Publications (69)120.5 Total impact
- [Show abstract] [Hide abstract] ABSTRACT: Surface ferromagnetic state of FeRh thin films irradiated with 1 keV Ar ion-beam has been investigated by using soft X-ray Magnetic Circular Dichroism (XMCD). It was revealed that the Fe atoms of the samples were strongly spin-polarized after Ar ion-beam irradiation. Due to its small penetration depth, 1 keV Ar ion-beam irradiation can modify the magnetic state at subsurface of the samples. In accordance with the XMCD sum rule analysis, the main component of the irradiation induced ferromagnetism at the FeRh film surface was to be effective spin magnetic moment, and not to be orbital moment. We also confirmed that the surface ferromagnetic state could be produced by thermal annealing of the excessively ion irradiated paramagnetic subsurface of the FeRh thin films. This novel magnetic modification technique by using ion irradiation and subsequent annealing can be a potential tool to control the surface magnetic state of FeRh thin films.
- [Show abstract] [Hide abstract] ABSTRACT: Ferromagnetic layered structure has been made at sub-surface of the antiferromagnetic FeRh bulk samples by high energy He ion beam irradiation. In accordance with the Transport of Ions in Matter simulation, such ion beam can effectively deposit the elastic collision energy in several μm regions in the depth from the surface. Measurement with a superconducting quantum interference device reveals the irradiated samples to be ferromagnetic. Assuming that only the part the energy deposited can be modified to be ferromagnetic, the corresponding irradiation induced magnetization is consistent with the data that we previously reported. On the other hand, the X-ray magnetic circular dichroism (XMCD) spectra for the irradiated samples are totally unchanged as those for the unirradiated samples. Since XMCD signal in total emission yield method is considered to be surface sensitive with a typical probing depth of several nm, the surface magnetic state is maintained to be antiferromagnetic. By utilizing these phenomena, three-dimensional magnetic patterning of FeRh can be realized, which may potentially be used for future magnetic exchange device application such as nano-scale sensors and memories.
- [Show abstract] [Hide abstract] ABSTRACT: The effect of energetic cluster ion beam irradiation on magnetic and structural properties of FeRh thin films have been investigated. The cluster ions used in the present studies consist of a few gold atoms with the energy of 1.67 MeV/gold atom. Saturation magnetization of the sample irradiated with Au3 cluster ion beam (280 emu/cc) is larger than that for the irradiated sample with Au1 ion beam (240 emu/cc) for the same irradiation ion fluence. These results can also be confirmed by the X-ray magnetic circular dichroism (XMCD) measurement; the XMCD signal for Au3 cluster ion irradiation is larger than that for Au1 ion irradiation. Since the ion beam irradiation induced magnetization of FeRh is significantly correlated with the amount of the lattice defects in the samples, cluster ion beam irradiation can be considered to effectively introduce the lattice defects in B2-type FeRh rather than the single ion beam. Consequently, cluster ion irradiation is better than single ion irradiation for the viewpoint of saturation magnetization, even if the same irradiation energy is deposited in the samples.
- [Show abstract] [Hide abstract] ABSTRACT: We revealed that the Ba(Co0.85Mn0.15)O3-δ ceramic samples exhibited ferromagnetic-dielectric behavior below the magnetic transition temperature of about 35 K. The origin of their magnetic ordering was expected to super-exchange coupling of Co(4+)(d (5))-O(2-)-Mn(4+)(d (3)) with bonding angle of 180° and/or Mn(4+)(d (3))-O(2-)-Mn(4+)(d (3)) with bonding angle of 90°. The magnetic spin momentum estimated by the magnetic Compton profiles (MCP) of the samples had similar temperature dependence as that determined by the temperature dependence of magnetic moment by superconducting quantum interference device, which meant that the observed magnetic moments could be ascribed to the spin moment. The shapes of the MCPs of the samples were completely same regardless of the temperature measured. This result indicates that there are no changes of the momentum space distribution of spin density between ferromagnetic and paramagnetic states. So, this magnetic transition is simply caused by a thermal fluctuation of the spin.
- [Show abstract] [Hide abstract] ABSTRACT: We have studied the magnetic properties of pure CeO2 irradiated with swift heavy ions. Experimental results showed that the ferromagnetism was induced even at room temperature by 200 MeV Xe ion irradiation. The value of saturation magnetization, Ms, systematically changes as a function of ion-fluence. The value of Ms increases with increasing the ion-fluence and reaches a maximum value at about the fluence of 2.0 × 1013/cm2, and then decreases. The X-ray diffraction (XRD) spectra show that the lattice constant of CeO2 increases with increasing ion-fluence. This result and our previous XPS result show that the ion-irradiation produced oxygen vacancies. The present study implies that the ferromagnetic behavior of the ion-irradiated CeO2 is attributed to the magnetic moments of localized 4f electrons on Ce3+ atoms, which are related to oxygen vacancies.
