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The catalysts comprising the main active compounds of Sn-Nx were synthesized using trichlorophenylstannane ((C6H5)Cl3Sn), nitrogen carbon-dots (NCDs), and activated carbon (AC) as starting materials, and the activity and stability of catalysts was evaluated in the acetylene hydrochlorination. According to the results on the physical and chemical properties of catalysts (TEM, XRD, BET, XPS and TG), it is concluded that NCDs@AC can increase (C6H5)Cl3Sn dispersity, retard the coke deposition of (C6H5)Cl3Sn/AC and lessen the loss of (C6H5)Cl3Sn, thereby further promoting the stability of (C6H5)Cl3Sn/AC. Based on the characterization results of C2H2-TPD and HCl adsorption experiments, we proposed that the existence of Sn-Nx can effectively strengthen the reactants adsorption of catalysts. By combing the FT-IR, C2H2-TPD and Rideal-Eley mechanism, the catalytic mechanism, in which C2H2 is firstly adsorbed on (C6H5)Cl3Sn to form (C6H5)Cl3Sn-C2H2 and then reacted with HCl to produce vinyl chloride, is proposed.

In the process of treating tetracyclines in wastewater, the influence of the surrounding environment on the efficiency of tetracycline removal plays a vital role. We have successfully prepared Azo@Ag/Ag2O/CN photocatalytic materials that are intelligently responsive to light of different wavelengths via direct precipitation and emulsion polymerization. Tetracyclines are used to simulate pollutants, proving that Azo@Ag/Ag2O/CN achieves intelligent responsiveness under different wavelengths of light. Azo@Ag/Ag2O/CN exhibits conversion from a trans structure to a cis structure when irradiated by UV light, while Vis light irradiation shows the opposite reaction. The photocatalytic degradation rate of the Azo@Ag/Ag2O-10/CN photocatalyst reached 87.7% under Vis light irradiation. Azo@Ag/Ag2O/CN will be converted from a cis structure to a trans structure, and the Ag/Ag2O-10/CN photocatalyst can be released and the contact angle does not change around 130°, showing a state of relaxation. This experiment realized the controllability of the photocatalyst to light.

Fully-epitaxial magnetoresistance (MR) devices with half-metallic Heusler alloys has attracted considerable attention for years due to their excellent spin-dependent transport properties such as high MR ratio and ultra-low resistance-area product. However, their poor manufacturability due to the necessity of epitaxial growth on a special single crystalline substrate such as MgO(001) hinders their practical applications. To overcome this issue, in this study, we fabricated Heusler-based epitaxial current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) film grown on Si substrate and directly bonded it to poly-crystalline electrode wafer by using three-dimensional (3D) integration processes such as direct wafer bonding and removal of backside Si substrate. First we explored suitable seed/buffer layers for the (001)-oriented epitaxial growth of Heusler CPP-GMR on Si(001) substrate. Si-subs/NiAl/CoFe seed/buffer structure was found to induce (001)-oriented epitaxial growth and to suppress an Al diffusion from NiAl to the Heusler electrode even after annealing at 500 °C, resulting in large MR ratio comparable to that with MgO substrate. After direct wafer bonding process, the microstructure analysis revealed clean damage-free bonded interface between the epitaxial Heusler GMR and poly-crystalline electrode films with Au capping layers. After the 3D integration processes, high MR performance has been successfully reproduced. This unique processing method enables the integration of high performance Heusler-based epitaxial spintronic devices for various practical applications.

The discovery of perpendicular magnetic anisotropy (PMA) at the interface of ferromagnetic ultra-thin films and MgO has stimulated a vast interest in developing high-density magnetic random-access memory. Whilst attempts have been made to understand the origin of interfacial PMA, difficulties in distinguishing contributions from the interface and bulk layers has hampered the understanding of such phenomena. In this study, we have investigated for the first time the electronic and magnetic properties of PMA in Fe ultra-thin films on MgO in an atomic-layer resolved fashion by employing depth-resolved synchrotron Mössbauer spectroscopy to get an insight into the physical mechanism of interfacial PMA., 応用物理学会春季学術講演会2022

Large perpendicular magnetic anisotropy (PMA), high spin polarization at the Fermi level, and a low Gilbert damping constant are the crucial properties of magnetic thin films for developing high density fast switching magnetic random-access memory (MRAM). Whilst ferromagnetic materials can show high spin polarization and large PMA, they are also sensitive to stray fields which can influence their performance in spintronic devices. Ferrimagnetic materials, specifically those which demonstrate a partially to fully compensated magnetic moment, are not only insensitive to stray field effects but also possess extremely low Gilbert damping constants around the compensation temperature. The first demonstration of a fully compensated ferrimagnetic material was in the full-Heusler Mn2RuGa (MRG) compound. However, MRG thin films suffer from problems such as thickness dependency and relatively low spin polarization, and therefore there has been a push to explore a wider range of Mn2YZ Heusler alloys to find the optimal ferrimagnetic material for MRAM applications, 応用物理学会春季学術講演会2022

