Katsuaki Sato

Tokyo University of Agriculture and Technology | TUAT · Department of Applied Physics

MnP and Mn2P nanowhiskers have been grown by molecular-beam epitaxy (MBE) technique on InP(100) and GaAs(111)B substrates. The catalyst-free growth of nanowhiskers is found to be depended on the formation of Mn-based nanoclusters. The magnetic properties of the samples have been investigated by the measurements in a vibrating sample magnetometer.

Photoluminescence of CdGeP2 (112) single crystal and CdGeP2 epitaxial film grown on GaAs (001) substrate have been studied and their spectral similarity found. Spectral bands associated with donor/acceptor transitions peak at close energies for both substances and all are lower than the energy gap of the chalcopyrite crystal.On the other hand, the...

Ternary MnGeP2 thin films have been grown on GaAs substrate using MBE technique. The films prepared at 435 °C showed ferromagnetism at room temperature. TEM observation revealed a segregation of MnP tile-shaped grains. Films grown at 585 °C showed no trace of ferromagnetic secondary phases in XRD profiles and were found to show no ferromagnetic beh...

A giant narrowing of the energy gap in the nonlinear optical crystal ZnGeP2 (ZGP) after the incorporation of manganese atoms into the chalcopyrite crystal lattice has been detected. The (Zn,Mn)GeP2 (ZMGP) thin films grown by solid-phase endotaxy on ZGP (001) substrate share the tetrahedrally coordinated structure of chalcopyrite. The measured fine...

This paper provides a comprehensive review of magneto-optical (MO) spectroscopy. In the first place, different methods of MO measurements such as the Faraday effect, MO Kerr effect, and Cotton-Mouton effect are briefly introduced. Next, macroscopic and microscopic origin in magnetic materials is summarized. In the third part, measuring techniques f...

The strategic proposal (2019FY) “Future Materials Exploring Initiative-Engineering for Diverse Stable Phases“ compiled by JST/CRDS is briefly summarized.

Introductory talk on Magnetism for Young Researchers of Spintronics

Compound semiconductor-based solar cells 1. What kind of materials are used in solar cells for space application? 2. What is the CIGS solar cells? 3. How to fabricate solar panels of CIGS? 4. How to avoid the use of rare metals? 5. What is perovskite type organic/inorganic solar cells?

This book is planned to give comprehensive insight into spintronics with a particular reference to materials and processes for next generation innovative devices.

Among the numerous magnetic measurement techniques, I pay particular attentions to the Gauss meter for magnetic flux density, the magnetometer for magnetization, and the magnetic torque meter for magnetic anisotropy measurements.

Spectroscopy is one of the most prevalent characterization techniques for the materials sciences, since it is performed in a contact-free and non-destructive manner. Tips for absorption spectroscopy using conventional double-beam spectrophotometer are introduced first, as well as tips for photoluminescence spectroscopy using ad-hoc setups employing...

A new semiconductor material, which comprises a solid solution of a ternary diamond-like semiconductor and transitional element Mn, was grown and studied. According to X-ray diffraction data, the crystal structure of the material is similar to that of the CdGeP2 host substance with a chalcopyrite-type crystal structure. The interplanar distances an...

Present status and Problem of MO-SNOM (Seminar Text for Applied Magnetics) in Japanese History of development of scanning near-field magneto-optical microscope (MO-SNOM) is briefly reviewed and application of the MO-SNOM to observation of recorded marks on MO disk is described in detail.(In Japanese)

Highly L10-ordered FePt thin films with a strong (001) texture were successfully fabricated on amorphous substrates simply by co-sputtering and rapid thermal annealing at a low temperature of 400 °C. The morphology of FePt thin films depended strongly on the heating rate, changing from a continuous structure with an atomically flat surface to an is...

As preface of the special issue of Spintronics, brief introduction to recent developments of the field.

Ternary diamond-like compounds in II–IV–V2 semiconductor system heavily-doped with transition d-element Mn have been recently prepared. The materials grown in both forms — single crystal layers and polycrystalline bulks — exhibit well defined ferromagnetic hysteresis with a saturation behavior in the magnetization curve up to above room temperature...

Remote control of aptamer function has allowed us to control protein function in space and time. Here, we propose a novel control system for aptamer function by radiofrequency magnetic field- (RFMF-) induced local heating of a gold nanoparticle conjugated with an aptamer. In this study, we used a 31-mer thrombin-binding aptamer (TBA), which can inh...

Resonant X-ray emission spectroscopy (RXES) experiments were carried out in a single crystal of chalcopyrite CuFeS2, an antiferromagnetic semiconductor with a golden lustre, to unravel the overlapping d–d and charge-transfer transitions extending well above the absorption edge, which cannot be observed by conventional optical absorption experiments...

