Shigeki Nimori - Academia.edu (original) (raw)

Papers by Shigeki Nimori

Solid State Communications, Sep 1, 2003

Using single crystals of Bi 2 Sr 2 CaCu 2 O 8 , a detailed study for the thermoremanent magnetiza... more Using single crystals of Bi 2 Sr 2 CaCu 2 O 8 , a detailed study for the thermoremanent magnetization (TRM) was performed at low AC applied field in the low temperature region ð5 # T # 20 KÞ: Below approximately 20 K, the AC susceptibility of TRM shows anomalous dispersion response with large amplitude. The origin of the unstable response has been discussed in relation with the pinning force.

Journal of the Physical Society of Japan, Jul 15, 1998

La (P1) and apical oxygen (P2) vibrations along the c-axis, which are A1g-symmetry in the tetrago... more La (P1) and apical oxygen (P2) vibrations along the c-axis, which are A1g-symmetry in the tetragonal phase (I4/mmm), have been systematically investigated for K2NiF4-type oxide superconductors; La2CuO4+delta (delta=0, 0.014, 0.063), La1.85Sr0.15CuO4, and Sr2RuO4. For La2CuO4+delta, with increasing of the excess oxygen concentration (delta), the intensity of P2 decreases exponentially as a function of delta at room temperature.This decrease can be

IEEE Transactions on Applied Superconductivity, Jun 1, 2006

ABSTRACT

Physical review, Mar 20, 2001

Physical review, Mar 15, 2001

We have systematically investigated the totally symmetric Raman-scattering spectra of Sr 2 RuO 4 ... more We have systematically investigated the totally symmetric Raman-scattering spectra of Sr 2 RuO 4 crystals in the temperature region between room temperature and 6 K. The electron-phonon interaction for the apical oxygen vibration has been experimentally investigated by a line-shape analysis based on the Fano interference model. It has been found that the electron-phonon interaction strongly depends on not only the polarization geometry but also the phonon-propagating direction. The phonon, which travels along the RuO 2 plane in the (a,a) geometry, shows the strongest electron-phonon interaction. The intensity of the broad background due to the magnetic excitation has been suppressed in the energy region less than 300 cm Ϫ1 at low temperature. Furthermore, the anisotropic formation of the spin gap has been also observed in excitation spectra with the propagation vector parallel to the RuO 2 plane below 60 cm Ϫ1 at 7 K. These anisotropic properties have been obtained for a crystal with a high superconductivity transition temperature of 1.4 K. The sample quality is very important, since such an anisotropic property has not been observed in the Raman spectra for samples with T c ϭ0.97 K. The observed magnetic excitation suggests that the magnetic correlation is also important in understanding the mechanism of superconductivity of Sr 2 RuO 4 .

Physics Procedia, 2015

We have been developing Nb 3 Al wires processed by rapid heating and quenching for a number of ye... more We have been developing Nb 3 Al wires processed by rapid heating and quenching for a number of years as promising candidates for use in future high-field accelerator magnets. These wires have better strain and stress tolerances than Nb 3 Sn wires do, but to meet the demands of future accelerator magnet designs, it is necessary to further improve their performance. In particular, it is necessary to increase their non-copper critical current density in 12-20 T fields. To pursue this goal, we introduced double rapid heating and quenching (DRHQ) treatment into the fabrication process for Nb 3 Al wires, and studied the mechanical and superconducting properties of the resulting DRHQ-processed wires.

