Munetoshi Seki

Fabrication of Aligned Magnetic Nanoparticles Using Tobamoviruses

We used genetically modified tube-shaped tobamoviruses to produce 3 nm aligned magnetic nanoparticles. Amino acid residues facing the central channel of the virus were modified to increase the number of nucleation sites. Energy dispersive X-ray spectroscopy and superconducting quantum interference device analysis suggest that the particles consisted of Co-Pt alloy. The use of tobamovirus mutants is a promising approach to making a variety of components that can be applied to fabricate nanometer-scaled electronic devices.

Enhanced Photocurrent in Rh-Substituted α-Fe2O3 Thin Films Grown by Pulsed Laser Deposition

Rh-substituted α-Fe2O3 (Fe2-xRhxO3; 0.0≤x≤2.0) thin films were grown on α-Al2O3(110) substrates with a Ta-doped SnO2 electrode layer by pulsed laser deposition. Highly oriented epitaxial films with pure corundum structures were successfully fabricated over the entire compositional range. The optical absorption spectra of the films indicate narrowing of the bandgap with increasing Rh content. Consequently, the photoelectrochemical performance was improved in the Rh-substituted films. We found that the optimum Rh content lies at around x=0.2, where the photocurrent is significantly enhanced over a wavelength range of 340–850 nm.

Investigation of the sol-gel transition of gelatin using terahertz time-domain spectroscopy

The sol-gel transition temperature of gelatin is determined using viscoelasticity measurement and terahertz time-domain spectroscopy. From the results of the viscoelasticity measurement, the sol-gel transition temperature is determined to be 30–32 °C, and it strongly depended on the concentration. However, terahertz time-domain spectroscopy indicates a particular transition temperature of 36 °C. A distinction of these transition temperatures is attributed to the difference in the structural changes detected by these measurements.

High spin polarization at room temperature in Ge-substituted Fe3O4 epitaxial thin film grown under high oxygen pressure

Epitaxial thin films of room-temperature ferrimagnetic (Fe,Ge)3O4 were fabricated using pulsed laser deposition. Films with a single-phase spinel structure were grown under high oxygen pressures (0.01–0.6 Pa). The carrier transport across (Fe,Ge)3O4/Nb:SrTiO3 interface was studied to estimate the spin polarization of (Fe, Ge)3O4. Current–voltage curves of Fe2.8Ge0.2O4/Nb:SrTiO3 junction showed rectifying behavior even at 300 K whereas Fe3O4/Nb:SrTiO3 junction showed ohmic behavior. Calculations based on a model for a Schottky contact with a ferromagnetic component yielded a spin polarization of 0.50 at 300 K for Fe2.8Ge0.2O4, indicating its potential as a promising spin injector.

Solid–liquid-type solar cell based on α-Fe2O3 heterostructures for solar energy harvesting

Photoelectrochemical cells based on Rh-substituted α-Fe2O3 films were fabricated by pulsed laser deposition. The optical bandgap of the films was found to decrease with increasing Rh content. X-ray photoemission spectroscopy analysis revealed that the bandgap narrowing in Rh-substituted films is caused by the hybridization of the Rh t2g band with the valence band of α-Fe2O3 near the Fermi level. As a result, the photoelectrochemical performance was improved in the Rh-substituted films in the visible and near-infrared regions. The photocurrent in films with a high orientation along the [110] direction was significantly larger than that in the polycrystalline films, which is possibly attributed to the anisotropic electrical conduction of α-Fe2O3.

Epitaxial Thin Films of InFe2O4 and InFeO3 with Two-Dimensional Triangular Lattice Structures Grown by Pulsed Laser Deposition

Single-crystalline thin films of indium iron oxides with two-dimensional triangular lattice structures were successfully grown on ZnO(001) substrates using pulsed laser deposition. Thin films of ferrimagnetic InFe2O4 with uniaxial magnetic anisotropy were found to grow in vacuum, while weak-ferromagnetic InFeO3 thin films were formed under O2 atmosphere. The key point for the growth of high-quality films is the control of volatilization of In during film deposition, which can be achieved by changing the growth temperature, O2 pressures, and target compositions.

