Masaki Mito

Kyushu Institute of Technology · Department of Basic Sciences

Low-temperature neutron diffraction experiments at P = 8 GPa have been conducted to investigate the magnetic structures of metallic Holmium at high pressures by employing a long d-spacing highflux diffractometer and a Paris-Edinburgh press cell inside a cryostat. We find that at P = 8 GPa and T = 5 K, no nuclear symmetry change is observed, keeping...

A prototype of the monoaxial chiral magnet CrNb3S6 exhibited two magnetostriction (MS) effects: (1) spontaneous MS due to the exchange interaction and spin-orbit coupling (SOC) at zero dc magnetic field (H) [Phys. Rev. B 102, 014446 (2020)] and (2) paramagnetic MS due to SOC and Zeeman energy at room temperature [Phys. Rev. B 105, 104412 (2022)]. C...

MnNb 3 S 6 is a monoaxial chiral magnet and stabilizes magnetic solitons in the presence of a magnetic field ( H). The number of solitons can be controlled by varying H. Furthermore, MnNb 3 S 6 exhibits magnetization relaxation due to soliton annihilation, that is, a nonequilibrium chiral soliton lattice (CSL) state. In this study, we observed soli...

Using the nanosized porous medium SBA-15, we construct the condensed spin-1 network composed of oxygen molecules (O[Formula: see text]) with tube and rod structures. The condensed network can be controlled by changing the amount of O[Formula: see text] molecules and substituting nonmagnetic nitrogen molecules (N[Formula: see text]) at the O[Formula...

[Published in Acta Materialia 236 (2022) 118117] Abstract: Despite high interest in compact and safe storage of hydrogen in the solid-state hydride form, the design of alloys that can reversibly and quickly store hydrogen at room temperature under pressures close to atmospheric pressure is a long-lasting challenge. In this study, first-principles c...

In a magnetic superlattice composed of kinks in a ferromagnetic spin array, the change in the kink number requires the movement of the kinks to and from the crystal surface. Namely, the kinks must have a velocity, and the superlattice must be nonequilibrium. Evidence of the nonequilibrium state has never been observed in previous model compounds. I...

Despite high interest in compact and safe storage of hydrogen in the solid-state hydride form, the design of alloys that can reversibly and quickly store hydrogen at room temperature under pressures close to atmospheric pressure is a long-lasting challenge. In this study, first-principles calculations are combined with experiments to develop high-e...

The intermetallic compound Fe[Formula: see text]Co[Formula: see text]Si has a helical magnetic order for [Formula: see text], whereas its orbital angular momentum contributing to the occurrence of a Dzyaloshinskii–Moriya interaction has not yet been verified. We applied soft x-ray magnetic circular dichroism spectroscopy on the Fe [Formula: see tex...

It is well known that the archetype chiral magnet MnSi stabilizes a skyrmion lattice, termed “A-phase,” in a narrow temperature range in the vicinity of the paramagnetic boundary around T c ∼ 29 K and H c ∼ 2 kOe. Recently, it has been predicted that at much lower temperatures below T c , the conical helicoid and the forced ferromagnetic (FFM) stat...

Aluminum (Al) and titanium (Ti) are superconducting materials but their superconducting transition temperatures ([Formula: see text]) are quite low as 1.20 and 0.39 K, respectively, while magnesium (Mg) never exhibits superconductivity. In this study, we explored new superconductors with higher [Formula: see text] in the Al–Mg–Ti ternary system, al...

We report that the magnetostriction (MS) effects occur in a paramagnetic state of a chiral magnet CrNb3S6. Through a series of experimental tests at room temperature, structural changes were observed at the level of a unit cell. The structural parameters are dependent of the strength and direction of magnetic field (H) even at temperature excessive...

Severe plastic deformation (SPD) is effective in producing bulk ultrafine-grained and nanostructured materials with large densities of lattice defects. This field, also known as NanoSPD, experienced a significant progress within the past two decades. Beside classic SPD methods such as high-pressure torsion, equal-channel angular pressing, accumulat...

Through advanced experimental techniques on CrI3 single crystals, we derive a pressure-temperature phase diagram. We find that Tc increases to ∼66 K with pressure up to ∼3 GPa followed by a decrease to ∼10 K at 21.2 GPa. The experimental results are reproduced by theoretical calculations based on density functional theory where electron-electron in...

A powder mixture of Al-Ti-Mg with an equal atomic fraction was subjected to severe plastic deformation using high-pressure torsion (HPT) under 6 GPa at room temperature for full consolidation. Microstructural evolution with respect to straining and annealing was examined by X-ray diffraction (XRD) analysis and high-resolution transmission electron...