Soft magnetic FeCoAlO thin films were prepared by asymmetric targets, and their magnetic properties and high-frequency characteristics were studied. The coercivity Hc of the films initially decreased with increasing the number of Al2O3 chips on the Fe70Co30 target. Then, the minimum value of the coercivity was observed for the film prepared with 12 Al2O3 chips (Hc||= 6.3 Oe and Hc⊥ = 1.9 Oe, Hk = 110 Oe), and as more Al2O3 chips were added, the coercivity increased. The good soft magnetic properties of the films mainly came from the refinement of grain size. The films also had excellent high-frequency response, i.e., fr = 3.4 GHz, and the real part of the permeability μ′ at low frequency had a large value of approximately 200 for the film prepared with 12 Al2O3 chips. For 16 Al2O3 chips, the film had fr = 3.7 GHz and μ′ ~ 150 when f

Fully-epitaxial magnetoresistance (MR) devices with half-metallic Heusler alloys has attracted considerable attention for years due to their excellent spin-dependent transport properties such as high MR ratio and ultra-low resistance-area product. However, their poor manufacturability due to the necessity of epitaxial growth on a special single crystalline substrate such as MgO(001) hinders their practical applications. To overcome this issue, in this study, we fabricated Heusler-based epitaxial current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) film grown on Si substrate and directly bonded it to poly-crystalline electrode wafer by using three-dimensional (3D) integration processes such as direct wafer bonding and removal of backside Si substrate. First we explored suitable seed/buffer layers for the (001)-oriented epitaxial growth of Heusler CPP-GMR on Si(001) substrate. Si-subs/NiAl/CoFe seed/buffer structure was found to induce (001)-oriented epitaxial growth and to suppress an Al diffusion from NiAl to the Heusler electrode even after annealing at 500 °C, resulting in large MR ratio comparable to that with MgO substrate. After direct wafer bonding process, the microstructure analysis revealed clean damage-free bonded interface between the epitaxial Heusler GMR and poly-crystalline electrode films with Au capping layers. After the 3D integration processes, high MR performance has been successfully reproduced. This unique processing method enables the integration of high performance Heusler-based epitaxial spintronic devices for various practical applications.

Loading of ZnFe2O4 on ultrathin MoS2 nanosheets were performed to enhance the photocatalytic activity and recovery property by a facile hydrothermal method. The ZnFe2O4/MoS2 photocatalysts showed a relatively high photocatalytic activity than ZnFe2O4 and MoS2 under visible light irradiation, and the degradation rate of tetracycline hydrochloride by the MoS2/ZnFe2O4-25% photocatalysts is up to 95%. Systematical characterization demonstrated that the synergistic effect of nanosheets structure of MoS2 and heterostructures formed by ZnFe2O4 and MoS2 could effectively enhance light absorption ability, increase reactive sites, inhibit recombination of the photo-generated electrons and holes, accelerate the photo-generated electrons transfer speed, and improve photocatalytic performance of the photocatalysts. The ZnFe2O4/MoS2 photocatalysts could be recovered quickly under the external magnetic field and reused four times with no significant decrease in photocatalytic activity. The ·O2− is the main active species.

The photocatalytic reclamation of the environment requires improved catalysts, as severe charge recombination currently limits their practical application. This study describes a simple synthesis of SnO2−x/Sb2O3 composite by the mechanical milling method. The coupling of SnO2−x possessing oxygen vacancies (OVs) with Sb2O3 is a new approach for obtaining materials with outstanding photocatalytic properties. For the photo-oxidation of isopropanol (IPA) within 5 h, the acetone yield over SnO2−x/Sb2O3 composite with mass ratio of 1:4 was 22.67 and 10.5 times higher than those of SnO2−x and Sb2O3, respectively, and the carbon dioxide output was 13.29 and 7.46 times higher than those of SnO2−x and Sb2O3, respectively. This results showed that the OVs-induced SnO2−x/Sb2O3 heterostructures have a very high IPA photo-oxidation catalytic degradation activity, even after six cycles with no obvious decline. Combination of defect engineering and heterojunction can be a powerful tool for obtaining broad light absorption and high photo-induced charge separation efficiency, which contributes to improving the photocatalytic IPA degradation property.

NixZn1−xFe2O4/CNTs composite photocatalysts were prepared via a facile hydrothermal method, and their physical and chemical properties were investigated. The effect of different Ni doping amounts on the photocatalytic activity of NixZn1−xFe2O4 and Ni0.5Zn0.5Fe2O4/CNTs photocatalysts containing different amounts of carbon nanotubes (CNTs) were investigated for their ability to degrade tetracycline (TC) in wastewater. The results showed that Ni0.5Zn0.5Fe2O4/CNTs (5% CNTs) had the highest photocatalytic activity, achieving a TC degradation of 96%. The origin of the excellent performance of the photocatalysts, as well as the photodegradation mechanism, were also discussed. Effective electron–hole separation is believed to be responsible for the significantly improved photocatalytic activity. After four photocatalytic degradation experiments, the composite photocatalyst retained its high photocatalytic activity, and the results showed that the composite photocatalysts were highly stable and could be magnetically separated.

