Search

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.

In solid-state physics, pressure is an essential parameter, which can continuously change the interaction between electrons. The combination of terahertz electron spin resonance (THz ESR) with pressure is a powerful approach to clarify the spin state under pressure from the microscopic point of view, especially for quantum magnets. The most important feature of our high-pressure THz ESR system is that our pressure cell ensures the high pressure and wide frequency range using ceramics in internal parts, which are well balanced in terms of toughness and transmittance of electromagnetic waves. This approach allowed to very accurately describe the spin state under pressure. In this review, high-pressure ESR systems are reviewed with a focus on those in the high-frequency region. In addition, we show differences between other systems and our system. Moreover, we show the usefulness of our system by showing application examples of several magnetic materials of interest.

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.

A porphyrin analogue embedded with (S)-1,1&prime, bi-2-naphthol units was synthesized without reducing optical purity of the original binaphthol unit. This new macrocyclic ligand provides the hexaanionic N4O4 coordination environment that enables a linear array of three metal ions. That is, it provides the square planar O4 donor set for the central metal site and the distorted square planar N2O2 donor set for the terminal metal sites. In fact, a CuII3 complex with a Cu(1)&ndash, Cu(2) distance of 2.910 &Aring, a Cu(1)&ndash, Cu(2)&ndash, Cu(1&prime, ) angle of 174.7&deg, and a very planar Cu2O2 diamond core was obtained. The variable-temperature 1H-NMR study of the CuII3 complex showed increasing paramagnetic shifts for the naphthyl protons as temperature increased, which suggests strong antiferromagnetic coupling of CuII ions. The temperature dependence of the magnetic susceptibility indicated antiferromagnetic coupling both for the CuII3 complex (J = &minus, 434 cm&minus, 1) and for the NiII3 complex (J = &minus, 49 cm&minus, 1). The linear (L)M(&micro, OR)2M(&micro, OR)2M(L) core in a rigid macrocycle cavity made of aromatic components provides robust metal complexes that undergo reversible ligation at the apical sites of the central metal.

Salts of cationic sandwich complexes often exhibit an ionic plastic phase; however, only a few exhibit a plastic phase at room temperature. To explore the use of the CF3BF3 anion to lower the transition temperature to the plastic phase, we prepared salts of CF3BF3 with various ferrocene derivatives, [D][CF3BF3] (D=FeCp*(2), Fe(C5Me4H)(2), Fe(C5H4Me)(2), FeCp(C5H4Me), FeCp2; Cp*=C5Me5, Cp=C5H5). Although [FeCp*(2)][CF3BF3] exhibited a plastic phase above 417 K, the other salts formed room-temperature ionic plastic crystals with a phase transition to the plastic phase in the range 266-291 K. The crystal structure and thermal properties of [FeCp2][OTf] were elucidated for comparison. In addition, decamethylferrocenium salts with other anions were synthesized and structurally characterized: [FeCp*(2)][X] (X=N(SO2F)(2) and B(CN)(4)) exhibited a phase transition to the plastic phase above 400 K, whereas carborane-containing salts [FeCp*(2)](2)[B12F12] and [FeCp*(2)][Co(C2B9H11)(2)] did not exhibit a plastic phase.

We report the thermally detected electron spin resonance (ESR) spectroscopy in the frequency range of millimeter and submillimeter waves. Under high vacuum conditions, a cantilever-shaped device detects ESR absorption of a mounted sample as a temperature difference in its beam direction. Despite the simple experimental setup, the spin sensitivity of the order of 10(12) spins/G was achieved at 10 K. The developed sample stage is small enough to be used in a 10 T split-pair superconducting magnet with a bore of 25 mm, enabling precise field-angle-dependent ESR measurements at multi-frequencies above 500 GHz. We demonstrate its usefulness by studying the field-angle dependence of the excitation energy of the dimer triplet state in the Shastry–Sutherland magnet SrCu2(BO3)2.

