Hiroyasu Yamahara

• The University of Tokyo

This study investigates the effects of epitaxial strain on the crystal structure, magnetization, and spin wave propagation characteristics of rare-earth iron garnet thin films. Thin films of Y3Fe5O12 (YIG) and Lu3Fe5O12 (LuIG), each with identical thicknesses, are grown on Gd3Ga5O12 (GGG), substituted Gd3(GaMgZr)5O12 (SGGG), and Y3Al5O12 (YAG) subs...

Recent progress in gas‐sensing technology has enabled the rapid collection and highly sensitive analysis of skin gases associated with body odour. Skin gases can be collected less invasively, more continuously, and less consciously than blood or urine. Patients with end‐stage kidney disease (ESKD) have a characteristic uremic odour that fades after...

Substituting rare‐earth Eu ions with a large atomic number into 3d transition metal oxides can precisely control their magnetic properties through significant spin‐orbit coupling, leading to noncollinear magnetism. Experimental investigations are combined with density functional theory to explore site‐selective Eu³⁺ substitution as a strategy to en...

Rare‐earth iron garnets (RIG, R3Fe5O12) are insulating ferrimagnets with high inversion symmetry because of their centrosymmetric cubic crystal structure. However, this high centrosymmetry can be reduced by introducing a non‐uniform strain, leading to a tetragonally distorted lattice structure. In this study, the strain‐induced lattice distortions...

Detection of parts-per-trillion (ppt)-level acetone gas molecules at room temperature using suspended graphene on SiO2 micropillars has rarely been achieved using solid-state devices or surface acoustic wave (SAW) sensors. This paper presents the effect of SiO2 micropillars and suspended graphene as a guiding and sensing layer to detect acetone gas...

Surface acoustic wave (SAW) sensors are widely used in sensing technology owing to their high sensitivity, stability and ability to detect various physical, chemical and biological properties. They operate by detecting changes in the velocity and amplitude of acoustic waves travelling along piezoelectric materials, which are influenced by environme...

The temperature dependence of the dielectric properties and phonon behavior of gadolinium gallium garnet (GGG) and yttrium aluminum garnet (YAG) single crystals were analyzed by terahertz time-domain spectroscopy (THz-TDS), Fourier transform infrared spectroscopy (FT-IR), and density-functional-theory (DFT) calculations. A custom air-plasma-based T...

Temperature dependence of the lowest frequency transverse optical phonon (TO1) in a single crystal Substituted Gadolinium Gallium Garnet (SGGG, (001)) was studied using terahertz time-domain spectroscopy at temperatures between 80 K and 500 K. The complex dielectric constants were calculated from the optical constants fitting with the Lorentz oscil...

Spin waves (SWs) stand out as one of the most promising candidates for post-complementary metal-oxide semiconductor (CMOS) computing devices owing to their data transmission capability that is devoid of Joule heating and their inherent wave nature. However, realizing an electric-field-based, energy-efficient, and scalable control mechanism for both...

A Pb(Zr0.52Ti0.48)O3 (PZT) thin film is fabricated on SrRuO3(SRO)/Pt/ZrO2/Si, and its resistive switching properties are thoroughly investigated. The ZrO2 thin film serves as a buffer layer for the epitaxial growth of single‐crystalline PZT thin films, and spin‐coating fabrication is useful for introducing a suitable defect content to achieve effec...

In spin wave (SW) devices, the modulation of SWs for computational units is necessary, imposing extremely high demands on material systems. In this study, high‐quality epitaxial‐grown spinel γ‐Fe2O3 thin films on conductive Nb‐doped SrTiO3 substrates, achieving fast‐speed, high‐frequency, and long‐distance SW propagation in this ferrimagnetic mater...

Gain‐dissipative Ising machines (GIMs) are annealers inspired by physical systems such as Ising spin glasses to solve combinatorial optimization problems. Compared to traditional quantum annealers, GIM is relatively easier to scale and can save on additional power consumption caused by low‐temperature cooling. However, traditional GIMs have a limit...

Gain-dissipative Ising machines (GIMs) are dedicated devices that can rapidly solve combinatorial optimization problems. The noise intensity in traditional GIMs should be significantly smaller than its saturated fixed-point amplitude, indicating a lower noise margin. To overcome the existing limit, this work proposes an overdamped bistability-based...