Journal of Alloys and Compounds, Feb 1, 2009

We have precisely investigated the antiferromagnetic transition in the ternary rare-earth metal s... more We have precisely investigated the antiferromagnetic transition in the ternary rare-earth metal silicide Er5Ir4Si10 single crystal by performing the high-resolution measurement of the low-temperature specific heat under zero-magnetic field and the AC nagnetization. In the temperature dependence of important physical quantities associated with the antiferromagnetic phase transition, we have observed anomalies associated with the antiferromagnetic long-range ordering at Neel temperature TN. We have confirmed that TN is 3.5 K. In addition, we have first observed two surprising results. Firstly, a shoulder was observed in the vicinity of 2K in addition to the sharp peak at TN corresponding to the antiferromagnetic long-range ordering in the high-resolution measurement of the low-temperature specific heat. Secondly, the anomaly of the AC magnetization at TN depends to the magnetic direction. Though we have clearly observed the anomaly of the AC magnetization assocated with the antiferromagnetic phase transition at TN when the AC magnetic field orientiation is parallel to the c-axis, we have observed no anomaly of the AC magnetization at TN when the AC magnetic field direction is perpendicular to the c-axis. These results clarify that our Er5Ir4Si10 single crystal is a quasi-two-dimensional antiferromagnet and then has no magnetic structure of the Er3+ local moments. However, we have observed a peak of AC magnetization around 2K when the AC magnetic field is perpendicular to the c-axis. This temperature corresponds to that at which a shoulder is observed in the high-resolusion measurement of the low-temperature specific heat. Furthermore, we have observed no frequency dependency of the AC magnetization which is ordinarily observed in the spin glass state. This result means that there is no disorder in our Er5Ir4Si10 single crystal because the crystal structure of Er5Ir4Si10 has the tetragonal crystal structure in which the octagons of Er3+ ions are stacked. In addition, both the tetragons and the octagons of Er3+ local moments have no magnetic frustration. At last we can conclude that both the shoulder of the low-temperature specific heat in the vicinity of 2K and the peak of the AC magnetization around 2K, which is only observed when the AC magnetic field direction is perpendicular to the c-axis, correspond to the crystallne electric field effet in the plane which is perpendicular to the c-axis of the tetragonal crystal structure.

IEEE Transactions on Applied Superconductivity, Jun 1, 2004

ABSTRACT

Synthetic Metals, 2014

An enantiomeric pair of chiral inducers with double chiral carbons was synthesized by a simple th... more An enantiomeric pair of chiral inducers with double chiral carbons was synthesized by a simple three-step reaction strategy. The process affords the chiral inducers with good yield, high enantiomeric excess, and good compatibility with nematic liquid crystal. Addition of a small amount of the chiral inducers thus synthesized in this study produced cholesteric architecture. Electrochemical polymerization in the asymmetric liquid crystal environment affords chiroptically active polymers as atropisomers. The electrochemical polymerization under magnetic field of 4 T affords polymer films with linear dichroism. The polymers exhibit a significant color change from dark-green in the oxidized state to light-green in the reduced state. The redox process of the polymer films in an electrolyte provides a reversible absorption, circular dichroism, and linear dichroism spectral changes.

Physical review, Aug 1, 2000

We have measured out-of-plane resistivity c for La 2Ϫx Sr x CuO 4 under anisotropic pressure. c-a... more We have measured out-of-plane resistivity c for La 2Ϫx Sr x CuO 4 under anisotropic pressure. c-axis compression, which decreases c , reduces T c drastically, whereas c-axis extension, which increases c , enhances T c from 38 K at ambient pressure to 51.6 K at 8 GPa. We find that the variation of T c scales as a function of c , and that the c-axis pressure coefficient is much stronger than the ab-axis one. These findings imply that T c depends primarily on the interlayer, rather than the in-plane, lattice parameter.

Polymer Journal, Apr 23, 2007

A facile method of simultaneous alignment and micropatterning of multi-wall carbon nanotubes (MWC... more A facile method of simultaneous alignment and micropatterning of multi-wall carbon nanotubes (MWCNTs) is presented. The method uses the combination of the magnetic alignment and patterning techniques. Due to their diamagnetic nature, MWCNTs suspended in a liquid medium are trapped at the minima of the magnetic field created by a field modulator and at the same time they align due to their magnetic anisotropy. The achieved patterning and alignment is fixed by solidification of the matrix. The alignments both parallel and perpendicular to the film surface have been achieved.