Ag dots/flower-like MoS2/rGO multidimensional photocatalysts were successfully prepared via one-pot hydrothermal method. The characterizations of morphology and structure showed that the as-prepared photocatalysts with zero dimensional Ag dots, three dimensional flower-like MoS2 and two dimensional rGO composite structures have been clearly formed in composite multidimensional photocatalysts. Moreover, the photoelectronic performances exhibited that the composite multidimensional structure could efficiently enhance the transfer rate of charges. Especially the intensity of photocurrent was obviously improved after the Ag dots modified MoS2/rGO. The Ag/MoS2/rGO showed excellent photocatalytic activity of degradation tetracycline (TC), the removed rate of TC could reach 85.5% in 90 min. The species trapping experiments and electron spin resonance spin-trap tests clearly revealed that the h+ and ·O2− active species play the key roles during the photocatalytic degradation processes of TC. Overall, the composite multidimensional photocatalysts with zero, three and two dimensional in this work show a promising way to remove the TC wastewater, which suggested one strategy fabricate high active photocatalyst, and the photocatalytic mechanism was also discussed.

A new type of pure organic 5,10,15,20-tetra (4-hydroxyphenyl) porphyrin (TPPH)/[Formula: see text]-C3N4 nanohybrid was prepared to expand the light absorption range of graphitic carbon nitride materials. The morphology and structure of the composites were systematically characterized by scanning electron microscope, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Results show that after the introduction of TPPH, the visible light area optical absorption of the composite sample increased significantly under the noncovalent interaction of TPPH and [Formula: see text]-C3N4, and the electrochemical impedance spectroscopy and [Formula: see text]–[Formula: see text] measurements confirmed the improved charge separation efficiency of the sample and showed excellent photocatalytic hydrogen production capacity. Under full spectrum irradiation, the hydrogen production of 1.67% TPPH/[Formula: see text]-C3N4 without adding co-catalyst reached 10.87[Formula: see text]mmol[Formula: see text][Formula: see text], about 2.68 times that of pure [Formula: see text]-C3N4 (4.06[Formula: see text]mmol[Formula: see text][Formula: see text]), which showed effective promotion of the electron transfer between TPPH and [Formula: see text]-C3N4.

Negative-spin-polarization material generates a spin current whose spin direction is opposite to the magnetization direction. This characteristicis technologically important because it can increase the freedom in the designof spintronic devices. In this paper, westudied FeCr from the viewpoints of the band structure, atomic magnetic moments, and local atomic arrangementto explore the potentiality as a negative-spin-polarization material. Thefirst-principlescalculation on the disordered FeCr alloypredicted a high negative spin polarization, whichis attributed to the band matching of the minority spin.We experimentally fabricated Fe1-xCrxthin film in the Cr-concentration (x) range from 0.2 to 0.4 by sputter deposition. The spin polarization of Fe0.7Cr0.3 estimated from current-perpendicular-to-plane giant magnetoresistance was −0.28 and fell below the calculated value. The synchrotron X-ray magnetic circular dichroism (XMCD)measurement showed the ferrimagnetic configuration of the magnetic moments of Fe and Cr. The Fe moment shows a large moment over the wide Cr concentration range, whereas the Cr moment decreased with the Cr concentration, which agrees with the calculation result. The synchrotron Mössbauer spectroscopy measurement indicated the inhomogeneity of the FeCr composition even in the as-deposited state. It was also found that Fe-rich region was formed after annealing, reflecting the phase separation nature of the FeCr system.The inhomogeneity was not considered in the calculation and could be the origin of the low spin polarization observed in the experiment.

One-through process of graphene growth on insulator substrates with inserting a hexagonal boron nitride (h-BN) buffer layer is expected to yield significant improvements in performance of electron transport properties of graphene devices due to the alleviation of the interface interaction between graphene and insulators and the enhancement of the flatness of the substrate. In this study, we successfully fabricated a graphene/h-BN/SiO2 heterostructure by direct chemical vapor deposition (CVD) without mechanical transfer processes. It was found that h-BN promotes the growth of graphene on SiO2 whereas the graphene growth without the h-BN layer is extremely difficult. The electronic structures of graphene and h-BN were investigated by using micro-Raman spectroscopy and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The B and N K-edge NEXAFS revealed that substitutional oxygen impurities with the chemical form of BN3−xOx (x = 1, 2, 3) are present in both h-BN/SiO2 and graphene/h-BN/SiO2. The number of O substitutional impurities is two times larger in graphene/h-BN/SiO2 than in h-BN/SiO2, which is presumed to be due to the reaction with oxygen from SiO2 and methanol during the graphene growth. The interfacial interaction between graphene and h-BN was found to be weak in graphene/h-BN/SiO2. The present study shows that the h-BN layer grown with CVD can be a superior buffer layer for graphene devices which enables direct graphene growth on it and to decrease the interactions with insulator substrates.