MnP nanowires have been grown by molecular beam epitaxy (MBE) without any preliminary deposited metal catalyst on InP(100) and GaAs(111)B substrates. Mn was supplied using a conventional Knudsen cell, whereas P2 was supplied as a gas by the decomposition of tertiary butylphosphine (TBP) using a cracking cell. The self-assembled growth of nanowires...

MgB2 films grown by molecular beam epitaxy method were investigated by means of magneto-optical (MO) method. Circular and square patterns of 100–500 μm in size prepared by a photolithography and a chemical etching process were measured by quantitative MO imaging technique using polarization modulation technique and Bi substituted yttrium iron garne...

Magneto-optical (MO) effect is commonly used not only for an observation of magnetic domain structures, but also for a research of electrical structures in magnetic materials. In addition, distribution of a magnetic flux diverging from a magnetized sample and/or distribution of a current in the sample can be visualized with the help of an MO-indica...

MnP nanowhiskers have been grown by molecular beam epitaxy technique on the InP(100) surface. The measurements of the magnetization revealed that samples with MnP nanowhiskers exhibit ferromagnetic behavior up to room temperature. The investigation of temperature and angular dependences of ferromagnetic resonance has shown the existence of 90° anis...

Bi-substituted yttrium iron garnet, Y3-xBixFe5O12 (Bi:YIG, x = 1, 1.5), films were prepared on Gd3Ga5O12 (111) substrates by metal-organic decomposition (MOD) method to use as MO indicator films. Those films had the in-plane magnetic anisotropy and Faraday rotation as large as that of the single crystal and do not show prominent magnetic domain str...

Manganese monophosphate MnP single crystal deserves attention due to its rich magnetic phase diagram, which is quite different depending on the direction of the applied magnetic field. Generally speaking, it has a Curie temperature around 291K and several other magnetic arrangements at low temperatures (cone-, screw-, fan-, and ferromagnetic-type s...

Ge and MnP nanowhiskers have been grown by molecular beam epitaxy (MBE) concurrently on InP and GaAs substrates. The growth of MnP nanowhiskers appears to be caused by catalytic free growth mechanism, whereas the growth of Ge nanowhiskers is found to be amenable to vapour‐liquid‐solid (VLS) mechanism of growth. The measurements of temperature and...

A streak-camera system for the observation of high-speed crystallization processes induced by laser irradiation in phase-change (PC) recording materials has been developed. A distinct difference in the time-sequential development of the crystallized region was observed in two different types of PC materials, i.e., Sb78Te22 (eutectic composition) an...

High-quality thin films of Ni1-xPtx alloys have been investigated as materials for temperature sensors with a high temperature coefficient of resistance (TCR). Since the high TCR of Ni has been attributed to the spin-disordered scattering occuring just below the Curie temperature (TC), we considered that a higher TCR can be obtained by decreasing T...

Regularly aligned arrays of submicron-sized Y-shaped permalloy (Ni80Fe20) structures buried in silicon wafers have been fabricated. Spin distributions of the surface have been observed using a magnetic force microscope (MFM) and analyzed by a micromagnetic simulation based on the Landau–Lifshitz–Gilbert equation. In widely-spaced linear arrangement...

A magneto-optical (MO) microscope that uses the polarization modulation method has been developed for quantitative MO imaging. In this technique, images of MO rotation and ellipticity are reconstructed from three images for different polarization states; i.e., linear, right-circular, and left-circular polarization states. The three polarization sta...

Deposition of magneto-optical film directly on superconducting layer has been studied in order to improve the spatial resolution and the magnetic sensitivity in a magneto-optical (MO) imaging of single vortices. Calculation of MO effect in Y2BiFe5O12 (Bi:YIG)/Bi2Sr2CaCu2O8+x (BSCCO)/SrTiO3 (STO) structure was carried out using the virtual optical c...

Micrometer size patterns of Bi2Sr2CaCu2O8+x (BSCCO) and SrTiO3 (STO) films were successfully prepared on STO substrates using lift-off technique combined with metal-organic decomposition (MOD) method without any vacuum processes. The minimum size of the pattern obtained was 3μm for BSCCO and 5μm for STO. The BSCCO film after patterning showed an X-...

Ge and MnP nanowhiskers were synthesized by molecular-beam epitaxy technique on InP(001) surface concurrently. The growth of Ge nanowhiskers is found to be assisted by Mn-based nanocluster-mediated vapour-liquid-solid mechanism of growth, whereas the growth of MnP nanowhiskers seems to be caused by catalyst-free mechanism. Magnetic property measure...

Regularly aligned arrays of magnetic nano dots buried in silicon wafers have been fabricated using damascene technique with the help of electron beam lithography. Arrays of square, rectangular, cross-shaped and Y-shaped structures of submicron size have been obtained. Spin distributions have been observed by means of magnetic force microscopy and a...