Samarium (Sm) has antiferromagnetic (AFM) ordering at the hexagonal site at TN(hex)=106 K, and at the cubic site at TN(cub)=14 K at ambient pressure. The structural transition from the so-called Sm-type structure to the double hexagonal close-packed (dhcp) structure occurs at approximately 6 GPa. According to electrical resistance measurements, the...

Through advanced experimental techniques on CrI$_{3}$ single crystals, we derive a previously not discussed pressure-temperature phase diagram. We find that $T_{c}$ increases to $\sim$ 66\,K with pressure up to $\sim$ 3\,GPa followed by a decrease to $\sim$ 10\,K at 21.2\,GPa. The experimental results are reproduced by theoretical calculations base...

The monoaxial chiral magnet CrNb 3 S 6 exhibits a chiral soliton lattice (CSL) upon application of an external magnetic field (H) perpendicular to the helical axis (c-axis). The increase in the soliton (kink) number of the CSL in the process of decreasing H accompanies soliton penetration after nucleation at the surface. Avalanche soliton nucleatio...

The pressure dependence of the magnetic ordering temperatures for the lanthanide ferromagnets Gd, Tb, Dy, and Ho has been investigated in the pressure region up to 18 GPa by two types of magnetic measurements using a superconducting quantum interference device (SQUID). The present magnetic measurements enabled us to investigate the pressure depende...

We study the effects of both hydrostatic and anisotropic contractions on the molecular condensation of oxygen molecules (O2) physisorbed to nanosized pores, termed “O2 nanorods”, through the magnetization measurements. Multisteps of O2 solidification accompany the reduction in structural symmetry with decreasing temperature, such that the structura...

Previous magnetic measurements for the chiral magnet CrNb3S6 have shown that the soliton penetration and soliton dissipation in the chiral soliton lattice state strongly depend on the crystal's size and shape. We performed magnetic measurements for a thin single crystal of CrNb3S6 with a thickness 3 μm, permitting the existence of approximately 60...

The spin ice materials Ho2Ti2O7 and Dy2Ti2O7 are experimental and theoretical exemplars of highly frustrated magnetic materials. However, the effects of applied uniaxial pressure are not well studied, and here we report magnetization measurements of Ho2Ti2O7 under uniaxial pressure applied in the [001], [111], and [110] crystalline directions. The...

The coexistence of charge density wave (CDW) and superconductivity in tantalum disulfide (2H−TaS2) at low temperature is boosted by applying hydrostatic pressures to study both vibrational and magnetic transport properties. Around Pc, we observe a superconducting dome with a maximum superconducting transition temperature Tc=9.1 K. First-principles...

Despite intense efforts on all known quasi-two-dimensional superconductors, the origin and exact boundary of the electronic orderings, particularly charge density waves (CDWs), and superconductivity, are still attractive problems with several open questions. Here, in order to reveal how the superconducting gap evolves, we report on high quality com...

The coexistence of charge density wave (CDW) and superconductivity in tantalum disulfide (2H-TaS$_2$) at ambient pressure, is boosted by applying hydrostatic pressures up to 30GPa, thereby inducing a typical dome-shaped superconducting phase. The ambient pressure CDW ground state which begins at TCDW = 76 K, with critically small Fermi surfaces, wa...

We identified the spontaneous magnetostriction effects in the chiral magnet CrNb3S6 with the Dzyaloshinskii-Moriya interaction. The powdered x-ray diffraction patterns indicate a prominent magnetostriction effect at the earth field. The unit-cell volume remains almost constant, as in the so-called Invar effect, below 170 K in the paramagnetic regio...

The spin ice materials Ho2Ti2O7 and Dy2Ti2O7 are experimental and theoretical exemplars of highly frustrated magnetic materials. However, the effects of an applied uniaxial pressure are not well studied, and here we report magnetization measurements of Ho2Ti2O7 under uniaxial pressure applied in the [001], [111] and [110] crystalline directions. Th...

Hydrogen absorption and desorption through diffusive processes and the accompanying phase transformations in hydrogen storage materials have been investigated by x-ray diffraction, thermogravimetry, pressure-composition-temperature isotherms, and electrical resistance measurements. We use time- and temperature-dependent magnetic measurements to gai...

The ferromagnetic state of the spin-polarized ferromagnet La1−xSrxMnO3 is stabilized in the metallic region by strong coupling between localized spins in the t2g orbital and conduction electrons in the eg orbital. We prepared polycrystalline La1−xSrxMnO3 films (x = 0.15, 0.25, or 0.30) by deposition on an oxidized Si substrate. The three types of L...