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 report the discovery of a first-order phase transition at around 125 K in NbCrP, which is a nonsymmorphic crystal with Pnma space group. From the resistivity, magnetic susceptibility, and nuclear magnetic resonance measurements using the crystals made by the Sn-flux method, the high-temperature (HT) phase is characterized to be metallic with a non-negligible magnetic anisotropy. The low-temperature (LT) phase is also found to be a nonmagnetic metallic state with a crystal of lower symmetry. In the LT phase, the spin susceptibility is reduced by ~30 % from that in the HT phase, suggesting that the phase transition is triggered by the electronic instability. The possible origin of the phase transition in NbCrP is discussed based on the electronic structure by comparing with those in other nonsymmorphic compounds RuP and RuAs., Comment: 9 pages, 9 Postscript figures

The relationship between the valence states of Eu ions in Eu-doped GaN and their magnetic properties is investigated by experiments and simulations. X-ray measurements have verified that the valence states of Eu ions can be controlled through growth temperature and codopants and that the highest concentration of divalent Eu ions is found in samples grown at 700 ° C by codoping with Si and O. According to our phenomenological analysis, magnetoresistance measurement implies the presence of Zener’s p–f exchange interaction. However, the magnetization dependence on an external magnetic field shows non-hysteretic sigmoidal curves in all the samples. Our simulations suggest that this is due to the formation of nanostructures of the magnetic impurities in the samples by spinodal decomposition.The relationship between the valence states of Eu ions in Eu-doped GaN and their magnetic properties is investigated by experiments and simulations. X-ray measurements have verified that the valence states of Eu ions can be controlled through growth temperature and codopants and that the highest concentration of divalent Eu ions is found in samples grown at 700 ° C by codoping with Si and O. According to our phenomenological analysis, magnetoresistance measurement implies the presence of Zener’s p–f exchange interaction. However, the magnetization dependence on an external magnetic field shows non-hysteretic sigmoidal curves in all the samples. Our simulations suggest that this is due to the formation of nanostructures of the magnetic impurities in the samples by spinodal decomposition.

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.

We experimentally studied the pressure dependence of the zero-field splitting (ZFS) parameter of hemin (iron(III) protoporphyrin IX chloride), which is a model complex of hemoproteins, via high-frequency and high-field electron paramagnetic resonance (HFEPR) under pressure. Owing to the large ZFS, the pressure effect on the electronic structure of iron-porphyrin complexes has not yet been explored using EPR. Therefore, we systematically studied this effect using our newly developed sub-terahertz EPR spectroscopy system in the frequency range of 80-515 GHz, under magnetic fields up to 10 T and pressure up to 2 GPa. We observed a systematic shift of the resonance fields of hemin upon pressure application, from which the axial component of the ZFS parameter was found to increase from D = 6.9 to 7.9 cm-1 at 2 GPa. In contrast to the previous methods used to study proteins under pressure, which mainly focused on conformational changes, our HFEPR technique can obtain more microscopic insights into the electronic structures of metal ions under pressure. In this sense, our technique provides novel opportunities to study the pressure effects on biofunctional active centers of versatile metalloproteins.

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.

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.

To introduce both an inter-sulphur atom and π-stacking interaction between a spin crossover (SCO) cation and paramagnetic anion, we designed and synthesised two novel Fe(II) SCO compounds involving a terpyridine-type thiazole containing ligand with the paramagnetic Ni(dmit)2 and nonmagnetic Au(dmit)2 anion (dmit = 4,5-dithiolato-1,3-dithiole-2-thione). The temperature variations of magnetic susceptibility and Mossbauer spectroscopy revealed that both complexes exhibited an almost complete SCO conversion, and moreover, the Ni(dmit)2 anion was in a paramagnetic state down to 2 K. The crystal structures for the Ni(dmit)2 complex at 213 and 400 K indicated that the chalcogen-bond and π-stacking interaction would be enhanced by the electrostatic interaction between the cation and anion, preventing the π-radicals from dimerising. The light-induced excited spin state trapping effect was observed at 5 K.

We have developed special XLPE material (DC-XLPE) suitable for DC insulation. It was optimized for well-control of space charge. Basic properties of the material and reliability of cable system were evaluated in numbers of measurements and test programs. Higher volume resistivity, controlled behavior of space charge even in case of polarity reversal and excellent long term performance of DC-XLPE were confirmed by measurements of sheet samples. Higher capability of system performance including combinations of cable and accessories was also confirmed by tests using model cable system. Finally, 320kV full size DC cable system was tested in accordance with prequalification test program of CIGRE TB-496. It was completed successfully. After that, a part of test loop was dismantled for space charge measurement. Space charge behavior was still well-controlled even after 1 year-long test.

