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We have developed a pressure calibration method in the high-pressure THz ESR system using induction coils set outside the pressure cell. The pressure is calibrated using alternating current (AC) magnetization measurements of the superconducting transition temperature of tin set inside the pressure cell with an ESR sample. The system fits the developed pressure cell with a wide frequency range of 0.05–0.8 THz. The pressure range was extended to 2.8 GPa. The ESR system was applied to the well-known cobalt Tutton’s salt $$({\text {NH}}_{4})_{2} {\rm {Co}}({\text {SO}}_{4})_{2}\cdot {\rm {6H}}_{2} {\text {O}}$$ , and its g principal values at 0 GPa were determined as $$g_{1}=6.61$$ , $$g_{2}=3.05$$ , and $$g_{3}=2.94$$ for the first time. Furthermore, we succeeded in observing the large change in these g values with pressure.

THz electron spin resonance (ESR) measurements of the spinel compound GeCo2O4, which consists of the Co2+ pyrochlore structure, were performed. The temperature dependence measurements revealed new antiferromagnetic phases, AF1 and AF2, below TN. Moreover, a wide magnetic field range of ESR study using a single crystal at 1.8 K also revealed various field-induced phases due to the competition between the spin–lattice coupling and the spin frustration. Critical field resonances were observed at 5.0 T, 8.6 T, and 11.0 T for B//[111] and 5.1 T, 7.7 T, 11.2 T, and 13.0 T for B//[110] at 1.8 K. Although it became difficult to observe ESR above 86 K, the g-values of Co2+ ions were estimated to be g[111] = 3.34 and g[110] = 3.27 for [111] and [110], respectively, from the observed ESR mode above the saturation field at 1.8 K. Detailed frequency-field diagrams of the ESR modes at 1.8 K suggested the existence of spin–lattice coupling energy of 250 GHz (= 1.03 meV = 12 K) at the critical field resonances. The spin gap mode in the frequency-field diagram at 1.8 K showed excitation energies of E[111] = 1004 GHz (= 4.15 meV = 48 K) and E[110] = 1044 GHz (= 4.32 meV = 50 K) for [111] and [110], respectively. These results will be discussed in connection with the di-tetramer model suggested previously.

Cerium hexaboride attracts attention of solid-state community for almost 50 years. Nowadays, this material is considered as a unique example of a system with orbital ordering resulting in formation of low-temperature magnetic phase with quadrupolar order, the so-called antiferroquadrupole phase. In crystal electric field 4f 1 state of Ce3+ splits into Γ7 doublet and Γ8 quartet, the latter is believed to be the ground state, as long as just Γ8 allows quadrupolar effects. An additional tool for studying rich physics of CeB6 appeared since the discovery in this material the ESR, which is specific to antiferroquadrupole (AFQ) phase and is missing in the paramagnetic phase. In the present review, we have brought together electron spin resonance and inelastic neutron scattering data, which allowed obtaining most detailed structure of the magnetic resonance modes in the AFQ phase in a wide-frequency range up to 0.6 THz. It is shown that apart paramagnetic resonance main mode with homogeneous precession of the magnetization, there are antiferromagnetic resonance modes as well, some of them existing in the AFQ phase. Analysis of the g factors demonstrates that available theories based on Γ8 ground state are facing difficulties with accounting experimental data, thus providing a challenge for developing of a theory correctly describing dynamic magnetic properties of this interesting material.

As THz electron spin resonance (ESR) measurement has several advantages of high spectral resolution, ESR measurement beyond the zero-field splitting or the magnetic phase transition, it is a powerful means to study novel magnetic systems. Focusing on these advantages, we have been developing this THz ESR, and we are now extending to the multi-extreme THz ESR. Here the multi-extreme corresponds to the high magnetic field, the high pressure, the low temperature and the micro-mechanically detected highly sensitive THz ESR. Recent new developments and applications, especially focusing on the high pressure THz ESR, will be shown.