Spin waves (SW) stand out as one of the most promising candidates for post-complementary metal-oxide semiconductor (CMOS) computing devices owing to their data transmission capability that is devoid of Joule heating and their inherent wave nature. However, realizing an electric-field-based, energy-efficient, and scalable control mechanism for both...

To improve the quality of modern life in the current society, low-power, highly sensitive, and reliable healthcare technology is necessary to monitor human health in real-time. In this study, we fabricated partially suspended monolayer graphene surface acoustic wave gas sensors (G-SAWs) with a love-mode wave to effectively detect ppt-level acetone...

The development of semiconductor gas sensors has potential applications in breath analysis to realize noninvasive health monitoring. Herein, tin oxide (SnO2) and copper oxide (CuO) heterocomposite nanofibers were fabricated by electrospinning Sn and Cu precursors on Si substrates, followed by calcination of sensing ammonia (NH3) with high sensitivi...

Logical stochastic resonance (LSR) system is a physical system capable of performing robust reconfigurable logical operations in the presence of background noise using specific nonlinearities. Traditional LSR systems are typically based on polynomial nonlinearities, which make them suitable for implementation by electronic components. However, ther...

Reservoir computing is a brain heuristic computing paradigm that can complete training at a high speed. The learning performance of a reservoir computing system relies on its nonlinearity and short-term memory ability. As physical implementation, spintronic reservoir computing has attracted considerable attention because of its low power consumptio...

Spin waves (SWs), an ultra-low power magnetic excitation in ferro or antiferromagnetic media, have tremendous potential as transport less data carriers for post-CMOS technology using their wave interference properties. The concept of magnon interference originates from optical interference, resulting in a historical taboo of maintaining an identica...

Logical stochastic resonance (LSR) is a paradigm to realize reconfigurable robust Boolean operations using specific nonlinearity in the presence of background noise. The stable-state number of the traditional LSR is less than four, which restricts its upper limit in the heavy noise floor. To further improve the noise robustness and output quality o...

Magnonics, an emerging research field that uses the quanta of spin waves as data carriers, has a potential to dominate the post-CMOS era owing to its intrinsic property of ultra-low power operation. Spin waves can be manipulated by a wide range of parameters; thus, they are suitable for sensing applications in a wide range of physical fields. In th...

The gain-dissipative Ising machine (GIM), comprising a nonlinear transfer function and spin interaction feedback, is one of the most promising quantum analog annealers. However, previous GIM constructions have been limited to only bistable nonlinear transfer functions with low noise intensity condition. To provide a new insight and broaden the pote...

Quantum Analog Annealing of Gain‐Dissipative Ising Machine Driven by Colored Gaussian Noise In article number 2100497, Zhiqiang Liao, Hiroyasu Yamahara, and co‐workers utilize noise dispersion as a hyperparameter to modulate the performance of a gain‐dissipative Ising machine. The work proves the reddening noise can suppress random spin switching,...

By combining surface-enhanced Raman spectroscopy together with resonance Raman effects in the deep-UV region, ultra-sensitive and selective molecule detection can be achieved by deep-UV surface-enhanced resonance Raman spectroscopy (SERRS). Here, we report a deep-UV plasmonic nano-eggs structure consisting of elongated Al nanoparticles on black Si...

Alteration of the hydrogen bond (H-bond) network by trehalose is acknowledged as a bioprotective agent. However, most studies exploring the hydration superiority of the trehalose structure are limited in the computation or a narrow-range spectrum. In the present study, the structural and dynamical behaviors of the H-bond network of trehalose and ma...

Polyethylene glycol (PEG) is a well-known water retention agent in biomedical products, the hydration efficiency of which is affected by its molecular weight. Using a broadband dielectric spectroscopy (100 MHz–18 THz), the hydration state of PEG aqueous solutions with various molecular weights was quantitatively evaluated. As the molecular weight i...

The physical implementation of reservoir computing (RC), a brain-inspired computing framework, is attracting increasing attention in various research fields owing to its capability of quick learning and the relatively simple training process. Although several physical RC models have been envisaged and realized, most of them require additional perip...

Gain‐dissipative Ising machines (GIMs) are a type of quantum analog equipment that can rapidly determine the optimal solution for combinatorial optimization problems. When the noise intensity is significantly lower than the fixed point of the system, the performance of a GIM is not influenced by the fluctuation of the noise intensity. However, the...