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.

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.

Highly oriented pyrolytic graphite (HOPG) samples were irradiated by highly charged ions Ar11+ and Xe26+. Scanning electron microscopy (SEM), electron spin resonance (ESR), a superconducting quantum interference device (SQUID), and Raman spectroscopy were used to investigate the effect of this irradiation. SEM observations revealed that the contrast between irradiated and unirradiated regions became discernible at a fluence of about 1014cm -2. On the other hand, for samples irradiated by Ar+ ions, a fluence of the order of 1015cm -2 was necessary to obtain a similar contrast to that obtained by Ar11+ ion irradiation. This demonstrates that highly charged ions effectively enhance modification of solid surfaces. Furthermore, the ESR and SQUID measurements revealed the formation of defects and magnetization of the irradiated surface. Raman measurements were also performed to investigate the structural transformation at different fluences. © 2011 The Surface Science Society of Japan.

We performed 75As nuclear quadrupole resonance (NQR) measurements on single-crystalline Ru1−xRhxAs to study the relationship between the superconductivity observed in a limited Rh-substitution regi...

The single crystal of RuAs obtained by Bi-flux method shows obvious successive metal-insulator transitions at T_MI1~255 K and T_MI2~195$ K. The X-ray diffraction measurement reveals a formation of superlattice of 3x3x3 of the original unit cell below T_MI2, accompanied by a change of the crystal system from the orthorhombic structure to the monoclinic one. Simple dimerization of the Ru ions is nor seen in the ground state. The multiple As sites observed in nuclear quadrupole resonance (NQR) spectrum also demonstrate the formation of the superlattice in the ground state, which is clarified to be nonmagnetic. The divergence in 1/T_1 at T_MI1 shows that a symmetry lowering by the metal-insulator transition is accompanied by strong critical fluctuations of some degrees of freedom. Using the structural parameters in the insulating state, the first principle calculation reproduces successfully the reasonable size of nuclear quadrupole frequencies for the multiple As sites, ensuring the high validity of the structural parameters. The calculation also gives a remarkable suppression in the density of states (DOS) near the Fermi level, although the gap opening is insufficient. A coupled modulation of the calculated Ru d electron numbers and the crystal structure proposes a formation of charge density wave (CDW) in RuAs. Some lacking factors remain, but it shows that a lifting of degeneracy protected by the non-symmorphic symmetry through the superlattice formation is a key ingredient for the metal-insulator transition in RuAs., Comment: 10 pages, 10 figures

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 $(J'/J)_{c}=0.660\pm0.003$.

Development of multi-extreme electron spin resonance (ESR) measurement system is in progress in Kobe. We have installed the pulsed magnetic field up to 55 T and our high field ESR system can cover the frequency region from 30 GHz to 7 THz. Our aim is to extend our high field ESR system to the multi-extreme ESR measurement system by combining low temperature, high pressure and nano techniques, and the combination with the high pressure is focused in the paper. High pressure can be achieved up to 1.4 GPa by using the transmission type piston cylinder pressure cell. We have succeeded in combining the high field and the high pressure. As an example, the pressure dependence of the spin gap in SrCu2(BO3)2, S=1/2 Shustally-Sutherland dimer system, observed by our multi-extreme ESR measurement is presented. This measurement is the direct and precise measurement of the spin gap, and the spin gap decreased from 723 GHz (34.7 K) to 581 GHz (27.9 K) at 1.2 GPa.

We have made a survey of ceramics for the inner parts of the transmission-type pressure cell to achieve the high pressure and the high transmission in THz range. By using the optimal combination of ZrO$_{2}$-based ceramic and Al$_{2}$O$_{3}$ ceramic, we have succeeded in obtaining the pressure up to 1.5 GPa and the frequency region up to 700 GHz simultaneously. We show the high-pressure ESR results of Shastry-Sutherland compound SrCu$_{2}$(BO$_{3}$)$_{2}$ as an application. We observed the direct ESR transition modes between the singlet ground state and the triplet excited states up to the pressure of 1.51 GPa successfully, and obtained the precise pressure dependence of the gap energy. The gap energy is directly proved to be suppressed by the pressure. Moreover, we found that the system approaches the quantum critical point with pressure by comparing the obtained data with the theory. This result also shows the usefulness of high-pressure ESR measurement in THz region to study quantum spin systems.