A dynamic observation system for high speed crystallization has been developed using blue LD, high speed LD driver, streak camera and precise timing controller. We succeeded in dynamic observation of the crystal growth process of phase change materials induced by laser irradiation. The time-sequential development of crystallized region differs clea...

Surface morphology of Bi2Sr2CaCu2Ox (BSCCO) thin films prepared by metalorganic decomposition (MOD) method is successfully improved by using nano-structured SrTiO3 (STO) buffer layer prepared by MOD method. The nano-structured STO thin films were obtained by 2-step thermal treatment at 870C for 2 hours followed by high temperature of 1000C in O2 at...

In this paper, we report on the observed magnetic spin structure and the micromagnetic simulation of Y-shaped permalloy (Ni80Fe20) arrays. The arrays were fabricated using the damascene technique, with electron-beam lithography. For a widely separated linear arrangement, magnetic poles are observed on the ends of two of three arms of the Y-shaped a...

BixY3−xFe5O12 thin films have been grown on GGG (Gd3Ga5O12) (111) substrates by the combinatorial composition-spread techniques under substrate temperature (Tsub) ranging from 410 to 700°C and O2 pressure of 200mTorr. In order to study the effect of substrates on the deposition of BixY3−xFe5O12 thin films, garnet substrates annealed at 1300°C for 3...

Regularly aligned arrays (linear and honeycomb arrangements) of Y-shaped Ni80Fe20 (permalloy) nanodots buried in silicon wafers were fabricated using the damascene technique, and electron beam lithography (EB). The distributions of surface magnetization were observed by means of magnetic force microscopy (MFM), and the internal spin distributions w...

Polarization modulation technique has been applied for magneto-optical (MO) imaging to measure MO values quantitatively. In this paper, we report on a real-time MO imaging using the polarization modulation method with a liquid crystal modulator. Measurements of MO images and hysteresis Kerr loop of patterned Bi,Ga substituted yttrium iron garnet fi...

Novel ternary Mn-containing compound MnGeP2 has been grown on GaAs and InP substrates using molecular beam epitaxy, in which Mn and Ge were supplied from solid sources and P from a gas source. The films obtained showed XRD pattern characteristic of MnGeP2. Lattice constants were determined using reciprocal lattice mapping analysis. Films directly g...

Epitaxial growth of the Mn-containing novel ternary compound MnGeP2 has been investigated. Prior to the growth experiments, theoretical studies using an ab initio calculation were carried out, on the basis of which the stable existence of MnGeP2 with a chalcopyrite structure was predicted. Growth experiments of Mn-Ge-P were performed on GaAs(001) a...

Bi₂Sr₂CaCu₂O_x(BSCCO)/SrTiO₃(STO)/BSCCO trilayer structures were prepared by the metal-organic decomposition (MOD) method. In this study, annealing condition of BSCCO thin films prepared by the MOD method were investigated. High quality films having critical temperature (Tc) of 84 K were obtaine...

Magneto-optical (MO) imaging of a Bi:YIG film was carried out using a liquid crystal (LC) as an optical modulator. Magnetic domain structure indicating a perpendicular magnetic anisotropy is clearly observed in a Faraday image of the film. An ellipticity image is also obtained from the same three images used for the Faraday images. This result show...

MnGeP₂ and MnP thin films are grown on GaAs substrates using molecular beam epitaxy technique and their magnetic properties are compared. The easy axis of magnetization in MnGeP₂ is in-plane and that of MnP is perpendicular. Results indicate the magnetic anisotropy of the two samples is different and both show ferromagnetic be...

Epitaxial growth of a novel chalcopyrite-type MnGeP2 has been investigated using an MBE technique. In order to improve the surface morphology of the films, an effect of introduction of a Ge buffer layer was investigated. This results in dramatic change of the RHEED pattern from spotty to streaky ones. Improvement of surface morphology was confirmed...

This paper describes the observed magnetic structure and the micromagnetic simulation of cross-shaped, permalloy (Ni80Fe20) arrays embedded in silicon wafers. The nano-scale-width, cross-shaped patterns were fabricated using the damascene technique, electron beam lithography, and chemical mechanical polishing. The magnetic poles were observed as tw...

Novel ternary compound MnGeP2 thin films have been prepared on InP(0 0 1) substrates by molecular beam epitaxy (MBE), in which Mn and Ge were supplied from solid sources using Knudsen cells and P-2 from a gas source by decomposing tertiary butyl phosphine (TBP). From an X-ray analysis the crystal structure was determined to be tetragonal with latti...