Nd2Fe14B is a high-density Fe cluster containing 56 Fe atoms in one unit cell. We investigated the crystallographic structure of an isotropic Nd2Fe14B magnet comprising nanocrystals of a size of ~30 nm at pressures up to 2 GPa. The results of X-ray diffraction measurements using Rietveld refinement revealed the displacements of each Fe atomic site...

Nickel oxide (NiO) with bulk crystalline size is an antiferromagnetic insulator correlated strongly with crystal structure. A reduction in crystalline size causes a change in the magnetic sublattice, resulting in the appearance of ferromagnetic moments. Furthermore, in the nano crystals fabricated in mesoporous silica, there is a lattice distortion...

We have performed X-band electron spin resonance (ESR) measurements on a single crystal of the metallic chiral helimagnet CrNb3S6 from 3.5 to 180 K and for the external magnetic fields Hext, up to 4 kOe, perpendicular to the c axis (the helical axis of CrNb3S6). This field-crystalline configuration is expected to provide the chiral soliton lattice...

We examine the surface size- and shape-effects of soliton annihilation and soliton nucleation in chiral magnet CrNb3S6. We measure magnetization (M) curves of submillimeter-sized single crystals with an equal length along the c-axis (Lc = 10 μm) but with different cross sections in the ab-plane (Sab = 0.120–0.014 mm²). We find a ferromagnetic type...

In fifth-group element superconductors V, Nb, and Ta, the increase in superconducting transition temperature (Tc) was attempted by using both high-pressure torsion (HPT) and additional hydrostatic pressure (HP) compression. The former brings about the grain refinement and strain accumulation in the unit-cell level. The additional compression for se...

The chiral magnet CrNb3S6 with its solitonic objects has novel magnetic and transport properties, in which the spin-orbit coupling (SOC) plays a central role. Aiming to address the possible existence of orbital moments driven by SOC, we perform soft x-ray magnetic circular dichroism spectroscopy at the Cr L2,3 edges with in-plane magnetization. The...

We study the effects of hydrostatic pressure (HP) compression on the superconducting transition of severely strained Nb samples, whose grain sizes are reduced to the submicrometer level. Engineered granularity by high-pressure torsion (HPT) treatment changes the strength of coupling between submicrometer-scale grains and introduces lattice strain....

The high-pressure magnetic properties of the iodo-substituted bisdiselenazolyl radical ferromagnet IBPSSEt have been studied by vibrating-coil SQUID magnetometry. The magnetic state at a pressure (P) of approximately 2 GPa has the highest Curie temperature (TC) of 27.5 K, and displays an ideal three-dimensional (3D) ferromagnetic interaction networ...

In this article, uniaxial compression effects on cuprate superconductors such as YBa2Cu4O8 [Y-124], Y0.98Ca0.02Ba2Cu4O8 [Y0.98Ca0.02-124], and Hg0.83Re0.18Ba2Ca2.4Cu3.6O14 [Hg0.83(Re0.18)-1223] were reviewed. The uniaxial compression effects were compared with the hydrostatic compression effects via measuring the Meissner signal of their single cry...

We investigated transport and magnetic properties of single crystal NdFeAsO0.9F0.1 under hydrostatic pressures up to 50 GPa. The ambient pressure superconductivity at Tc∼ 45.4 K was fully suppressed at Pc∼21 GPa. Upon a further increase of pressure, ferromagnetism associated with the order of the rare-earth subsystem was induced at the border of su...

Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> nanoparticles with particle sizes of 7.8, 11.4, and 18.3 nm were synthesized in the pores of mesoporous silica, and their crystal structure...

We synthesized magnetically frustrated DyMn2O5 nanoparticles in pores of mesoporous silica, with particle sizes ranging from 7 to 20 nm, and investigated their magnetostructural correlation. We found that the lattice constants of the DyMn2O5 nanoparticles deviated from those of the bulk crystal below ∼12 nm and their crystallographic structures at...

We investigated transport and magnetic properties of NdFeAsO$_{0.9}$F$_{0.1}$ single crystal under hydrostatic pressures up to 50\,GPa. The ambient pressure superconductivity at $T_{c} \sim$ 45.4\,K is fully suppressed at $P_{c} \sim$ 21 GPa. Upon further increase of the pressure, the ferromagnetism associated with the order of rare-earth subsystem...