Recently, a new tetragonal compound CeRu2Al2B, which shows successive magnetic transitions of antiferromagnetic and ferromagnetic orders was discovered. In this paper, the results of magnetization measurements on magnetically-aligned powder sample of CeRu2Al2B were reported. Highly-anisotropic behaviors between the magnetizations along the easy and the hard directions were observed. The anisotropic behavior of the magnetizations could be explained qualitatively by considering the crystalline-electric-field scheme with the Γ7(1) doublet ground state estimated from the previous nuclear magnetic resonance experiments. These results support the Ising-type ferromagnetic structure along the c-axis.

High-field ESR technique has been applied to the novel frustrated spin chain system KCu5V3O13, to reveal the peculiar ground state proposed by the previous results of the magnetic susceptibility and the magnetization measurements. We successfully observed the antiferromagnetic resonance with the easy axis type anisotropy below 7 K . In addition, small shifts of the resonance field probably due to the re-arrangements of spin configuration in the ordered phase were also observed at about 4 K in the detailed temperature dependence measurements. This result confirmed the observation of double peaks at 3.9 and 7 K in the specific heat measurements performed in advance to the high-field ESR measurements. We will discuss about the ground state of KCu5V3O13 based on these results together with those obtained in the KMgCu4V3O13, where no antiferromagnetic resonance was observed.

High-field ESR measurements of S= 1 2 triangular antiferromagnet CsCuCl3 have been performed at 6 K under pressure using the pulsed magnetic field up to 16 T in the frequency region from 120 to 360 GHz . We found that both the phase transition field and the antiferromagnetic gap increased under pressure. The origin of the increase of the antiferromagnetic gap was concluded to be due to the increase of the easy-plane type anisotropy as well as the increase of the interchain interaction of this system. The increase of the easy-plane type anisotropy was consistent with the increase of the phase transition field under pressure as suggested by Nikuni and Shiba's theory.

We have developed a low-temperature ESR system under pressure, which has the frequency region above 70 GHz, the pulsed magnetic field up to 16 T and the pressure region up to about 3.5 kbar. A suitable pressure-calibration method using the change of the ESR of ruby under pressure has been also developed. We can determine the pressure and observe ESR signals of a sample at the same time. The high-field ESR measurements with the pulsed magnetic field up to 16 T have been performed on triangular antiferromagnet CsCuCl 3 for H||c around 6 K at 1 bar and at 3.1 ± 0.6 kbar in the frequency region from 120 GHz to 370 GHz. We observed the increase of the phase transition field from the umbrella-type configuration to the coplanar configuration due to the quantum fluctuation and the increase of the antiferromagnetic gap under pressure. The possible origin of this increase of the phase transition field was discussed in connection with the recent magnetization measurements under pressure.

Magnetization, specific heat, and electrical resistivity measurements have been performed on polycrystalline samples of a new cubic compound, Ce6Pd13Zn4. This compound exhibits metallic behavior and is classified as a Kondo-lattice system. The trivalent Ce ions are responsible for the antiferromagnetic transition at TN = 3.3 K and the phase transition at \(T'_{\text{N}} = 1.3\) K with the formation of superzone gaps. The increase in magnetic susceptibilities below TN and the considerably large value of the specific heat divided by temperature (1.25 J·Ce-mol−1·K−2) imply the existence of non-ordered Ce magnetic moments due to the geometrical frustration on the octahedral Ce sublattice.

The microscopic magnetic properties of high-quality GdN thin films have been investigated by electron spin resonance (ESR) and ferromagnetic resonance (FMR) measurements. Detailed temperature dependence ESR measurements have shown the existence of two ferromagnetic components at lower temperatures, which was not clear from the previous magnetization measurements. The temperature, where the resonance shift occurs for the major ferromagnetic component, seems to be consistent with the Curie temperature obtained from the previous magnetization measurement. On the other hand, the divergence of line width is observed around 57 K for the minor ferromagnetic component. The magnetic anisotropies of GdN thin films have been obtained by the analysis of FMR angular dependence observed at 4.2 K. Combining the X-ray diffraction results, the correlation between the magnetic anisotropies and the lattice constants is discussed.