Stochastic resonance (SR) is a phenomenon wherein an information-carrying signal is enhanced via noise in a nonlinear system. This phenomenon enables living beings to adapt to noisy environments and use environmental noise to obtain useful information. A novel activation function of the echo state network (ESN) based on bistable SR is proposed in t...

Flexoelectricity is a universal property associated with dielectric materials, wherein they exhibit remanent polarization induced by strain gradient. Rare-earth iron garnets, R3Fe5O12, are ferrimagnetic insulators with useful magnetic properties. However, they are unlikely to show remanent dielectric polarization because of their centrosymmetric st...

Thin films of BaFe 1- x M x O 3 (M = Hf, Zr, and Ce; 0.0 ≤ x ≤ 0.75) were fabricated using pulsed laser deposition and their magnetic properties were investigated. X-ray diffraction analysis indicated that oxygen-deficient BaFeO x ( x < 3.0) with a monoclinic structure was formed when the deposition was conducted using a non-substituted target ( x...

The realization of ultra-low energy consumption spin wave device applications requires a material that can efficiently propagate the spin waves. Spinel-type ferrite is a promising insulator from the perspective of application in magnonic devices owing to its good crystal compatibility. In this study, thin films of spinel γ-Fe2−xAlxO3 (0 ≤ x ≤0.5) a...

Superparamagnetic tunnel junctions (STJs) are nanostructures with very low turnover barriers. The barrier height of an STJ is generally equal to the heat energy at room temperature; thus, it can oscillate automatically without external driving. Previous studies have shown that the randomness of an STJ can be driven by a subthreshold voltage. This s...

A series of epitaxial Fe2−xTi1+xO5 (0 ≤ x ≤ 0.7) solid solution thin films was fabricated on SrTiO3 (100) substrates by pulsed laser deposition. A (230)-oriented single phase with an orthorhombic structure was obtained within a narrow growth temperature window (850–900 °C). Both the semiconducting Fe1.5Ti1.5O5 and the insulating Fe1.3Ti1.7O5, as n-...

Superparamagnetic tunnel junctions (SMTJs) are spintronic nanodevices that can oscillate spontaneously under the influence of thermal noise. Studies have proposed that SMTJs can be modeled as magnetic neurons by subjecting them to electrical Gaussian white noise and can be subsequently synchronized under subthreshold driving. Considering the non-Ga...

Spin waves (SWs) have tremendous application potential in wave-based computation utilizing a broad frequency spectrum spanning from the gigahertz to terahertz ranges. Like optical and other electromagnetic waves, SWs also promise to usher in a new era of parallel data processing with low-power consumption without Joule heating. However, this potent...

Improving our understanding of optical contributions can impact efforts to enhance the sensitivity of surface plasmon resonance (SPR) detection in the gas phase. In this study, we present a sensing strategy for amplifying detection signals by SPR planar waveguides integrated with nanoporous zeolite nanoparticles (NPs) owing to size matching between...

The fabrication of highly-ordered nanostructures by self-organization is one of the greatest challenges in nano science. Herein, we report the formation of a self-organized nanostructure in the CoGa0.8Mn1.2O4 thin film through a thermal annealing treatment. The thin film as-deposited by pulsed laser deposition exhibits a single crystalline phase ep...

Terahertz (THz) spectroscopy of solids in high magnetic fields can often provide new insight into the microscopic physics behind complex many-body behaviors [1].

We present a dynamic spin wave (SW) modulation technique using DC current to manipulate the magnetic properties of an ultralow-damping Y3Fe5O12 thin film. Microwave excitation and detection technique with two coplanar waveguide antenna arrangement on the Y3Fe5O12 (YIG) surface is used to characterize the SW. An additional platinum (Pt) stripe conne...

In this study, lutetium iron garnet (Lu3Fe5O12; LuIG) thin films have been grown on Y3Al5O12 (1 1 1) substrates by a pulsed laser deposition and are co-substituted with strong magnetically anisotropic ions of Co²⁺ and nonmagnetic ones of Si⁴⁺. LuIG is a garnet-structured ferrimagnet with an exceptionally low Gilbert damping constant as 10⁻⁵. The su...