We systematically studied the zero-field splitting (ZFS) parameters of Fe(III) protoporphyrin IX chloride, or hemin, using the terahertz electron paramagnetic resonance (EPR) spectroscopy technique at ambient and high pressures. Although hemin is known as a model substance of hemoproteins, the pressure effect on the electronic structure has not yet been explored owing to the large ZFS. In this study, high-field and high-frequency EPR measurements were carried out in the frequency range up to 700 GHz and at hydrostatic pressures up to 2 GPa. At ambient pressure, multiple EPR branches were clearly observed, and the axial and rhombic components of ZFS were determined as $$D = 6.90\pm 0.01\hbox { cm}^{-1}$$ and $$E = 0.055 \pm 0.005\hbox { cm}^{-1}$$ , respectively. Upon pressure application, we observed a systematic shift of the resonance field, indicating a monotonous increase of the axial component from D = 6.9 to 7.9 $$\hbox {cm}^{-1}$$ at 2 GPa. The origin of this unusually large shift was discussed from a microscopic viewpoint of the electronic structure of iron under pressure.

THz electron spin resonance (ESR) measurement has been a powerful means to study novel magnetic systems because of the advantages of high spectral resolution, ESR measurement beyond the zero-field splitting or the magnetic phase transition. Therefore, we have been developing this THz ESR system since 1988, and we are now extending to the multi-extreme THz ESR. Here the multi-extreme corresponds to the high magnetic field, the high pressure, the low temperature and the micro-mechanically detected ESR. Recent new developments, especially focusing on the high pressure THz ESR, will be shown.

We present a historical review of high-pressure ESR systems with emphasis on our recent development of a high-pressure, high-field, multi-frequency ESR system. Until 2000, the X-band system was almost established using a resonator filled with dielectric materials or a combination of the anvil cell and dielectric resonators. Recent developments have shifted from that in the low-frequency region, such as X-band, to that in multi-frequency region. High-pressure, high-field, multi-frequency ESR systems are classified into two types. First are the systems that use a vector network analyzer or a quasi-optical bridge, which have high sensitivity but a limited frequency region; the second are like our system, which has a very broad frequency region covering the THz region, but lower sensitivity. We will demonstrate the usefulness of our high-pressure ESR system, in addition to its experimental limitations. We also discuss the recent progress of our system and future plans.

We performed terahertz ESR measurements of spin frustrated spinel compound GeCo2O4 using pulsed magnetic fields of up to 40 T. A very broad EPR absorption line was observed at 86 K. The g-values at 86 K were estimated to be g=5.26±0.07, 5.16±0.12 and 4.98±0.07 for B//[111], [100] and [110], respectively. High-field ESR measurements revealed complicated phase structures and a field-induced magnetic phase below 3 K. Critical fields of magnetic phases at 1.8 K for B//[111] were observed at 1.8 T, 5.0 T, 8.6 T, 11.0 T and 12.9 T for B//[111]. An energy gap of 300 GHz (=14.4 K=1.24 meV), which was related to the lattice deformation, was observed for B//[111]. The zero field gap of ω 4 mode, which is considered to be a singlet-triplet excitation of the di-tetramer, was estimated to be 1120 GHz.

The Nd-Fe-B/Mo/Fe-Co multilayered films on MgO(001) were fabricated by UHV sputtering method. The as-deposited films showed soft magnetic properties with weak perpendicular magnetic anisotropy, and after annealing above 650°C, these films showed in-plane magnetic anisotropy, good squareness, and hard magnetic properties with high coercivity of about 8 kOe. The (220) peak of Nd2Fe14B was identified in the XRD pattern after annealing of the film, which means that the c-axis, which is the easy axis of magnetization, points in the plane of the film, consistent with the measurement of the magnetization curve. The positive peak of ΔM plot of in-plane direction of the film annealed at 800°C was shown. This result suggests existence of exchange coupling between the Nd-Fe-B and Fe-Co layers in the in-plane anisotropic multilayered film with monoatomic Mo interlayer.