- [Show abstract] [Hide abstract] ABSTRACT: To study the effects of Gd2O3-doping and the irradiation with high energy fission products in the nuclear fuels (UO2), Gd2O3-doped CeO2 pellets, which are simulation materials of UO2, were irradiated with 200 MeV Xe14+ ions. Effects of Gd2O3-doping and the ion irradiation were estimated by using Extended X-ray Absorption Fine Structure (EXAFS) measurement. The interatomic distances between each Ce and the first nearest O atoms, and Ce and the second nearest Ce atoms increase by the irradiation and the effect of the ion irradiation on the atomic distances is more pronounced for higher amounts of dopant. The Debye–Waller factors for Ce–O and Ce–Ce pairs increase with increasing the amount of Gd2O3 dopant. These results suggest that the lattice binding energy is weakened by Gd2O3-doping. The Debye–Waller factors increase also by the irradiation. The effect of ion irradiation on the Debye–Waller factors, however, becomes smaller for higher amounts of dopant.
- [Show abstract] [Hide abstract] ABSTRACT: Low temperature ferromagnetic FeRh with B2-type crystal structure was successfully synthesized by annealing of the excessively irradiated FeRh thin film samples having nonmagnetic A1-type crystal structure. The B2 phase transformed from the A1 phase by this process contained some amount of lattice defects, such as anti-site defects and vacancies, which made the magnetic spins of the sample aligned. These results imply that the combination of the process of the ion-beam irradiation and annealing of the film samples makes the magnetic state systematically controlled.
- [Show abstract] [Hide abstract] ABSTRACT: FeRh thin films were irradiated with a 10 MeV iodine ion microbeam to produce micrometre-scale ferromagnetic microstructures by modifying the local magnetic character from antiferromagnetism to ferromagnetism using ion-microbeam irradiation. Two-dimensional magnetic dot arrays of dimensions ∼2 µm × 4 µm as well as 10 µm × 10 µm were successfully produced on the FeRh surface, which was confirmed by magnetic force microscopy (MFM). The results of photoemission electron microscopy (PEEM) combined with X-ray magnetic circular dichroism reveal that the easy axis of the magnetization of the ion-beam-irradiated ferromagnetism in the FeRh thin films lies in the film planes along the <001> direction of the MgO substrates.
- [Show abstract] [Hide abstract] ABSTRACT: Effects of thermal annealing on ion-irradiation induced ferromagnetism of Fe–50at.%Rh bulk alloy and the related structural change were investigated by means of superconducting quantum interference device (SQUID) and extended X-ray absorption fine structure (EXAFS), respectively. Depending on the annealing temperature from 100 to 500 °C, the magnetization induced by 10 MeV iodine ion irradiation and the lattice structure of the alloy were remarkably changed. After 500 °C annealing, the magnetization and the lattice ordering of the alloy become similar to the states before the irradiation. The experimental result indicates that the thermal relaxation of irradiation-induced atomic disordering dominates the magnetic state of ion-irradiated Fe–50at.% Rh alloy.
- [Show abstract] [Hide abstract] ABSTRACT: To simulate the effects of Gd2O3-doping and high-energy fission products in UO2, Gd2O3-doped CeO2 pellets were irradiated with 200-MeV Xe14+ ions. Doping and irradiation effects were analyzed using X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS). The lattice constant of CeO2 decreases and the local structure is disordered with increased doping levels. However, the irradiation induces an expansion of the lattice and a disordering of atomic arrangement near the Gd atoms. The effects of the irradiation become more pronounced with increasing Gd2O3-dopant levels. Our results are compared with those of a study involving Er2O3-doped CeO2.
- [Show abstract] [Hide abstract] ABSTRACT: The magnetic Compton profiles of Fe-50 at. % Rh intermetallic compound were measured to study the ferromagnetism induced by 200 MeV Xe ion irradiation. The magnetic effect at 50 K increases with increasing the ion-fluence. The analysis of the experimental result revealed that the values of spin moment induced by the irradiation were close to the values of magnetization obtained by a superconducting quantum interference device magnetometer, suggesting that the ion irradiation mainly induces the spin magnetic moment. The difference in magnetic Compton profiles between the irradiation-induced ferromagnetism and the intrinsic ferromagnetism in pure Fe is also discussed.
- [Show abstract] [Hide abstract] ABSTRACT: We investigated a low-energy ion-beam irradiation process for the magnetic modification of FeRh thin films using a focused ion beam system. Low-energy ion-beam irradiation induced ferromagnetic states in the FeRh thin films at low temperatures, that originally exhibited antiferromagnetism, as effectively as high-energy ion-beam irradiation. Because the energy deposited by the elastic collisions caused by the irradiation determined the magnetic properties of the samples, the magnetic state of the FeRh thin films could be quantitatively controlled. The low-energy ion-beam irradiation using a focused ion beam system is a potential technique to modify the magnetic properties of materials on the nano- and micro-scales, which may lead to a variety of novel spin devices and applications.