The glutathione (GSH) and mercaptopropionic acid (MPA) modified internal defect-rich, surface defects-poor near infrared (NIR) Zn–CuInSe2 (ZCISe) QDs were synthesized. Nanoporous ZnO nanosheets (NS) were firstly loaded with those ZCISe QDs to improve photoelectrochemical response in the NIR light region. Then loading Mn doping CdS thin film onto the ZCISe/ZnO NS was further used to reduce the interfacial recombination between different components of hybrid photoelectrode, in addition to enhance the light absorption and resist the photo-oxidation decomposition of the photocatalysts. Successively introducing ZCISe and Mn–CdS onto ZnO NS can increase the photocurrent intensities from 1 mA/cm2 for naked ZnO NS, 2.2 mA/cm2 for ZCISe/ZnO NS, to 9 mA/cm2 for Mn–CdS/ZCISe/ZnO NS. Here, excellent performance of ZCISe based ZnO NS photoelectrode is mainly attributed to an intrinsic defect state-related donor–acceptor pair (DAP) in ZCISe QDs with long-lived photogenerated carriers. Photocatalytic properties of Mn–CdS/ZCISe/ZnO NS were evaluated by removing azo dyes with an efficiency of 83%, an enhancement of 97% compared to that of ZnO NS.

A novel magnetic double-conductive photocatalyst of Fe3O4@Bi2O3/C was successfully prepared by microwave and deposition technology, and it showed satisfactory photocatalytic activity in the degradation of tetracycline compared with that of pure Bi2O3 under visible light. The improved degradation efficiency of the as-prepared Fe3O4@Bi2O3/C is attributed to the better conductivity of biomass carbon and Fe3O4 quantum dot, which significantly inhibited the recombination of electron–hole pairs and improved the optical absorption. In addition, the mechanism exploration of the radical trapping experiments and ESR measurement indicated that h+, ˙O2− and ˙OH participated in the tetracycline removal procedure. The possible photocatalytic reaction mechanisms including transfer behavior of charge carriers and the intermediate products of tetracycline degradation were also revealed in depth. This work provides a promising approach to construct a biomass carbon-based photocatalyst for the wastewater treatment.

A novel polyaniline (PANI)/Sn3O4 heterojunction composed of PANI nanofibers and Sn3O4 nanosheets was fabricated by a facile physical milling technique. Modification of Sn3O4 with a PANI conductive polymer contributes to facilitating interfacial charge transfer efficiency, and thus, significantly enhances the visible-light Rhodamine B (RhB) photo-degradation. Results indicate that PANI/Sn3O4 heterostructures with 10 wt% PANI reached the maximum degradation efficiency (around 97%) for RhB within 5 h, which is 2.27 times higher than that of Sn3O4 alone. This improvement is due to the p–n heterostructure formation in PANI/Sn3O4. Moreover, the outcome of reactive species capturing experiments demonstrated that in PANI/Sn3O4, holes made the largest contribution to RhB degradation under visible light illumination, while hydroxyl radicals showed less significance under the same conditions. In addition, the photocatalytic mechanism was proposed based on evidence from the reactive species test and energy band structure analysis.

The origin of the interfacial perpendicular magnetic anisotropy (PMA) induced in the ultrathin Fe layer on the Au(111) surface was examined using synchrotron-radiation-based M\"ossbauer spectroscopy (MS), x-ray magnetic circular dichroism (XMCD), and angle-resolved photoemission spectroscopy (ARPES). To probe the detailed interfacial electronic structure of orbital hybridization between the Fe $3d$ and Au $6p$ bands, we detected the interfacial proximity effect, which modulates the valence-band electronic structure of Fe, resulting in PMA. MS and XMCD measurements were used to detect the interfacial magnetic structure and anisotropy in orbital magnetic moments, respectively. In situ ARPES also confirms the initial growth of Fe on large spin-orbit coupled surface Shockley states under Au(111) modulated electronic states in the vicinity of the Fermi level. This suggests that PMA in the Fe/Au(111) interface originates from the cooperation effects among the spin, orbital magnetic moments in Fe, and large spin-orbit coupling in Au. These findings pave the way to develop interfacial PMA using $p\text{\ensuremath{-}}d$ hybridization with a large spin-orbit interaction.