Due to the advantages of high spectral resolution, ESR measurement beyond the zero field splitting or the magnetic phase transition, THz electron spin resonance (ESR) measurement has been a powerful means to study novel magnetic systems. We have been developing this THz ESR system since 1988, and we are now extending to the multi-extreme THz ESR. Here the multi-extreme corresponds to the high magnetic field, the high pressure, the low temperature and the micro-mechanically detected ESR. Recent new developments, and the application of the high pressure THz ESR will be shown.

We have developed a high-pressure electron spin resonance probe and successfully installed into the world’s highest-field cryogen-free superconducting magnet having a maximum central field of 24.6 T. The high pressure of 2.5 GPa is achieved by the specially designed piston-cylinder pressure cell using THz-wave-transparent components. In the first application of this high-pressure high-field ESR system, we observed that the orthogonal dimer spin system SrCu2(BO3)2 undergoes a quantum phase transition from the dimer singlet ground to the plaquette singlet ground states.

Symmetry groups of Lie algebras and superalgebras constructed from (∈, δ)-Freudenthal-Kantor triple systems have been studied. In particular, for a special (ε, ε)-Freudenthal–Kantor triple, it is the SL(2) group. Also, the relationship between two constructions of Lie algebras from structurable algebras has been investigated.

High-field electron spin resonance measurements of perovskite compound YCrO3 powder have been performed to obtain the magnetic anisotropy. Isotropic absorption lines of electron paramagnetic resonance, which can be described as single Lorentzian shape, are observed. The g value of paramagnetic state is estimated to be 1.983 at 265 K. Magnitude of D vector of Dzyaloshinskii–Moriya interaction is estimated to be 0.36 K from Moriya’s formula using the obtained g value. Powder patterns of antiferromagnetic resonance (AFMR) with large antiferromagnetic gaps are observed below T N = 140 K. Two antiferromagnetic gaps at zero field have been estimated to be 181 GHz (6.5 T) and 338 GHz (12.1 T), and a spin flop transition field have been estimated to be 3.5 T from widely observed frequency–field diagram at 1.9 K. Although obtained AFMR modes seem to be typical AFMR modes of two sublattice antiferromagnet with triaxial magnetic anisotropy, the obtained zero-field gap is twice as large as the obtained spin flop transition field which suggests the unconventional antiferromagnetic order.

We have developed a high-pressure and multi-frequency electron spin resonance (ESR) system in the submillimeter wave region. The pressure is generated by the piston–cylinder pressure cell whose inner parts are all made of ceramics. The requirements for the inner parts of the pressure cell are toughness and transmission in the submillimeter wave region and they enable us to observe the transmitted light through a sample subjected to high pressure. It was found that both properties can be achieved by the combination of the inner parts made of the ZrO2-based ceramic and the Al2O3 ceramic. For the Shastry-Sutherland compound SrCu2(BO3)2, we observed the direct ESR transition from the singlet ground state to the first excited triplet sates at 1.5 GPa successfully in the frequency region from 300 to 700 GHz.

The S = 1/2 kagome-lattice antiferromagnet is investigated by the numerical diagonalization of 18-spin finite-size cluster. The matrix elements proportional to the intensity of the singlet--triplet electron spin resonance (ESR) transition are calculated in the presence of the Dzyaloshinsky--Moriya interaction. Some angle-dependent selection rules are also proposed. The present result would be useful to examine whether the kagome-lattice antiferromagnet has a spin gap or not, with the ESR experiment.

We have developed the high-pressure electron spin resonance (ESR) system using a micro-coil in the frequency region up to around 2 GHz and potentially 10 GHz. The hybrid-type piston-cylinder pressure cell whose maximum pressure reaches 4 GPa was used. In this study, we obtained ESR spectra at 2.3 GPa successfully, which can never be obtained by the single-layer piston-cylinder pressure cell. The minimum detectable spin number was estimated to be the order of 1012 spins/G. Moreover, it is shown that the sensitivity can be improved by two orders of magnitude using the field modulation technique. This high-pressure ESR technique is a promising one to achieve the sensitivity and the high pressure simultaneously.