Materials advances, 2023

Oriented quasi-domain structure of helical spin polymers prepared by electrochemical polymerizati... more Oriented quasi-domain structure of helical spin polymers prepared by electrochemical polymerization in a cholesteric liquid crystal under a magnetic field, showing a helical stripe magnetic domain † Masashi Otaki, a Shigeki Nimori b and Hiromasa Goto * a We report the synthesis and alignment of organic radicals with helical structures. Helical spin p-conjugated polymers bearing organic radicals were synthesized by electrochemical polymerization in cholesteric liquid crystals under a magnetic field, using several types of oligothiophenes containing phenoxy radicals in the side chain as the monomers. Under the magnetic field, the polymerization proceeded in the helical liquid crystal matrix oriented in the direction of the magnetic field. These polymers were aligned with its helical axis perpendicular to a magnetic field of 6.0 T. In addition, electrochemical measurements showed that phenoxy radicals in the side chain and polarons as charge carriers in the main chain were respectively produced. The phenoxy radical with a g value of 2.00415 was confirmed from the electron spin resonance spectroscopy measurements. Superconducting quantum interference device magnetometry measurements revealed that these polymers thus obtained are paramagnetic materials. The optical texture and magnetic spectroscopy measurements indicate that the films thus prepared are helical spin polymers with an oriented quasi-domain structure, showing magneto-electro-optical activity. The optical texture corresponds to the helical stripe magnetic domain of the polymer. This method provides a novel approach for the fabrication of chiral magnets and molecular spin electronics.

IEEE Transactions on Applied Superconductivity, Jun 1, 2012

We have been developing rmNb3rmAl{\rm Nb}_{3}{\rm Al}rmNb3rmAl high-field accelerator magnets with the aim of upg... more We have been developing rmNb3rmAl{\rm Nb}_{3}{\rm Al}rmNb3rmAl high-field accelerator magnets with the aim of upgrading the luminosity of the Large Hadron Collider. In this program, four kinds of Ta-matrix rmNb3rmAl{\rm Nb}_{3}{\rm Al}rmNb3rmAl strands with slightly different cross-sectional structures (K1, K2, K3 and K4 strands) were designed and fabricated. The non-copper rmJrmc{\rm J}_{\rm c}rmJrmc values of these strands were 700–800 rmA/mm2{\rm A/mm}^{2}rmA/mm2 at 15 T and 4.2 K. The cabling work of these strands was performed at Fermilab, and the superconducting properties of the cables were studied using the extracted strands from the cables. In this paper, we report on the fabrication experience for the strands and cables. The results obtained from this study are also presented.

Polymers

A new method for fabricating conjugated polymer films was developed using electrochemical polymer... more A new method for fabricating conjugated polymer films was developed using electrochemical polymerization in liquid crystals and magnetic orientation. A uniaxial main chain orientation and a crosslinked network structure were achieved with this method. By employing eight types of monomers, the influence of the crosslinking for the film was investigated. The crosslinking was found to improve the solvent resistance of the conjugated polymer films. This new method is expected to be useful in various applications, such as high-powered organic electronic devices with durability.

Molecular Crystals and Liquid Crystals

IEEE Transactions on Applied Superconductivity, 2018

Refinement of Nb 3 Sn grain size by the generation of ZrO 2 precipitates in Nb 3 Sn wires," Appl.

Inorganic chemistry, Jan 20, 2016

We synthesize PbMn7O12 perovskite under high-pressure (6 GPa) and high-temperature (1373 K) condi... more We synthesize PbMn7O12 perovskite under high-pressure (6 GPa) and high-temperature (1373 K) conditions and investigate its structural, magnetic, dielectric, and ferroelectric properties. We find that PbMn7O12 exhibits rich physical properties from interplay among charge, orbital, and spin degrees of freedom and rich structural properties. PbMn7O12 crystallizes in space group R3̅ near room temperature and shows a structural phase transition at TCO = 397 K to a cubic structure in space group Im3̅; the Im3̅-to-R3̅ transition is associated with charge ordering. Below TOO = 294 K, a structural modulation transition associated with orbital ordering takes place. There are two magnetic transitions with Néel temperatures of TN1 = 83 K and TN2 = 77 K and probably a lock-in transition at TN3 = 43 K (on cooling). There is huge hysteresis on specific heat (between ∼37 and 65 K at 0 Oe), dielectric constant (between ∼20 and 70 K at 0 Oe), and dc and ac magnetic susceptibilities around the lock-in...