We present a comparison of the spin wave propagation in Au/Y3Fe5O12 and Pt/Y3Fe5O12 bilayers. Microwave technique with a co-planner waveguide arrangement was used to excite and detect the spin wave. We observed a suppression in the propagating spin wave intensity when a metal stripe is placed on the surface of Y3Fe5O12 in the spin wave propagation...

The measurement and control of hydroxide ion (OH−) concentration in solution are essential in industrial processes. However, no portable sensing method directly targeting OH− ion with low-cost has been reported till date. Herein, we demonstrate an electrical detection method for OH− concentration in solution based on impedance spectroscopy of hydro...

For obtaining the changing law of electrical situations upon cell activities and conversely inducing related behaviors according to the former, a cell-based bioelectric signal sensing and stimulating system consisted of transparent oxide microelectrodes (TOEs) was demonstrated in this work. The indium tin oxide (ITO) interdigitated electrodes array...

Carrier-type control of spin-glass (cluster spin-glass) is studied in order to engineer basic magnetic semiconductor elements using the memory functions of spin-glass. A key of carrier-polarity control in magnetite is the valence engineering between Fe(II) and Fe(III) that is achieved by Ti(IV) substitution. Single phases of (001)-oriented Fe3-xTix...

CuO nanowire/microflower structure on Cu foil is synthesized by annealing a Cu(OH) 2 nanowire/CuO microflower structure at 250 °C in air. The nanowire/microflower structure with its large surface area leads to an efficient catalysis and charge transfer in glucose detection, achieving a high sensitivity of 1943 μA mM –1 cm –2 , a wide linear range u...

The effect of hydroxyl radicals (OH) and thermal annealing on an amorphous InGaZnO4 (aIGZO) film surface was investigated for manipulation of DNA immobilization. X-ray photoemission and fluorescence measurements were conducted to reveal the status of surface OH coverage and DNA immobilization, respectively. Systematic examinations concerning OH ter...

(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 resonanc...

In addition to the absorption due to known optical phonons, we found a temperature-dependent absorption band at 2 THz in garnet-type Ho3Ga5O12, at temperatures in the range of 450–540 K. The optical and electrical properties reveal that the absorption band at 2 THz is not produced by mechanisms related to soft phonons, rattling phonons, impurities,...

Epitaxial thin films of cobalt ferrite Co x Fe3− x O4 (x = 0.0, 0.5, and 1.0) were fabricated on α-Al2O3 (001) substrates using pulsed laser deposition. It was found that the coercive force of the cobalt ferrite films could be tuned by changing the Co content. The films prepared under low oxygen pressure (1.0 × 10−6 Pa) showed semiconducting behav...

We have reported on terahertz magnonics, which is a signal transmission with high-energy spin waves (electromagnons) excited by THz wave. As source and medium for electromagnons, we choose Sm3Fe5O12 ultrathin films whose magnetic properties are modified by applying an epitaxial strain. Electromagnons are successfully detected in the strained Sm3Fe5...

We report on the growth of FeO (wüstite)-based thin films using pulsed laser deposition. Epitaxial films of iron oxide with different crystal structures (corundum, spinel, and rock-salt-type) were separately fabricated by controlling the Si content in the Fe2O3-SiO2 mixture target. The rock-salt-type Fe0.92Si0.08O was found to form a solid solution...

The reststrahlen bands of rare-earth garnets were investigated in the terahertz regime. Through this, it was found that the crystal orientation and light polarization directly influence the reststrahlen-related dielectric absorptions of Gd3Ga5O12 (GGG), which is attributed to restriction in the vibrational motion of Gd ions. A theoretical fit to th...

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 t...

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 cu...

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 narrow...

Sm3Fe5O12 thin films of various thicknesses were grown on a (001)-oriented Gd3Ga5O12 substrate by pulsed laser deposition. The crystal structure of the films was strongly dependent on film thickness. The lattice was strained for thinner films due to a lattice mismatch between the film and substrate. This lattice strain was relaxed when the film thi...

The electronic structure of the oxide semiconductor ZnO has been investigated using soft x-ray angle-resolved photoemission spectroscopy (ARPES). The obtained band dispersions within the k_x-k_y planes reflect the symmetry of the Brillouin zone and show no surface-state-derived flat bands. Band dispersions along the k<sub>z</sub...