YSrCrO4 is first synthesized and found to be a hettotype of the K2NiF4 structure, although the combination of Y and Sr ions in K2NiF4-type oxides is very rare. The space group of the compound is determined to be orthorhombic Pccn by the electron diffraction and the powder X-ray diffraction. Magnetic and dielectric properties of the compound, together with LaSrCrO4, YCaCrO4 and A2MnO4 (A = Sr and Ca), are investigated. YSrCrO4 shows two-dimensional (2D) spin correlations and a canted antiferromagnetic (AF) ordering. With increasing distortion of the crystal structure, 2D spin correlations and the AF transition temperature decrease, while spontaneous magnetization increases. From the multi-frequency electron spin resonance (ESR) measurements, the g-values of the paramagnetic state are estimated to be 1.976, 1.978 and 1.976 for YSrCrO4, LaSrCrO4 and YCaCrO4, respectively. Evidence of AF ordering of the Cr oxides is obtained microscopically from ESR. The dielectric measurements suggest the existence of in-gap states, while no magneto-dielectric coupling was observed in the above compounds.

Due to the advantages of high spectral resolution, ESR measurement beyond the zero field splitting or the magnetic phase transition, THz electron spin resonance (ESR) measurement has been a powerful means to study novel magnetic systems. We have been developing this THz ESR system since 1988, and we are now extending to the multi-extreme THz ESR. Here the multi-extreme corresponds to the high magnetic field, the high pressure, the low temperature and the micro-cantilever ESR. Recent new developments and the application to the study of multiferroic system will be shown.

To develop a new spin-crossover functional material, a magnetic hybrid compound [Fe(qsal)(2)][Ni(mnt)(2)] was designed and synthesized (Hqsal = N-(8-quinolyl)salicylaldimine, mnt = maleonitriledithiolate). The temperature dependence of magnetic susceptibility suggested the coexistence of the high-spin (HS) Fe(III) cation and pi-radical anion at room temperature and a magnetic transition below 100 K. The thermal variation of crystal structures revealed that strong pi-stacking interaction between the pi-ligand in the [Fe(qsal)(2)] cation and [Ni(mnt)(2)] anion induced the distortion of an Fe(III) coordination structure and the suppression of a dimerization of the [Ni(mnt)(2)] anion. Transfer integral calculations indicated that the magnetic transition below 100 K originated from a spin-singlet formation transformation in the [Ni(mnt)(2)] dimer. The magnetic relaxation of Mossbauer spectra and large thermal variation of a g-value in electron paramagnetic resonance spectra below the magnetic transition temperature implied the existence of a magnetic correlation between d-spin and pi-spin.

We introduce a notion of pre-structurable algebras based on the structurable algebra of Allison, as well as Lie algebras that satisfy triality.

Various light sources for plant production have been developed to establish a completely controlled factory. We propose a pulse light source using Xe discharge. For the rapid growth of the plant, an intense light covering the absorption spectral region of chlorophyll is demanded, and periodic irradiation is also required because the photosynthetic reaction has a certain period. In this study, Sr3MgSi2O8:Eu,Mn phosphor powders with various Eu and Mn content, which show two emission peaks in the absorption region of photosynthetic pigment and phytochrome, were synthesized, and were analyzed using X-ray diffraction, photoluminescence and electron spin resonance spectroscopy. It was found that the exchange-coupled Mn-Mn and Eu-Mn pairs lead the rapid decay of Mn emission and efficient energy transfer from Eu and Mn ions, respectively. A plasma tube array panel using the phosphor was also fabricated and the similar emission spectrum of Sr3MgSi2O8:Eu,Mn is obtained under vacuum-UV excitation in comparison to the UV excitation.