IEEE Transactions on Applied Superconductivity, 2015

The strengthening of Yoroi-coil (Y-based oxide superconductor and reinforcing outer integrated co... more The strengthening of Yoroi-coil (Y-based oxide superconductor and reinforcing outer integrated coil) structure at stronger electromagnetic force was investigated using the Yoroicoil structured double-pancake coil with higher strength outer plates of carbon-fiber reinforced plastic (C-FRP) than those of glass-FRP. The coil achieved 1.14 kA transporting at 4.2 K in 14-T backup magnetic field and the superconducting wire was burnt by thermal runaway after that. The calculated maximum hoop stress, based on the BJR (magnetic field × current density × coil radius) calculations, at the hoop stress test reached 2.0 GPa. This value was far exceeding the tensile strength of superconducting wire ranging from 1 to 1.3 GPa; however, the maximum strain of superconducting wire in the test coil was held about 0.5%. Yoroi-coil structure is useful for the applications, which need high magnetic field precision. The strengthening effect of C-FRP outer plates was observed at outer part of the coil, but it did not cover the whole coil body, so that arrangement of reinforcing outer plates could admit of some improvement.

Journal of the Physical Society of Japan, 1998

La (P1) and apical oxygen (P2) vibrations along the c-axis, which are A1g-symmetry in the tetrago... more La (P1) and apical oxygen (P2) vibrations along the c-axis, which are A1g-symmetry in the tetragonal phase (I4/mmm), have been systematically investigated for K2NiF4-type oxide superconductors; La2CuO4+delta (delta=0, 0.014, 0.063), La1.85Sr0.15CuO4, and Sr2RuO4. For La2CuO4+delta, with increasing of the excess oxygen concentration (delta), the intensity of P2 decreases exponentially as a function of delta at room temperature.This decrease can be

Solid State Communications, Sep 1, 2003

Using single crystals of Bi 2 Sr 2 CaCu 2 O 8 , a detailed study for the thermoremanent magnetiza... more Using single crystals of Bi 2 Sr 2 CaCu 2 O 8 , a detailed study for the thermoremanent magnetization (TRM) was performed at low AC applied field in the low temperature region ð5 # T # 20 KÞ: Below approximately 20 K, the AC susceptibility of TRM shows anomalous dispersion response with large amplitude. The origin of the unstable response has been discussed in relation with the pinning force.

Journal of the Physical Society of Japan, Jul 15, 1998

La (P1) and apical oxygen (P2) vibrations along the c-axis, which are A1g-symmetry in the tetrago... more La (P1) and apical oxygen (P2) vibrations along the c-axis, which are A1g-symmetry in the tetragonal phase (I4/mmm), have been systematically investigated for K2NiF4-type oxide superconductors; La2CuO4+delta (delta=0, 0.014, 0.063), La1.85Sr0.15CuO4, and Sr2RuO4. For La2CuO4+delta, with increasing of the excess oxygen concentration (delta), the intensity of P2 decreases exponentially as a function of delta at room temperature.This decrease can be