The magnetic properties of YBa2Cu3O7-x (YBCO) multilayered film containing BaHfO3 (BHO) nanorods at zero and small fields have been investigated. The dc magnetization and the ac susceptibility were measured with a SQUID magnetometer. The paramagnetic magnetization is shown after the field-cool-warming below the transition temperature T c = 87 K. Th...

While the layered 122 iron arsenide superconductors are highly anisotropic, unconventional, and exhibit several forms of electronic orders that coexist or compete with superconductivity in different regions of their phase diagrams, we find in the absence of iron in the structure that the superconducting characteristics of the end member BaPd 2 As 2...

The phase diagram of a cubic chiral magnet MnSi with multiple Dzyaloshinskii-Moriya (DM) vectors as a function of temperature T and dc magnetic field Hdc was investigated using intensity mapping of the odd-harmonic responses of ac magnetization (M1ω and M3ω), and the responses at phase boundaries were evaluated according to a prescription [J. Phys....

A monoaxial chiral magnet forms a kind of spin superlattice structure, termed chiral soliton lattice (CSL), by the application of a magnetic field H perpendicular to a helical chiral axis. It has been reported that the CSL accompanies the magnetoresistance effect as well as a discrete change in magnetization and magnetoresistance. In order to verif...

A chiral soliton lattice stabilized in a monoaxial chiral magnet CrNb3S6 is a magnetic superlattice consisting of magnetic kinks with a ferromagnetic background. The magnetic kinks are considered to be topological magnetic solitons (TMSs). Changes in the TMS number yield discretized responses in magnetization and electrical conductivity, and this e...

Perovskite manganite GdMnO3 nanoparticles were synthesized using mesoporous silica as a template, and their magnetic properties and crystal structure were investigated. Powder X-ray diffraction data indicated successful synthesis of the GdMnO3 nanoparticles, with mean particle sizes of 13.9 and 20.9nm. The lattice constants for the nanoparticles we...

We measured the electrical conductivity of bulk nanostructured silver prepared by high-pressure torsion (HPT) in a contactless manner by observing the AC magnetic susceptibility resulting from the eddy current, so that we could quantitatively analyze the dissipation process of the residual strain with sufficient time resolution as a function of tem...

The ceramic YBa2Cu4O8 superconductor composed of submicron grains is considered a random Josephson-coupled network containing the so-called π junctions and shows successive phase transitions. With decreasing temperature, first the intragrain superconductive transition occurs inside each grain at T c1 and then the chiral-glass transition occurs amon...

The magnetic resonance properties of microsized monoaxial chiral crystals of CrNb3S6 are investigated. We observed that the resonance of the chiral soliton lattice is sensitive to the polarization of the driving microwave field. When the microwave field is parallel to the helical axis, the resonance is symmetric with regards to the magnetic field d...

The effects of uniaxial strain and hydrostatic pressure on Hg0.83Re0.18Ba2Ca2.4Cu3.6O14[Hg0.83(Re0.18)−1223] were investigated by ac magnetic measurements under stress corresponding to a pressure of 20 GPa at maximum. According to a previous thermal study based on the Ehrenfest relation, in-plane contraction should increase the superconducting tran...

In the solid state the iodo-substituted bisdiselenazolyl radical 1c orders as a ferromagnet with TC = 10.5 K. With the application of pressure TC rises rapidly, reaching a value of 27.5 K at 2.4 GPa. The accompanying structural and magnetic changes have been examined by high resolution powder X-ray diffraction and by DFT calculations of magnetic ex...

Finding a physical approach for increasing the superconducting transition temperature (Tc) is a challenge in the field of material science. Shear strain effects on the superconductivity of rhenium were investigated using magnetic measurements, X-ray diffraction, transmission electron microscopy, and first-principles calculations. A large shear stra...

The single crystal of a chiral magnet Cr1/3 NbS 2 exhibits discrete changes in magnetization (M) in response to changes in magnetic field (H) triggered by the formation of a chiral soliton lattice (CSL). In order to provide evidence of this phenomenon, the study of the size effect is indispensable. We investigated the effects of size on this phenom...

We measured the electrical conductivity σ of aluminum specimen consisting of submicron-grains by observing the AC magnetic susceptibility resulting from the eddy current. By using a commercial platform for magnetic measurement, contactless measurement of the relative electrical conductivity σ n of a nonmagnetic metal is possible over a wide temp...

We synthesized NiO nanoparticles with particle sizes ranging from about 2 to 22 nm in the pores of mesoporous silica and investigated their crystal structure and magnetic properties. The mesoporous silica was used as a template to equalize the particle size during the fabrication of NiO nanoparticles. The NiO nanoparticles in mesoporous silica exhi...