We have developed a high-field and high-frequency ESR system using a commercially available magnetometer equipped with the superconducting quantum interference device (SQUID). This is magnetization detection type ESR and ESR is observed as a change of the magnetization at the resonance condition under irradiation of the electromagnetic wave. The frequency range is from 70 to 315 GHz and the maximum magnetic field is 5 T. The sensitivity is estimated to be 10 13 spins/G. The advantage of this system is that the high-field ESR measurements can be made very easily and quantitatively. Moreover, this high-field ESR can be applied to the measurements under pressure by using a widely used piston-cylinder pressure cell.

A hybrid-type piston-cylinder pressure cell for the electron spin resonance (ESR) measurement has been developed. The cylinder of this pressure cell consists of a NiCrAl inner cylinder and a CuBe outer sleeve, and all inner parts are made of zirconium oxide which has good transmittance to the millimeter and submillimeter waves. We confirmed that the pressure reaches 2.1 GPa. We have also developed a transmission-type high-field ESR system having two different modulation methods for this pressure cell. A test measurement without pressure cell for the two-dimensional orthogonal-dimer spin system of SrCu2(BO3)2 has been done successfully in the wide frequency region. The combination of this electromagnetic wave transmission-type pressure cell and this high-field ESR system is a promising tool for the study of the pressure-induced phase transition of SrCu2(BO3)2.

Recent developments of “multi-extreme” high magnetic field electron spin resonance (ESR) in Kobe will be reviewed. Our high magnetic field ESR covers the frequency region between 0.03 and 7 THz and the temperature region between 1.8 and 300 K. With this high magnetic field ESR system we can apply the magnetic field up to 55 T using a Cu-Ag pulsed magnet and a 300 kJ (10 kV) capacitor bank. Under this high magnetic field we can also apply the high pressure up to 1.4 GPa. As we can make the measurement under low temperature, high magnetic field and high pressure simultaneously, we name it as “multi-extreme” ESR. Moreover, in order to gain the sensitivity of our high magnetic field ESR, we have developed a micro-cantilever ESR system using a torque method, which enables the ESR measurement of micrometer size single crystal at low temperature. At the moment we are in the process of extending the magnetic field region of micro-cantilever ESR. Recently we have succeeded in making the measurement up to 369 GHz and the achieved sensitivity is about 1010 spins/G, which is much higher than that using the conventional transmission method. Finally our development of magnetization detected ESR using SQUID magnetometer (SQUID ESR) will be also presented.

We study Lie algebras endowed with an action by automorphisms of the dicyclic group of degree 3. The close connections of these algebras with Lie algebras graded over the non-reduced root system BC1, with J-ternary algebras and with Freudenthal–Kantor triple systems are explored.

We perform photoluminescence measurement of GaAs:Er,O under a pulsed magnetic field up to 60 T and succeed to obtain the magnetic field dependence of three main photoluminescence peaks. We also estimate the energy splitting of states 4I15/2 and 4I13/2 using the crystal field theory. Theoretically calculated energy differences between the lowest state of J= 13 2 and the lowest three states of J= 15 2 are in good agreement with experimentally obtained energy of three main PL peaks. We discuss the local configuration around the luminescent Er-2O center. By using parameters in the crystal field calculation, our analysis suggest that not only O2− sites but also As3− sites adjacent to Er3+ ion are displaced from their original lattice positions.

In this paper, we discuss a connection between (−1, −1)-Freudenthal–Kantor triple systems, anti-structurable algebras, quasi anti-flexible algebras and give examples of such structures. The paper provides the correspondence and characterization of a bilinear product corresponding a triple product.

High-frequency electron spin resonance (ESR) measurements of S = 1/2 one-dimensional Heisenberg antiferromagnetic zig-zag chain substance (VO)(SO4)(2,2-bpy) were performed in the temperature region from 1.8 to 265 K. ESR measurements at 265 K show typical powder pattern spectra of the V4+ ion and g || = 1.925 ± 0.001 and g ⊥ = 1.976 ± 0.001 were obtained. Although the magnetic susceptibility shows a maximum at 3.1 K suggesting the existence of a short-range order, no g-shift and line width broadening were observed down to 1.8 K. We suggest that these temperature-independent features of ESR can be attributed to the result of frustration in (VO)(SO4)(2,2-bpy).