IEEE Transactions on Applied Superconductivity, Jun 1, 2006

ABSTRACT

Physical review, Mar 20, 2001

Physical review, Mar 15, 2001

We have systematically investigated the totally symmetric Raman-scattering spectra of Sr 2 RuO 4 ... more We have systematically investigated the totally symmetric Raman-scattering spectra of Sr 2 RuO 4 crystals in the temperature region between room temperature and 6 K. The electron-phonon interaction for the apical oxygen vibration has been experimentally investigated by a line-shape analysis based on the Fano interference model. It has been found that the electron-phonon interaction strongly depends on not only the polarization geometry but also the phonon-propagating direction. The phonon, which travels along the RuO 2 plane in the (a,a) geometry, shows the strongest electron-phonon interaction. The intensity of the broad background due to the magnetic excitation has been suppressed in the energy region less than 300 cm Ϫ1 at low temperature. Furthermore, the anisotropic formation of the spin gap has been also observed in excitation spectra with the propagation vector parallel to the RuO 2 plane below 60 cm Ϫ1 at 7 K. These anisotropic properties have been obtained for a crystal with a high superconductivity transition temperature of 1.4 K. The sample quality is very important, since such an anisotropic property has not been observed in the Raman spectra for samples with T c ϭ0.97 K. The observed magnetic excitation suggests that the magnetic correlation is also important in understanding the mechanism of superconductivity of Sr 2 RuO 4 .

Physics Procedia, 2015

We have been developing Nb 3 Al wires processed by rapid heating and quenching for a number of ye... more We have been developing Nb 3 Al wires processed by rapid heating and quenching for a number of years as promising candidates for use in future high-field accelerator magnets. These wires have better strain and stress tolerances than Nb 3 Sn wires do, but to meet the demands of future accelerator magnet designs, it is necessary to further improve their performance. In particular, it is necessary to increase their non-copper critical current density in 12-20 T fields. To pursue this goal, we introduced double rapid heating and quenching (DRHQ) treatment into the fabrication process for Nb 3 Al wires, and studied the mechanical and superconducting properties of the resulting DRHQ-processed wires.

Journal of Alloys and Compounds, Feb 1, 2009

We have precisely investigated the antiferromagnetic transition in the ternary rare-earth metal s... more We have precisely investigated the antiferromagnetic transition in the ternary rare-earth metal silicide Er5Ir4Si10 single crystal by performing the high-resolution measurement of the low-temperature specific heat under zero-magnetic field and the AC nagnetization. In the temperature dependence of important physical quantities associated with the antiferromagnetic phase transition, we have observed anomalies associated with the antiferromagnetic long-range ordering at Neel temperature TN. We have confirmed that TN is 3.5 K. In addition, we have first observed two surprising results. Firstly, a shoulder was observed in the vicinity of 2K in addition to the sharp peak at TN corresponding to the antiferromagnetic long-range ordering in the high-resolution measurement of the low-temperature specific heat. Secondly, the anomaly of the AC magnetization at TN depends to the magnetic direction. Though we have clearly observed the anomaly of the AC magnetization assocated with the antiferromagnetic phase transition at TN when the AC magnetic field orientiation is parallel to the c-axis, we have observed no anomaly of the AC magnetization at TN when the AC magnetic field direction is perpendicular to the c-axis. These results clarify that our Er5Ir4Si10 single crystal is a quasi-two-dimensional antiferromagnet and then has no magnetic structure of the Er3+ local moments. However, we have observed a peak of AC magnetization around 2K when the AC magnetic field is perpendicular to the c-axis. This temperature corresponds to that at which a shoulder is observed in the high-resolusion measurement of the low-temperature specific heat. Furthermore, we have observed no frequency dependency of the AC magnetization which is ordinarily observed in the spin glass state. This result means that there is no disorder in our Er5Ir4Si10 single crystal because the crystal structure of Er5Ir4Si10 has the tetragonal crystal structure in which the octagons of Er3+ ions are stacked. In addition, both the tetragons and the octagons of Er3+ local moments have no magnetic frustration. At last we can conclude that both the shoulder of the low-temperature specific heat in the vicinity of 2K and the peak of the AC magnetization around 2K, which is only observed when the AC magnetic field direction is perpendicular to the c-axis, correspond to the crystallne electric field effet in the plane which is perpendicular to the c-axis of the tetragonal crystal structure.