Growth conditions for MnGeP2 thin films have been investigated by using molecular beam epitaxy (MBE) method. Mn and Ge were evaporated by K-cells, and P2 was supplied by decomposing tertialybutylphosphine (TBP). GaAs (001) and InP (001) single crystals were used as substrates. An X-ray diffraction peak, which can be assigned to (008) peak of MnGeP2...

Bi- and Ga-substituted rare-earth iron garnet (Re,Bi)3(Fe,Ga)5O12 (ReY, Gd and Nd) thin films were fabricated on glass, Si(1 0 0) and GGG(1 1 1) substrates using the metal organic decomposition (MOD) method, in which the metal-organic solution is spin-coated, dried, and sintered. Thin films with a garnet single phase were successfully obtained for...

Epitaxial (Y,Bi){sub 3}(Fe,Ga){sub 5}O{sub 12} garnet thin films have been prepared on Gd{sub 3}Ga{sub 5}O{sub 12} (111) substrates by a metal-organic decomposition (MOD) method using carboxylic acids. The chemical compositions of the films prepared in this study are Y{sub 2}BiFe{sub 5}O{sub 12} (YBFO), Y{sub 3}Fe{sub 4}GaO{sub 12} (YFGO), and Y{su...

Magnetic nanostructures embedded in silicon wafers were successfully fabricated by the damascene technique using electron beam lithography. The magnetic properties of embedded square dots (1μm in width and 100nm in height), rectangular dots (300nm×100nm in area and 100nm in height), and circular dots (100nm in diameter and 100nm in height) were inv...

A new magneto-optical (MO) imaging system for high-throughput characterization of combinatorial magnetic thin films has been developed. The instrument allows us to measure both Faraday rotation and ellipticity maps at various wavelengths, and at different magnetic fields for wide variety of materials. We confirmed that the system possesses enough s...

Reflectivity and magneto-optical Kerr spectra are measured in epitaxial FePt films prepared under reduced substrate temperatures. From these spectra off-diagonal elements of conductivity tensor was calculated. By comparison with those prepared under conventional preparation conditions, the L1 0 -ordered FePt films prepared at reduced temperatures p...

Magneto-optical microscope utilizing polarization modulation technique was developed to obtain magnetooptical (MO) images involving quantities of MO effects, such as Faraday rotation and ellipticity. Faraday rotation images were calculated 'from three images taken with a linear polarized light and circularly polarized lights with left and right rot...

High T_{c} superconducting B i_2S r_2CaC u_2O_{8 d} (BSCCO2212) films were prepared by a metallorganic decomposition (MOD) method. The metal organic solution of BSCCO2212 was spin-coated on MgO (100) substrates at 3000 rpm for 1 min. To achieve a high critical current density, we controlled heat-treatment conditions and atmosphere. The films were a...

Five-nanometer-thick Fe film has been grown on self-organized SrTiO3(001) substrate with an inclined angle (alpha). The morphology of Fe film was investigated by scanning tunneling microscopy (STM). Dependence of the magnetic property on the inclined angle was revealed by magneto-optic Kerr effect (MOKE) measurement. In the morphology of Fe film, t...

EPR and PL spectra were measured to investigate point defects in I–III–VI2 type chalcopyrite semiconductors where the group I element is Cu. Taking into account various optical spectra, the EPR signals observed were assigned to defect centers involving residual Fe impurities and Cu-vacancies. Some of the point defects were found to form defect-comp...

Heavily Mn-doped II–VI–V2 semiconductors, such as CdGeP2 and ZnGeP2 have been prepared by depositing Mn on single crystalline substrate at nearly 400 °C in an ultra high vacuum chamber. Well-defined ferromagnetic hysteresis with a saturation behavior appears in the magnetization curve up to above room temperature. The chemical states of the ZnGeP2:...

The chemical states of the ZnGeP(2):Mn interface which shows ferromagnetism above room temperature have been studied by photoemission spectroscopy. Mn deposition on the ZnGeP2 substrate heated to 400 degrees C induced Mn substitution for Zn and then the formation of metallic Mn-Ge-P compounds. Depth profile studies have shown that Mn 3d electrons c...

We report the nonequilibrium effect of polaronic quasiparticle (QP) injection using an organic injector in a high T_c three terminal device. The organic, copper (II) phthalocyanine (Cu-Pc), used as the injector, is a photoconductor and a p-type semiconductor. The transport properties of Au/Cu-Pc/Bi₂Sr₂CaCu<sub>2</sub...

Co-alloy single-crystal thin films were prepared on SrTiO3(1 1 1), LaAlO3(0 0 0 1), and Al2O3(0 0 0 1) substrates. The film structure was studied using X-ray diffraction and high-resolution transmission electron microscopy. It is shown that epitaxial growth of a CoCrPt magnetic layer strongly depends on the substrate and underlayer materials.