In a frustrated J_1-J_2 chain with the nearest-neighbor ferromagnetic interaction J_1 and the next-nearest-neighbor antiferromagnetic interaction J_2, novel magnetic states such as a spin-nematic state are theoretically expected. However, they have been rarely examined in experiments because of the difficulty in obtaining suitable model compounds. We show here that the quasi-one-dimensional antiferromagnet NaCuMoO_4(OH), which comprises edge-sharing CuO_2 chains, is a good candidate J_1-J_2 chain antiferromagnet. The exchange interactions are estimated as J_1 = - 51 K and J_2 = 36 K by comparing the magnetic susceptibility, heat capacity, and magnetization data with the data obtained using calculations by the exact diagonalization method. High-field magnetization measurements at 1.3 K show a saturation above 26 T with little evidence of a spin nematic state expected just below the saturation field, which is probably due to smearing effects caused by thermal fluctuations and the polycrystalline nature of the sample., 6 pages, 4 figures

Polycrystalline and single crystalline samples of La-substituted compounds of CeRu2Al2B were grown and their magnetization and electrical resistivity were measured to examine the origins of high transition temperatures and a complex magnetic structure. A ferromagnetic(FM) and an antiferromagnetic-transition temperatures decrease linearly with increasing La concentration, which implies that the high transition temperatures are not ascribable to a quadrupolar interaction but a characteristic band structure. A competition of some kinds of magnetic interactions may be responsible for the appearance of a complex magnetic structure.

X-band and millimeter wave ESR measurements have been performed on (DI-DCNQI) 2 Ag single crystals. X-band ESR measurements were carried out with the static magnetic field up to 1 T. Electron param...

Recent development of the high-field facility in Kobe University is presented. We installed a 3 kV, 100 kJ capacitor bank, this is four times larger in energy than the previous one, and we achieved 42 T recently using a Cu–Ag pulsed magnet. Recent high-field ESR studies of quantum spin systems such as high pressure phase (VO)2P2O7 will be presented. The high-pressure phase of (VO)2P2O7 is the S= 1 2 bond alternating antiferromagnet; we found an anomaly in the ESR mode of the high-pressure phase (VO)2P2O7 single crystal at 20 T by observing the frequency dependence at 4.2 K. Finally, we refer to our new development of the high-field ESR system under high pressure. We developed a compact pressure cell with sapphire window which fits into our pulsed magnet. The ESR result using this pressure cell will be presented.

We studied the ferromagnetic phase transition and the resultant change in the optical band gap of GdN thin films grown by a reactive sputtering technique in an ultra-high vacuum process. The GdN thin film exhibited two phases of spin ordering; the short correlation of spins starts to develop below ∼60 K, and the long-range ferromagnetic ordering emerges below the Curie temperature of 37 K. GdN has been confirmed to be an indirect band gap semiconductor. We found that the band-gap is dramatically reduced with the ferromagnetic spin ordering. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Segmented polyurethane dispersions (SPUD) having carboxyl groups in soft segments (SS) or hard segments (HS) were synthesized. Phase, surface, and interface structures of films made from those SPUD were examined by differential scanning calorimeter (DSC), contact angle, and X-ray photoelectron spectroscopy (XPS) measurements. Segmented polyurethanes (SPU) with the same structures as SPUD were also synthesized in the organic solvent system, and the properties and behaviors of these SPU films were compared with the SPUD films. It was indicated by the DSC measurements that the film made from SPUD having carboxyl groups in the soft segments (S-SPUD) had higher crystallinity and crystal growth rate than the film made from SPUD having carboxyl groups in the hard segments (H-SPUD) in spite of steric hindrance. On the other hand, the film made from SPU having carboxyl groups in the hard segments (H-SPU) had higher crystallinity than the film made from SPU having carboxyl groups in the soft segments (S-SPU). Further, the crystal growth rate of SPU was faster than that of SPUD, regardless of the position of carboxyl groups. These results indicated that the phase structure of SPUD film was affected by the phase structure in the dispersion particle. Surface and interface structure of SPUD film was rearranged with a change of the phase structure. But the degree of this change was higher in the surface structure than in the interface structure. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 741–748, 1999