「夢の素材」と呼ばれるグラフェンは、厚さが究極的に薄くしなやかで強く、ユニークな物理、光学、電気的性質を持つため、様々な分野で応用に関する研究開発を進められています。その中で、スピンの散乱が生じにくいことや電子を高速かつ低抵抗で流すことができることなどスピンの輸送に適した性質から、グラフェンはスピントランジスタや超高記録密度磁気メモリなど次世代の省エネ・高集積化スピントロニクスデバイスへの応用に有望なスピントロニクス材料として注目されています[1, 2]。しかし、これまでに研究されたグラフェンを用いたスピントロニクスデバイスでは、上記の性質から期待されるような高い性能は実現されておらず、応用に向けた道筋は見えていません。このような低い性能の原因として、従来のグラフェンスピントロニクスデバイスでは、デバイスの中でグラフェンと積層して用いられる磁性体の材質がスピン偏極率が低い一般的な磁性材料(ニッケルやコバルト等)に限られてきたことが考えられます。このような状況の下、我々はハーフメタルと呼ばれ100%のスピン偏極率を持つ磁性材料であるホイスラー合金に着目し、グラフェンとホイスラー合金を積層する技術の開発に取り組み、厚さが一原子層のグラフェンがホイスラー合金の表面を完全に被覆したグラフェン/ホイスラー合金ヘテロ構造（右図）の作製に成功しました [3]。さらに、グラフェン/ホイスラー合金ヘテロ構造の界面の電子・磁気的状態をXMCDおよびTRHEPD分光により調べた結果、グラフェンとホイスラー合金が接する界面においても、ホイスラー合金が本来持っている磁性や高いスピン偏極率が失われていないことや、ディラックコーンと呼ばれるグラフェンのスピン輸送を担う電子状態が保たれていることが分かりました。これらの結果から、今後、グラフェン/ホイスラー合金ヘテロ構造を用いることで、グラフェンスピントロニクスデバイスの飛躍的な高性能化の実現が期待できます。, 低速陽電子実験施設研究会

「夢の素材」と呼ばれるグラフェンは、その卓越したスピン伝導性から次世代スピントロニクス材料として注目されている[1,2]。しかし、現在のグラフェンスピントロニクス素子は、金属スピントロニクス素子と比較して性能が低く、特性向上が大きな課題になっている。グラフェンスピントロニクス素子の性能が低い原因の一つとして、従来の素子では、スピン偏極率が低い一般的な磁性材料(Co, Ni, Fe等)が使われてきたことが考えられる。我々は、一般的な磁性材料の代わりに、高スピン偏極率なハーフメタルホイスラー合金を用いることによるグラフェンスピントロニクス素子の高性能化の研究に取り組んでいる。本研究では、ホイスラー合金・グラフェンスピントロニクス素子の実現の鍵となる、グラフェンとホイスラー合金からなる積層材料の創製に成功した[3]。さらに、放射光分光を用いて積層材料の界面物性の調査を行った。, QST高崎サイエンスフェスタ2020

The energy spectrum of positronium atoms generated at a solid surface reflects the electron density of states (DOS) associated solely with the first surface layer. Using spin-polarized positrons, the spin-dependent surface DOS can be studied. For this purpose, we have developed a spin-polarized positronium time-of-flight spectroscopy apparatus based on a $^{22}\mathrm{Na}$ positron source and an electrostatic beam transportation system, which enables the sampling of topmost surface electrons around the $\mathrm{\ensuremath{\Gamma}}$ point and near the Fermi level. We applied this technique to nonmagnetic Pt(111) and W(001), ferromagnetic Ni(111), Co(0001) and graphene on them, ${\mathrm{Co}}_{2}{\mathrm{FeGa}}_{0.5}{\mathrm{Ge}}_{0.5}$ (CFGG) and ${\mathrm{Co}}_{2}\mathrm{MnSi}$ (CMS). The results showed that the electrons of Ni(111) and Co(0001) surfaces have characteristic negative spin polarizations, while these spin polarizations vanished upon graphene deposition, suggesting that the spin polarizations of graphene on Ni(111) and Co(0001) were mainly induced at the Dirac points that were out of range in the present measurement. The CFGG and CMS surfaces also exhibited only weak spin polarizations suggesting that the half-metallicity expected for these bulk states was not maintained at the surfaces.

Graphene/ferromagnet heterostructures are receiving an intensive interest due to the expectation of both improving the existing storage devices and paving the way for the next generation of memory technologies with higher speed and lower power consumption. The long spin diffusion length in graphene originated from the weak spin-orbit interaction and high electron mobility has stimulated numerous studies on developing graphene-based lateral spin valves (SV) in the past decade [1]. Apart from the application to lateral SV dealing with in-plane spin transportation in a graphene channel, another potential application that is the implementation of graphene as a spacer material in vertical SV has recently become a subject of intense interest [2]. Up to now, the ferromagnets involved in the graphene/ferromagnet heterostructures are limited to the conventional magnetic materials with low spin-polarization, which corresponds for the poor performance found in those graphene/ferromagnet heterostructures based spintronic devices. In order to improve the performance of graphene/ferromagnet based spintronic devices, we recently developed a novel heterostructure which consists of a single layer graphene (SLG) on a full Heusler alloy CoFeGe0.5Ga0.5 (CFGG) ferromagnet with high-polarization [3], by in-situ chemical vapor deposition and magnetron-sputtering technique. The growth of high-quality with a full coverage of SLG on CFGG was succeeded by careful optimization of the growth procedure. The spin-resolved electronic properties of the interface region in the SLG/CFGG heterostructure were examined by depth-resolved x-ray magnetic circular dichroism spectroscopy with atomic depth resolution. It is revealed that the SLG/CFGG heterostructure shows not only a quasi-free-standing nature of SLG but also a robust magnetism comparable to that of bulk one in the atomic layer adjacent to SLG. In addition, the density functional theory calculation results indicate the linear Dirac band structure of graphene and half-metallicity of CFGG in the vicinity of the interface are well preserved in the SLG/CFGG heterostructure. The unusual preservation of the inherent electronic and magnetic properties at the SLG/CFGG interface is associated with the weak van der Waals interactions at the interface, which differs from other reported graphene/ferromagnet heterostructures where a strong interfacial interaction of chemical bonding was usually observed. The possibility of using this newly developed SLG/CFGG heterostructure for realizing high-performance graphene spintronic devices will be also discussed., 4th QST international symposium

