carrier doping, the outcome of which clearly correlates with the local modulation of electronic conductivity observed in the same material.

Unraveling the origin of ultrafast demagnetization in multisublattice ferromagnetic materials requires femtosecond x-ray techniques to trace the magnetic moment dynamics on individual elements, but this could not yet be achieved in the hard x-ray regime. We demonstrate here the first ultrafast demagnetization dynamics in the ferromagnetic heavy 5d-transition metal Pt using circularly-polarized hard x-rays at an x-ray free electron laser (XFEL). The decay time of laser-induced demagnetization of L10-FePt is determined to be τ Pt = 0.61 ± 0.04 ps using time-resolved x-ray magnetic circular dichroism at the Pt L3 edge, whereas magneto-optical Kerr measurements indicate the decay time for the total magnetization as τ total < 0.1 ps . A transient magnetic state with a photo-modulated ratio of the 3d and 5d magnetic moments is demonstrated for pump–probe delays larger than 1 ps. We explain this distinct photo-modulated transient magnetic state by the induced-moment behavior of the Pt atom and the x-ray probing depth. Our findings pave the way for the future use of XFELs to disentangle atomic spin dynamics contributions.

The angular distributions of photoelectrons and Auger electrons from single crystal surfaces show characteristic diffraction patterns, which contain information on the local atomic structures surrounding the emitter atoms. Using computational reconstruction processes on the diffraction patterns enables us to determine the local atomic structures of, for example, dopants, catalytic active sites, and surface/interface structures. This method has become known as "photoelectron holography (PEH)". Several advanced photoelectron analyzers for PEH are now available at beamlines at SPring-8, the world's largest synchrotron radiation facility. Recently, the use of micron-sized photon beams, as well as pump-and-probe time-resolved techniques has become possible with relatively high energy resolution. Here, the experimental apparatus and some representative applications are introduced.

A photoemission electron microscope (PEEM) system has been newly installed at the soft X-ray undulator beamline (BL17SU) of SPring-8 to realize time-resolved nanospectroscopy for the local transient electronic structures of advanced materials. This PEEM is a versatile machine composed of an electrostatic lens system and is intended for use in specific experiments such as time-resolved measurements. Pump–probe measurements in tandem with a femtosecond pulsed-laser system and an X-ray chopper are now readily available.

This study aims to investigate the creep motion of a magnetic domain wall (DW) induced by spin-Hall torque (SHT) in a Ta/Co–Ni/Pt hetero-structured thin wire using photoemission electron microscopy. The displacement of the DW was recorded every time after the duration of an electric current pulse. Results revealed that the existence of pinning centers and the inhomogeneity of the thermal diffusion property of the wire may result in an unstable DW motion. On the contrary, this data also suggested that the SHT induced from both the Ta and Pt layers can significantly improve the DW velocity, which was found to be three orders of magnitude larger than that previously reported for the MgO/Co–Ni/Pt system (Taniguchi et al., Appl. Phys. Exp. 7, 053005 (2014)).

The fusion of graphene with silicon may provide an effective solution to the problem of scale in electronic devices. This approach will allow the excellent electronic properties of graphene to be combined with known Si device technologies. We review the epitaxial growth of graphene on Si substrates (GOS) for fabricating transistors. GOS has been multifunctionalized by controlling the orientation of the Si substrate. The site-selective epitaxy of GOS has also been developed by controlling the base SiC thin films. These results demonstrate that GOS is suitable for integrated devices.

The multiferroic $\mathrm{BiFe}{\mathrm{O}}_{3}$ (BFO) as a charge-transfer-type insulator is an interesting system in which to explore correlated electronic conduction. Here, we substitute divalent Ca ions into the parent BFO and apply an external electric field at elevated temperatures to spatially redistribute spontaneously created oxygen vacancies, thereby generating hole carriers in regions of less dense oxygen-vacancy concentrations. X-ray diffraction and photoemission spectroscopic measurement are employed to quantify a large variation of local oxygen-vacancy concentration, as much as $\ensuremath{\sim}{10}^{21}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}3}$, and explore the consequent evolution of electronic band structure. We find that a nonrigid polaronic band is created by hole doping as a result of a strong electron-lattice coupling. We also show strong evidence for the disorder-driven formation of a Coulomb-glass state through electronic transport measurements on a quantitative level. These spectroscopic and transport results can be combined and understood in the framework of intrinsic spatial inhomogeneity of the polaronic charge density. The finding not only offers a promising platform and methodology for examining the interplay of functional defects and correlated electronic behaviors, but also suggests a unique electronic conduction mechanism applicable to systems with coexistence of strong electron correlation, electron-lattice interaction, and randomness beyond the Coulomb-glass physics in semiconductors.

Substantial upgrades have been made to the beamline BL25SU at SPring-8 for soft X-ray imaging and spectroscopy of solid-state materials. The upgraded beamline consists of two branches: a micro-beam branch with high energy resolution, and a nano-beam branch with small angular divergence. The beamline has been available for use since October 2014, following a half year commissioning period. We present here the beamline performance parameters, including resolving power, photon flux, and focused beam size, which are consistent with designed specifications.

The present status and the recent progress of pump-probe time-resolved photoemission electron microscopy at SPring-8 are introduced. Combining the variety of bunch operation modes available at the SPring-8 storage ring with ultra-short excitation sources including pulsed magnetic fields, electric fields and lasers, the element-specific time evolution of materials in response to the excitation can be observed with spatial and temporal resolutions of (50–300) nm and (40–100) ps, respectively, with repetition frequencies of up to 42 MHz. By using the magnetic circular dichroism effect, the domain motion of sub-micron sized magnetic areas can be observed. The time evolution of electronic structures in local areas can also be studied. The experimental setups and representative activities are described.

We have studied the electronic structure of the molecular ferromagnet β -Mn phthalocyanine ( β -MnPc) in a polycrystalline form, which has been reported to show ferromagnetism at T 8.6 K , by X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). From the experimental results and subsequent cluster-model calculation, we find that the ferromagnetic Mn ion in β -MnPc is largely in the 4 E g ground state arising from the ( e g ) 3 ( b 2 g ) 1 ( a 1 g ) 1 [ ( d x z , y z ) 3 ( d x y ) 1 ( d z 2 ) 1 ] configuration of the Mn2+ state. Considering that the highest occupied molecular orbital (HOMO) of MnPc with the 4 E g ground state originates from the a 1 g orbital of the Mn2+ ion, it is proposed that a 1 g – a 1 g exchange coupling via the π orbitals of the phthalocyanine ring plays a crucial role in the ferromagnetism of β -MnPc.