IEEE Transactions on Applied Superconductivity, Jun 1, 2004

ABSTRACT

Synthetic Metals, 2014

An enantiomeric pair of chiral inducers with double chiral carbons was synthesized by a simple th... more An enantiomeric pair of chiral inducers with double chiral carbons was synthesized by a simple three-step reaction strategy. The process affords the chiral inducers with good yield, high enantiomeric excess, and good compatibility with nematic liquid crystal. Addition of a small amount of the chiral inducers thus synthesized in this study produced cholesteric architecture. Electrochemical polymerization in the asymmetric liquid crystal environment affords chiroptically active polymers as atropisomers. The electrochemical polymerization under magnetic field of 4 T affords polymer films with linear dichroism. The polymers exhibit a significant color change from dark-green in the oxidized state to light-green in the reduced state. The redox process of the polymer films in an electrolyte provides a reversible absorption, circular dichroism, and linear dichroism spectral changes.

Physical review, Aug 1, 2000

We have measured out-of-plane resistivity c for La 2Ϫx Sr x CuO 4 under anisotropic pressure. c-a... more We have measured out-of-plane resistivity c for La 2Ϫx Sr x CuO 4 under anisotropic pressure. c-axis compression, which decreases c , reduces T c drastically, whereas c-axis extension, which increases c , enhances T c from 38 K at ambient pressure to 51.6 K at 8 GPa. We find that the variation of T c scales as a function of c , and that the c-axis pressure coefficient is much stronger than the ab-axis one. These findings imply that T c depends primarily on the interlayer, rather than the in-plane, lattice parameter.

Polymer Journal, Apr 23, 2007

A facile method of simultaneous alignment and micropatterning of multi-wall carbon nanotubes (MWC... more A facile method of simultaneous alignment and micropatterning of multi-wall carbon nanotubes (MWCNTs) is presented. The method uses the combination of the magnetic alignment and patterning techniques. Due to their diamagnetic nature, MWCNTs suspended in a liquid medium are trapped at the minima of the magnetic field created by a field modulator and at the same time they align due to their magnetic anisotropy. The achieved patterning and alignment is fixed by solidification of the matrix. The alignments both parallel and perpendicular to the film surface have been achieved.

Materials advances, 2023

Oriented quasi-domain structure of helical spin polymers prepared by electrochemical polymerizati... more Oriented quasi-domain structure of helical spin polymers prepared by electrochemical polymerization in a cholesteric liquid crystal under a magnetic field, showing a helical stripe magnetic domain † Masashi Otaki, a Shigeki Nimori b and Hiromasa Goto * a We report the synthesis and alignment of organic radicals with helical structures. Helical spin p-conjugated polymers bearing organic radicals were synthesized by electrochemical polymerization in cholesteric liquid crystals under a magnetic field, using several types of oligothiophenes containing phenoxy radicals in the side chain as the monomers. Under the magnetic field, the polymerization proceeded in the helical liquid crystal matrix oriented in the direction of the magnetic field. These polymers were aligned with its helical axis perpendicular to a magnetic field of 6.0 T. In addition, electrochemical measurements showed that phenoxy radicals in the side chain and polarons as charge carriers in the main chain were respectively produced. The phenoxy radical with a g value of 2.00415 was confirmed from the electron spin resonance spectroscopy measurements. Superconducting quantum interference device magnetometry measurements revealed that these polymers thus obtained are paramagnetic materials. The optical texture and magnetic spectroscopy measurements indicate that the films thus prepared are helical spin polymers with an oriented quasi-domain structure, showing magneto-electro-optical activity. The optical texture corresponds to the helical stripe magnetic domain of the polymer. This method provides a novel approach for the fabrication of chiral magnets and molecular spin electronics.

IEEE Transactions on Applied Superconductivity, Jun 1, 2012

We have been developing rmNb3rmAl{\rm Nb}_{3}{\rm Al}rmNb3rmAl high-field accelerator magnets with the aim of upg... more We have been developing rmNb3rmAl{\rm Nb}_{3}{\rm Al}rmNb3rmAl high-field accelerator magnets with the aim of upgrading the luminosity of the Large Hadron Collider. In this program, four kinds of Ta-matrix rmNb3rmAl{\rm Nb}_{3}{\rm Al}rmNb3rmAl strands with slightly different cross-sectional structures (K1, K2, K3 and K4 strands) were designed and fabricated. The non-copper rmJrmc{\rm J}_{\rm c}rmJrmc values of these strands were 700–800 rmA/mm2{\rm A/mm}^{2}rmA/mm2 at 15 T and 4.2 K. The cabling work of these strands was performed at Fermilab, and the superconducting properties of the cables were studied using the extracted strands from the cables. In this paper, we report on the fabrication experience for the strands and cables. The results obtained from this study are also presented.