In this paper we give a review on $\delta$-structurable algebras. A connection between Malcev algebras and a generalization of $\delta$-structurable algebras is also given.

A series of deposits recording the early Holocene drastic changes in coastal environment was investigated in terms of sedimentology and paleontology at the Okinoshima archeological site on the southwest coast of Boso Peninsula, central Japan. The deposits, ca. 3 m thick exposed in trenches, consist of structureless mud and overlying stratified sand, divided into three units, I, II, and III in ascending order. Unit I is poorly sorted sandy mud with abundant opal phytoliths. Unit II, gradually overlying unit I, is poorly sorted sandy mud containing more organic material and pieces of wood, and archeological remains. Unit III overlies unit II with a sharp erosional contact and is composed of well-sorted medium-grained sand intercalated by mud layers with abundant plant fossils. Unit I suggests a dry surface on a coastal plain near uplands. Unit II was transported from the upland onto the coastal plain by a debris flow. Unit III deposits resulted from high-energy river and storm surge flows onto the coastal plain. The succession records that the sedimentary environments of the study site changed successively from a slope near the uplands, to a fluvial plain, to a coastal plain in response to a sea-level rise in the early Holocene. AMS ages of the units are approximately 10,000 cal BP, and deposition occurred within 1000 years.

For the sensor probe of high frequency magnetic field in GHz region, films were prepared by liquid phase epitaxy technique and ferromagnetic resonances were investigated in high frequency region. Magneto-optical (MO) effect of magnetic garnet was utilized for the imaging sensor of the magnetic field distribution. However, for the application to the characterization of high frequency magnetic field in the GHz frequency region, usual MO measurements are difficult to detect the magnetic filed as the decreasing of the permeability of magnetic garnet. Magnetic resonance is an effective way to induce magnetic moment and enhance the magnetooptical effect in high frequency region of GHz order. In order to understand the possibility of magnetic field sensor of high frequency in detail, far-infrared magnetic resonances were measured at the high frequencies up to 315 GHz in pulsed high magnetic field. Taking account into sensitivity of MO signals and magnetic resonance intensities, magnetooptical method using a garnet film is effective at the frequencies below 100 GHz.

High-pressure and high-field electron spin resonance (ESR) measurements have been performed on a single crystal of the orthogonal-dimer spin system SrCu$_{2}$(BO$_{3}$)$_{2}$. With frequencies below 1 THz, ESR signals associated with transitions from the singlet ground state to the one-triplet excited states and the two-triplet bound state were observed at pressures up to 2.1 GPa. We obtained directly the pressure dependence of the gap energies, finding a clear first-order phase transition at $P_{c}=1.85\pm0.05$ GPa. By comparing this pressure dependence with the calculated excitation energies obtained from an exact diagonalization, we determined the precise pressure dependence for inter- ($J'$) and intra-dimer ($J$) exchange interactions considering the Dzyaloshinski-Moriya interaction. Thus this system undergoes a first-order quantum phase transition from the dimer singlet phase to a plaquette singlet phase above the ratio $(J'/J)_{c}=0.660\pm0.003$.

S=1/2 one-dimensional chain and dimer system Cu3Mo2O9, in which the super-exchange network forms one-dimensional corner-sharing tetrahedoron of Cu2+ ion, has been investigated by high field ESR measurements using the powder sample and the pulsed magnetic field up to 40 T at 2.0 K. The high field ESR measurements with wide frequency range suggest the existence of the magnetic phase transition at 8 T. Three ESR modes appear above 18 T, which corresponds to the magnetization jump. The ground state of Cu3Mo2O9 will be discuss.