Photoemission and x-ray absorption studies of valence states in (Ni,Zn, Fe,Ti)3O4 thin films exhibiting photoinduced magnetization

By means of photoemission and x-ray absorption spectroscopy, we have studied the electronic structure of (Ni,Zn,Fe,Ti)3O4 thin films, which exhibits a cluster glass behavior with a spin-freezing temperature Tf of ∼230K and photoinduced magnetization (PIM) below Tf. The Ni and Zn ions were found to be in the divalent states. Most of the Fe and Ti ions in the thin films were trivalent (Fe3+) and tetravalent (Ti4+), respectively. While Ti doping did not affect the valence states of the Ni and Zn ions, a small amount of Fe2+ ions increased with Ti concentration, consistent with the proposed charge-transfer mechanism of PIM.By means of photoemission and x-ray absorption spectroscopy, we have studied the electronic structure of (Ni,Zn,Fe,Ti)3O4 thin films, which exhibits a cluster glass behavior with a spin-freezing temperature Tf of ∼230K and photoinduced magnetization (PIM) below Tf. The Ni and Zn ions were found to be in the divalent states. Most of the Fe and Ti ions in the thin films were trivalent (Fe3+) and tetravalent (Ti4+), respectively. While Ti doping did not affect the valence states of the Ni and Zn ions, a small amount of Fe2+ ions increased with Ti concentration, consistent with the proposed charge-transfer mechanism of PIM.

Long-term potentiation of magnonic synapses by photocontrolled spin current mimicked in reentrant spin-glass garnet ferrite Lu3Fe5−2xCoxSixO12 thin films

(Co,Si)-cosubstituted Lu3Fe5O12 (Lu3Fe5−2xCoxSixO12; 0.00 ≤ x ≤ 1.00) thin films were grown on Y3Al5O12(001) substrates by pulsed laser deposition. Reentrant spin-glass behavior was observed and its robustness against external magnetic fields was improved by increasing the Co–Si content. In contrast, the spectral linewidth of ferromagnetic resonance was broadened by increasing the Co–Si content, which indicates that the Lu3Fe4.8Co0.1Si0.1O12 thin film is an optimal spin-glass spin-wave conductor. The spin pumping voltage of Lu3Fe4.8Co0.1Si0.1O12 exhibited short-term plasticity with photoinduced magnetic anisotropy and long-term potentiation with the photomemory effect, which mimicked the pre- and postsynaptic potentials of biological systems.

Epitaxial thin films of p-type spinel ferrite grown by pulsed laser deposition

Epitaxial thin films of Ge-substituted Fe3O4 were grown on α-Al2O3 (001) using pulsed laser deposition, and their electrical and magnetic properties were investigated. A target with excess Ge compositions was employed for the film growth to compensate for the volatilization of germanium oxides during the high-temperature deposition. P-type conduction was achieved for the Ge-rich films. The Neel temperature of all the films was above 300 K. Furthermore, the films exhibited an anomalouos Hall effect at 300 K, suggesting that the carriers in the films are spin-polarized.

Room-temperature-photoinduced magnetism and spin-electronic functions of spinel ferrite with a spin-cluster structure

Room-temperature-photoinduced magnetization (PIM) was observed in spinel ferrite Al0.2Ru0.8Fe2O4 thin films with a spin-cluster-glass structure. Additionally, the films exhibited significant properties as spintronic materials, showing a low saturation magnetization under 0.6μB/unit cell and good conductivity with a high spin polarized electron level of over 75%. A combination of high-temperature PIM and the electronic properties associated with spintronics would generate an area of research and development that utilize the degrees of freedom offered by optical systems in the field of spintronics.