We construct the phase diagram of the chiral magnet Cr1/3NbS2 in a dc magnetic field (Hdc) using ac magnetic susceptibility measurements. At Hdc=0, the ac response at the transition from the helical magnetic (HM) state to the paramagnetic (PM) state consists of a giant third-order harmonic component (M3ω) and a first-order harmonic component (M1ω)....

In the chiral magnet Cr1/3NbS2, discrete changes in the magnetization (M) caused by the formation of a chiral soliton lattice (CSL) were observed in magnetization curve measurements using a single crystal of submillimeter thickness. When M is measured with a minimal increment of the magnetic field H, 0.15 Oe, discrete changes in M are observed in t...

Recently, magnetic substances with chirality, namely the handedness of the magnetic structure, have attracted considerable attention because of the anomalous phenomena which appear in magnetic fields. CrNb3S6 is one of the chiral magnets formed by exchange and Dzyaloshinsky-Moriya (DM) interactions. Electron spin resonance (ESR) measurements of CrN...

We synthesized DyMn2O5 nanoparticles with the nanometer size using mesoporous silica as template of nanoparticles. The size effects of the DyMn2O5 nanoparticles were investigated through crystal structure analysis and magnetic measurement. The powder X-ray diffraction measurement revealed that the synthesized nanoparticles have orthorhombic structu...

High Tc cuprate superconducting films, such as REBa2Cu3O7-x (RE=Y, Sm, Gd), REBa2Cu4O8 (RE=Y, Yb),(Hg, Re)Ba2CaCu2O6+x, (Hg, Re)Ba2Ca2Cu3O8+x, Bi2Sr2CaCu2O8 and Bi2Sr2Ca2Cu3O10, have been studied based on “atomic level control” including lattice strain control, carrier control, and nanostructure control, in order to simultaneously improve critical...

Pressure-induced changes in the solid-state structures and transport properties of three oxobenzene-bridged bisdithiazolyl radicals 2 (R = H, F, Ph) over the range 0-15 GPa are described. All three materials experience compression of their π-stacked architecture, be it (i) 1D ABABAB π-stack (R = Ph), (ii) quasi-1D slipped π-stack (R = H), or (iii)...

The nonlinear and linear magnetic responses to an ac magnetic field H are useful for the study of the magnetic dynamics of both magnetic domains and their constituent spins. In particular, the third-harmonic magnetic response M3ω reflects the dynamics of magnetic domains. Furthermore, by considering the ac magnetic response as a function of H, we c...

We investigated the effects of hydrostatic pressure on an isotropic Nd2Fe14B magnet (the exact chemical formula is Nd2.0Fe14.1B) consisting of nanocrystals, with the size of approximately 30 nm, by magnetization measurements at pressures (P&apos;s) up to 9.3 GPa and structural analyses up to 4.3 GPa. Magnetization curves were measured by using a mi...

Hagi ware originally consists of a mixture of two raw materials: Daido clay and Mishima clay. During its firing process, we observed a change in the magnetic properties of the iron oxide, Fe2O3. The magnetic moment of the Daido clay (which only contains a small amount of the Fe2O3 γ-phase) attains a maximum at a firing temperature of approximately...

We perform structural analysis experiments on the chiral magnet Cr1∕3NbS2, in which Cr3+ ions are inserted between hexagonal NbS2 layers. The noncentrosymmetrical nature of the inserted Cr3+ appears as a distorted CrS6 octahedron. Under the application of hydrostatic pressure, the lattice shrinks significantly along the c-axis rather than the a-axi...

Self-assembly of artificial nanoscale units into superstructures is a prevalent topic in science. In biomimicry, scientists attempt to develop artificial self-assembled nanoarchitectures. However, despite extensive efforts, the preparation of nanoarchitectures with superior physical properties remains a challenge. For example, one of the major topi...

We synthesized NiO nanoparticles in the pores of mesoporous silica, with particle sizes ranging from 2.6 to 22 nm, and investigated their crystal structure and magnetic properties. The size dependence of the crystal structure exhibited a change in behavior across the critical size of 3 nm. The lattice constants attained maximal values at approximat...

We measured the temperature dependence of electrical resistivity of non-fluorine- substituted, oxygen-deficient LnFeAsO1-y (Ln = La, Ce, Nd, Tb) under hydrostatic high pressure up to '8 GPa in order to observe pressure dependence of superconducting transition temperature Tc. In LaFeAsO0.65, onset Tc initially enhances below 4 GPa, then decreases by...