Polymers

A new method for fabricating conjugated polymer films was developed using electrochemical polymer... more A new method for fabricating conjugated polymer films was developed using electrochemical polymerization in liquid crystals and magnetic orientation. A uniaxial main chain orientation and a crosslinked network structure were achieved with this method. By employing eight types of monomers, the influence of the crosslinking for the film was investigated. The crosslinking was found to improve the solvent resistance of the conjugated polymer films. This new method is expected to be useful in various applications, such as high-powered organic electronic devices with durability.

Molecular Crystals and Liquid Crystals

IEEE Transactions on Applied Superconductivity, 2018

Refinement of Nb 3 Sn grain size by the generation of ZrO 2 precipitates in Nb 3 Sn wires," Appl.

Inorganic chemistry, Jan 20, 2016

We synthesize PbMn7O12 perovskite under high-pressure (6 GPa) and high-temperature (1373 K) condi... more We synthesize PbMn7O12 perovskite under high-pressure (6 GPa) and high-temperature (1373 K) conditions and investigate its structural, magnetic, dielectric, and ferroelectric properties. We find that PbMn7O12 exhibits rich physical properties from interplay among charge, orbital, and spin degrees of freedom and rich structural properties. PbMn7O12 crystallizes in space group R3̅ near room temperature and shows a structural phase transition at TCO = 397 K to a cubic structure in space group Im3̅; the Im3̅-to-R3̅ transition is associated with charge ordering. Below TOO = 294 K, a structural modulation transition associated with orbital ordering takes place. There are two magnetic transitions with Néel temperatures of TN1 = 83 K and TN2 = 77 K and probably a lock-in transition at TN3 = 43 K (on cooling). There is huge hysteresis on specific heat (between ∼37 and 65 K at 0 Oe), dielectric constant (between ∼20 and 70 K at 0 Oe), and dc and ac magnetic susceptibilities around the lock-in...

IEEE Transactions on Applied Superconductivity, 2015

The strengthening of Yoroi-coil (Y-based oxide superconductor and reinforcing outer integrated co... more The strengthening of Yoroi-coil (Y-based oxide superconductor and reinforcing outer integrated coil) structure at stronger electromagnetic force was investigated using the Yoroicoil structured double-pancake coil with higher strength outer plates of carbon-fiber reinforced plastic (C-FRP) than those of glass-FRP. The coil achieved 1.14 kA transporting at 4.2 K in 14-T backup magnetic field and the superconducting wire was burnt by thermal runaway after that. The calculated maximum hoop stress, based on the BJR (magnetic field × current density × coil radius) calculations, at the hoop stress test reached 2.0 GPa. This value was far exceeding the tensile strength of superconducting wire ranging from 1 to 1.3 GPa; however, the maximum strain of superconducting wire in the test coil was held about 0.5%. Yoroi-coil structure is useful for the applications, which need high magnetic field precision. The strengthening effect of C-FRP outer plates was observed at outer part of the coil, but it did not cover the whole coil body, so that arrangement of reinforcing outer plates could admit of some improvement.

Journal of the Physical Society of Japan, 1998

La (P1) and apical oxygen (P2) vibrations along the c-axis, which are A1g-symmetry in the tetrago... more La (P1) and apical oxygen (P2) vibrations along the c-axis, which are A1g-symmetry in the tetragonal phase (I4/mmm), have been systematically investigated for K2NiF4-type oxide superconductors; La2CuO4+delta (delta=0, 0.014, 0.063), La1.85Sr0.15CuO4, and Sr2RuO4. For La2CuO4+delta, with increasing of the excess oxygen concentration (delta), the intensity of P2 decreases exponentially as a function of delta at room temperature.This decrease can be