X-band ESR measurements have been performed on Na 0.5 CoO 2 in the temperature region between 4.5 K and room temperature. The anisotropic g values were observed at room temperature. A large g shift and an increase of the linewidth were also observed as temperature was decreased above T c 1 = 87 K . In addition, no clear signal was observed below T c 1 in a range of the measured magnetic field and this behavior supports the long range antiferromagnetic order at T c 1 . The origin of the large g shift with decreasing temperature will be discussed.

High field ESR measurements have been performed on newly synthesized layered manganese oxides A 4 Mn 3 O 10 (A=Ba, Sr) using a pulsed magnetic field up to 16 T. From the temperature and the frequency dependence measurements, it was confirmed that both ground states at low temperature are the antiferromagnetic ordered state. The typical AFMR absorption lines were observed for both compounds and both were well explained by the AFMR theory for a two-sublattice antiferromagnet with orthorhombic magnetic anisotropy. Moreover, we found that the magnetic anisotropy energies in these compounds are very small as compared with their exchange interactions.

Multi-extreme THz ESR measurements have been performed on Cr-jarosite, which is an ideal model substance of highly frustrated kagome antiferromagnet. The analysis of antiferromagnetic resonances observed at 1.9K revealed the Dzyaloshinsky-Moriya interaction, which plays an important role on the ground state.

AlN/GdN/AlN double heterostructures were grown on c-sapphire substrates using a reactive rf sputtering method under high vacuum conditions. The optical absorption spectrum of the GdN shows a clear fundamental band edge of GdN around 800 nm; this transition is attributed to the minority spin band energy of GdN at the X point. Nitrogen vacancy centers cause a blue-shift of the optical band edge of GdN, which could be ascribed to both the band filling, and the electron-hole interactions resulting from the free carriers generated by nitrogen vacancies. Temperature-dependent magnetization measurements demonstrate a clear change in the magnetization values of GdN with respect to the N2 partial pressure. Nitrogen vacancy centers in the thin GdN film raise the Curie temperature from 31 K to 39 K, which has been accurately measured by the Arrott plots.

We report the synthesis and the magnetic susceptibility of (pipdH)2Cu1-xZnxBr4, which is a nonmagnetic impurity-doped S=1/2 spin ladder system. The samples were synthesized from a solution by using a slow evaporation method. Samples were confirmed to be in a single phase and to have the same crystal structure as the pure system (pipdH)2CuBr4 by using X-ray diffraction measurements. To check the magnetic properties, we performed magnetic susceptibility and magnetization measurements with a SQUID magnetometer. A plot of the inverse magnetic susceptibility indicates the presence of dominant antiferromagnetic coupling. The magnetic susceptibility shows a broad maximum due to low dimensionality and a spin gap behavior related to the two-leg spin ladder at low temperature. The spin gap and the Curie constants of Zn-doped samples, as estimated from an analysis of the magnetic susceptibility, monotonically decrease as the Zn concentration decreases. A nonmagnetic impurity of S=1/2 spin ladder system affects the spin gap., Comment: 12 pages, 5 figures

Many efforts are under way to control the structure of heterointerfaces in nanostructured composite materials for designing functionality and engineering application. However, the fabrication of high-quality heterointerfaces is challenging because the crystal/crystal interface is usually the most defective part of the nanocomposite materials. In this work, we show that fully dense insulator (MgO)/semiconductor(Mg2Si)/superconductor(MgB2) nanocomposites with atomically smooth and continuous interfaces, including epitaxial-like MgO/Mg2Si interfaces, are obtained by solid phase reaction between metallic magnesium and a borosilicate glass. The resulting nanocomposites exhibit a semiconductor-superconducting transition at 36 K owing to the MgB2 nanograins surrounded by the MgO/Mg2Si matrix. This transition is followed by the intergrain phase-lock transition at ∼24 K due to the construction of Josephson-coupled network, eventually leading to a near-zero resistance state at 17 K. The method not only provides a s...