Modifying TiO2 with noble metal nanocrystals via photodeposition is an efficient strategy for improving its photoelectrochemical performance. The photodeposition process is still an open question and needs to be further clarified. Herein, we selectively deposited Pb or Cu on Au nanocrystals supported by the branched TiO2 nanostructure to prepare the Au@metal/semiconductor photocatalyst. The results revealed the dependence of the photodeposition mechanism on the type of electrolyte. In an acetic acid–acetate system Pb deposition on Au undergoes both underpotential and overpotential deposition processes, while Cu deposition on Au only displays overpotential deposition behavior. In a nitric acid–nitrate system, however, only underpotential deposition occurs during Pb deposition on Au. Surface microstructure analysis shows that the Cu–Au bimetallic nanocrystals form a typical core/shell structure, while Pb–Au has a Janus structure. The lower ideality factor of Cu/Au–TiO2 than that of Pb/Au–TiO2 indicates an ideal photoelectrode/electrolyte junction for photoelectrochemical reaction, further enhancing carrier transport with a short recombination lifetime of 0.899 ms. Finally, the evaluation of photoelectrochemical performance further confirmed Cu/Au–TiO2 (Au loading amount of about 0.55 mass%) as the optimal photocatalyst, with an efficiency as high as 0.29% or about 1.93 times that of Au–TiO2 (0.15%).

The relationship between the magnetization and magnetic moment at each Fe site in Sm(Fe 1− x Co x ) 12 compounds and their temperature dependence were investigated via synchrotron Mössbauer spectroscopy. The enhancement in the Fe magnetic moments in the Sm(Fe 1− x Co x ) 12 compounds with increasing Co content was observed at a similar rate as the increment in their saturation magnetization at 300 K. We found that the magnitudes of the Fe magnetic moments vary in a descending order: 8i > 8j > 8f, and they are independent of the Co content because the variation is caused by the magneto-volume effect. The curvatures of the temperature dependence of the Fe-sublattice magnetic moments are larger and also vary in the order of 8i > 8j > 8f because the enhancements in the exchange couplingstrength decrease in the same order.

Perpendicular magnetic anisotropy (PMA) is induced at the Fe/Au(111) interface. We examine the origin of PMA using synchrotron radiation Mossbauer and photoemission spectroscopies. From the spectral analysis, we detected the interfacial proximity effect which modulates the valence-band electronic structure by depositing Fe. Further, we explain that these spectroscopies are also powerful techniques to investigate the interfacial electronic and magnetic properties., 第81回日本応用物理学会秋季学術講演会

Two-dimensional materials such as hexagonal boron nitride (h-BN) and graphene have attracted wide attention in nanoelectronics and spintronics. Since their electronic characteristics are strongly affected by the local atomic structure, the heteroatom doping could allow us to tailor the electronic and physical properties of two-dimensional materials. In this study, a non-chemical method of heteroatom doping into h-BN under high-energy ion irradiation was demonstrated for the LiF/h-BN/Cu heterostructure. Spectroscopic analysis of chemical states on the relevant atoms revealed that 6% ± 2% fluorinated h-BN is obtained by the irradiation of 2.4 MeV Cu2+ ions with the fluence up to 1014 ions cm-2. It was shown that the high-energy ion irradiation leads to a single-sided fluorination of h-BN by the formation of the fluorinated sp 3-hybridized BN.