- [Show abstract] [Hide abstract] ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
- [Show abstract] [Hide abstract] ABSTRACT: The epitaxially grown Ba(Fe0.2Zr0.8)O3-delta (BFZO) films with various thicknesses ranging from 30 to 170 nm were successfully synthesized on (001)SrTiO3 (STO) substrates by a pulsed laser-beam deposition method. The results of x-ray diffraction and transmission electron microscopy revealed that all the films exhibited the epitaxial relationship of (100)BFZO||(100)STO and BFZO||STO. In addition, 0.7% expansion of the a-axis lattice constant in the films with over 100 nm thickness was measured. Although all the BFZO films showed ferromagnetic and dielectric natures even at room temperature, the magnetization values were found to be significantly dependent upon the film thickness. The magnetization values of the films with a thickness over 100 nm films were fairly decreased rather than those of the smaller thickness films. In accordance with the x-ray photoelectron spectroscopy measurement, the decrease in the magnetization was mainly ascribed to the decreased number of the tetravalent Fe ions, which was caused by the relaxation of the misfit strain between the film and substrates.
- [Show abstract] [Hide abstract] ABSTRACT: Changes in magnetic properties and lattice structure of FeRh films by 180 keV-10 MeV ion (H, He, and I) irradiation are studied. In spite of the irradiation with different ion species and wide range of energies, the changes in magnetization are dominated by solely a single parameter; the density of energy which is deposited through elastic collision between the ions and the samples. For the low deposition energy density, the magnetization increases with increasing the deposition energy density, while the lattice structure remains unchanged. When the deposition energy density becomes larger, however, the magnetization decreases after reaching the maximum value. The decrease in the magnetization accompanies the crystal structure change from B2 to A1. The present results imply that the magnetic state of FeRh films can be designedly controlled by the energetic ion irradiations.
- [Show abstract] [Hide abstract] ABSTRACT: The influence of coprecipitated barium ferrite (BaF) on the magnetic and mechanical properties of natural rubber–ferrite composites (RFCs) has been studied. Unusual characteristics of the BaF particles were revealed by a scanning electron microscope. The results show that the saturation magnetisation increases with increasing the ferrite content even for the considerably high BaF loading samples, whereas the coercivity is almost unchanged. The present RFCs recorded relatively low density 1·95 g cm?3 with high stored energy 1·26 MGOe at the maximum BaF loading of 220 phr. Both of the tensile strength and the elongation at break decrease with increasing BaF content. Evaluation of the swelling ratio was carried out to have an insight into the change in the mechanical properties of the RFCs at high BaF loading.
- [Show abstract] [Hide abstract] ABSTRACT: Thin films of Mn2−xCrxSb with x=0.06 were synthesized by solid-state reaction of the ion beam sputtered Mn/Cr/Mn/Sb multilayers on SiO2 substrates. The films were irradiated at room temperature with 10MeV iodine ions by using a tandem accelerator at JAEA-Takasaki. The temperature dependence of the magnetization measured at 10kOe apparently showed the antiferromagnetic-ferrimagnetic phase transition at around 200K for the unirradiated x=0.06 samples. After the samples were irradiated up to 1.0×1014ions/cm2, the transition temperature was apparently shifted toward a higher temperature side for about 12.8K. However, notable structural changes could not be found due to the ion irradiations. These results suggest that the energetic heavy ion irradiation for the magnetic thin films with a first-order phase transition significantly affects the phase transition temperature with the transferred energy by the ion irradiation process.
- [Show abstract] [Hide abstract] ABSTRACT: Fe–50at.%Rh bulk alloys were irradiated with 10MeV 127I, 60MeV 136Xe and 200MeV 136Xe ions at room temperature. Effects of the ion irradiation on magnetic properties were measured by using superconducting quantum interference device (SQUID). By comparing the results for higher energy (60 and 200MeV) ion irradiation with that for lower energy (10MeV) irradiation, we have obtained the linear relationship between the irradiation-induced magnetization and the deposited energy density though the elastic collisions. This relationship can be used for the quantitative modification of low temperature magnetism of Fe–50at.%Rh alloy.
- [Show abstract] [Hide abstract] ABSTRACT: Ba(Fe0.2Zr0.8)O3-delta (BFZO) films were synthesized on Si(001) substrates using SrTiO3 (STO) buffer layers by pulsed laser-beam deposition method. The results of the x-ray diffraction revealed that the STO buffer layers and the BFZO films had polycrystalline nature. The STO-buffered BFZO films showed ferromagnetic hysteresis loops at room temperature, and their saturation magnetization was 3.3 times as large as that of the BFZO films directly deposited on Si(001) substrates. The STO-buffered BFZO films partially grew epitaxially on the STO buffer layers with orientation relationships. The results of the x-ray photoelectron spectroscopy analysis using soft x-ray radiation indicated that the relative amount of the Fe4+ ions fairly increased for the STO-buffered BFZO films rather than for the BFZO films directly deposited on Si substrates.
Osaka Prefecture University
Sakai, Ōsaka, Japan
- • Research Organization for the 21st Century
- • Department of Materials Science
- • Graduate School of Engineering
- • College of Engineering