For years graphene has been considered as the most potential material which paves the way to advanced high-performance spintronic devices due to its extraordinary electrical and physical properties. The long spin diffusion length in graphene originated from the weak spin-orbit interaction and high electron mobility has stimulated numerous studies on developing graphene-based lateral spin valves (SV) in the past decade [1]. Apart from the application to lateral SV dealing with in-plane spin transportation in a graphene channel, another potential application that is the implementation of graphene as a spacer material in vertical SV has become a subject of intense interest in recent years [2]. In those reported graphene-spintronic devices, conventional ferromagnets such as NiFe and Co etc. of low spin polarization have been used due to the well-established synthesis method of graphene on them. However, the low spin signal and tiny magnetoresistance effect reported in those systems make graphene still far from being considered satisfactory for spintronic device applications. Adopting highly spin-polarized material such as half-metals can be the most effective way to improve the performance of graphene spintronic devices, the experimental demonstration, however, is still lacking. Here, we report the demonstration of the in-situ fabrication of a novel heterostructure consisting of graphene and full Heusler alloy Co2Fe(Ge0.5Ga0.5) (CFGG), in which half-metallicity has been confirmed experimentally [3]. Single layer graphene was prepared by in situ chemical vapor deposition on a magnetron sputtered epitaxial CFGG thin film grown on single crystalline MgO(001) substrate. As shown by the RHEED images in Fig. 1, the sharp streaky patterns from both graphene and CFGG indicate an atomic flatness of the SLG/CFGG interface. The high quality of graphene was further confirmed by Raman spectroscopy. A depth-resolved XMCD study reveals that the CFGG surface adjacent to SLG possesses a robust magnetic moment comparable to the bulk CFGG (Fig. 2) in association with the weak interfacial interaction between graphene on CFGG. This finding is in sharp contrast to the large reduction of the magnetic moment reported in other graphene/ferromagnets heterostructures. DFT calculations show that, the inherent properties such as half-metallicity of CFGG and the linear Dirac band of graphene are preserved at the interface. These findings are highly promising for realizing effective transport of highly spin-polarized electrons in graphene-based spintronic devices [1]W. Han et al, Nat. Nanotechnol. 9, 794 (2014) [2] E. D. Cobas, et al, ACS Nano 10, 10357 (2016) [3] S. Li et al, Appl. Phys. Lett. 103, 042405 (2013), 63th international conference on Magnetism and Magnetic Materials (MMM) 2019に出席するため

Firstly, B, Ni co-doped TiO2 (B–Ni–TiO2) was prepared by sol–gel method, g-C3N4 was prepared by calcination method. Secondly, B–Ni–TiO2/g-C3N4 composite photocatalysts were prepared by heating reflux method. The physical and chemical properties of the composite photocatalysts were characterized by XRD, XPS, UV–Vis, FT-TR, SEM, PL and TEM, HRTEM. The effect of different photocatalysts on the degradation of chloramphenicol was investigated. After the combination of g-C3N4 and B–Ni–TiO2, the separation efficiency of photo-generated electrons and holes can be accelerated and the photocatalytic activity can be improved. When the ratio of g-C3N4 and B–Ni–TiO2 was 1:4, the degradation rate of chloramphenicol by the composite photocatalyst was up to 95%. After five photocatalytic degradation experiments, the photocatalytic activity of the composite photocatalyst was not significantly reduced, the result showed that the composite photocatalyst had better stability and regeneration performance. The ·O2− was responsible for the photodegradation activity were determined and a possible mechanism was proposed.

Ternary shell/core/core Bi2S3/graphene quantum dots/TiO2 nanowire arrays (Bi2S3/GQDs/TNWs) photoelectrodes are constructed through electrophoretic deposition of GQDs onto TNWs followed by electrochemical deposition of Bi2S3 QDs. An interesting synergistic effect was observed in configuration of Bi2S3/GQDs/TNWs. Under irradiation, the photocurrent density of 50 μA/cm2 (an enhancement of ∼86%) and the removal efficiency of Cr (VI) is 97% (an enhancement of ∼76%) compared to that TiO2 nanowire array were obtained. Such significant enhancement is attributed to the strong photoabsorption ability of Bi2S3 QDs and excellent electron transport ability of GQDs.

The near-future ultra-high-density magnetic recording with an assist recording technology requires a substantial evolution of the read-head technology. A read sensor with a small sensor resistance-area product ( $RA$ ), a large magnetoresistance ratio ( $\Delta R/R$ ), and a thin total sensor thickness is required for the low bit error rate and high-spatial resolution of reading. We developed current-perpendicular-to-plane giant magnetoresistance sensors using highly spin-polarized Heusler alloy ferromagnetic layers with the spin polarization of the conducting electron $\beta \sim 0.8$ . A reasonably large $\Delta R/R$ up to 14% was obtained by a practical bottom-pinned spin-valve structure with a conventional metallic spacer layer of an Ag90Sn10 (AgSn) alloy. By replacing the spacer layer with a conductive oxide-based AgSn/InZnO bilayer, a large $\Delta R/R$ up to 32% was realized at RA value of $\sim 0.1~\Omega \cdot \mu \text{m}^{{\mathbf {2}}}$ , which is optimal for the read sensor application. A large voltage output up to 6 mV was obtained for a sensor utilization of ~33% at a bias voltage of 100 mV.

We studied the origin of the enhancement of current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) effect by inserting a thin amorphous CoFeBTa (CFBT) underlayer below a Co2(Mn0.6Fe0.4)Ge (CMFG) Heusler alloy ferromagnetic (FM) layer. Large magnetoresistance ratio of ∼25% and resistance change-area product of ∼7.5 mΩ μm2 were obtained at room temperature by inserting a CFBT (1.2 nm) underlayer. X-ray diffraction (XRD) and transmission electron microscope analyses confirmed that the CMFG FM layer deposited on the CFBT underlayer was amorphous in the as-deposited state and crystallized to a B2-ordered polycrystalline film by annealing at 300 °C. The degree of B2 order (SB2) of the CMFG films was estimated by anomalous XRD using x-ray energies around the Co K-absorption edge. SB2 of the CMFG film deposited on the amorphous CFBT (1.2 nm) underlayer was ∼0.76, much larger than that of the CMFG film deposited on a crystalline CoFe underlayer (SB2 ∼0.47). First-principles calculations indicated that the spin polarization of the sp-conduction electrons in CMFG increases with increasing SB2, which accounts for the enhanced CPP-GMR effect in the pseudo spin-valve by inserting an amorphous CFBT underlayer.

We report the Mössbauer spectra using circularly-polarized synchrotron-radiation beams for the Fe/Au interface. For the interfacial studies in Multilayers, the doping of 57 Fe into the thin Fe layer enables to probe of the interfacial electronic and magnetic structures. Here, the Mössbauer spectroscopy using linearly or circularly polarized synchrotron-radiation beam for Fe/Au interface clarifies the local environments around the Fe atoms, which is compared with the case of perpendicularly magnetic anisotropy (PMA) presented by the previous report [J. Okabayashi et al., Phys. Rev. B 103, 104435 (2021)]. Contrary to the PMA case, the hyperfine fields are consistent with a model that defines the diffusive bulk-like Fe atoms without the interfacial components.

Surface magnetism of Fe (001) was investigated by the in situ iron-57 probe layer method with a synchrotron Mössbauer source. The observed layer-by-layer internal hyperfine field shows a marked reduction at the surface and an oscillatory behavior with increasing depth in the individual layers below the surface. The calculated layer-by-layer hyperfine interactions (hyperfine field, isomer shift, and quadrupole shift) were consistent with the experimental results. The results give direct evidence for the magnetic Friedel oscillations, penetrating several layers from the Fe (001) surface.

A novel heterostructure consisting of single-layer graphene (SLG) and half-metallic Co2Fe(Ge0.5Ga0.5) (CFGG) Heusler alloy ferromagnet were synthesized, and the electronic properties of the interface were examined by depth-resolved X-ray magnetic circular dichroism spectroscopy. We found that in the SLG/CFGG heterostructure the SLG has a quasi-free-standing nature and the CFGG preserves the half-metallic ferromagnetism in the vicinity of the interface, which suggested that the SLG/CFGG heterostructure possesses distinctive advantages over other reported graphene/ferromagnet heterostructures for realizing high-performance spintronics devices.

The energy spectrum of positronium atoms generated at_solid surface reflects the electron density of states (DOS) associated solely with the first surface layer.Using spin-polarized positrons, the spindependent surface DOS can be studied.For this purpose, we have developed_spin-polarized positronium time-of-flight spectroscopy apparatus based on_22 Na positron source and an electrostatic beam transportation system, which enables the sampling of topmost surface electrons around the Γ point and near the Fermi level.We applied this technique to nonmagnetic Pt(111) and W(001), ferromagnetic Ni (111), Co(0001) and graphene on them, Co2FeGa0 .5Ge0 .5 (CFGG) and Co2MnSi (CMS).The results showed that the electrons of Ni(111) and Co(0001) surfaces have characteristic negative spin polarizations, while these spin polarizations vanished upon graphene deposition, suggesting that the spin polarizations of graphene on Ni(111) and Co(0001) were mainly induced at the Dirac points that were out of range in the present measurement.The CFGG and CMS surfaces also exhibited only weak spin polarizations suggesting that the half-metallicity expected for these bulk states was not maintained at the surfaces.

Magnetic properties and high frequency characteristics of (Fe70.6Co29.4)100−xZrx (x = 4.0 − 18.2 at.%) thin films have been investigated. The saturation magnetization 4πM s decreases continuously from 21.7 kGs for x = 4.0 at.% to 12.2 kGs for x = 18.2 at.% and it is consistent with the decreasing of Fe-Co composition. It is found that the films show nearly isotropic magnetic behavior in the film plane for the Zr content ranging from 7.2 to 18.2 at.%. These films exhibit a weak perpendicular magnetic anisotropy with coercivity values of 24–67 Oe. Meanwhile, the in-plane isotropic FeCoZr films show a good high frequency response of permeability. In particular, the film with x = 7.2 at.% shows a resonance frequency of 2.8 GHz along the direction perpendicular to the stripe domain axis. The permeability spectra of the thin films with higher Zr content display multiple resonance peaks, which may be due to the perpendicular magnetic anisotropy induced by the stress.

A novel polyaniline (PANI)/Sn