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The 5d pyrochlore oxide Cd2Re2O7 exhibits successive phase transitions from a cubic pyrochlore structure (phase I) to a tetragonal structure without inversion symmetry below Ts1 of ~200 K (phase II) and further to another noncentrosymmetric tetragonal structure below Ts2 of ~120 K (phase III). The two low-temperature phases may be characterized by odd-parity multipolar orders induced by the Fermi liquid instability of the spin-orbit-coupled metal. To control the tetragonal domains generated by the transitions and to obtain a single-domain crystal for the measurements of anisotropic properties, we prepared single crystals with the (0 0 1) surface and applied biaxial and uniaxial stresses along the plane. Polarizing optical microscopy observations revealed that inducing a small strain of approximately 0.05% could flip the twin domains ferroelastically in a reversible fashion at low temperatures, which evidences that the tetragonal deformation switches at Ts2 between c > a for phase II and c < a for phase III. Resistivity measurements using single-domain crystals under uniaxial stress showed that the anisotropy was maximum at around Ts2 and turned over across Ts2: resistivity along the c axis is larger (smaller) than that along the a axis by ~25% for phase II (III) at around Ts2. These large anisotropies probably originate from spin-dependent scattering in the spin-split Fermi surfaces of the cluster electric toroidal quadrupolar phases of Cd2Re2O7., 16 pages, 13 figures, J. Phys. Soc. Jpn in press

This study investigates the transport properties of a chiral elemental semiconductor tellurium (Te) under magnetic fields and pressure. Application of hydrostatic pressure reduces the resistivity of Te, while its temperature dependence remains semiconducting up to 4 GPa, contrary to recent theoretical and experimental studies. Application of higher pressure causes structural as well as semiconductor--metal transitions. The resulting metallic phase above 4 GPa exhibits superconductivity at 2 K along with a noticeable linear magnetoresistance effect. On the other hand, at ambient pressure, we identified metallic surface states on the as-cleaved (10$\bar{1}$0) surfaces of Te. The nature of these metallic surface states has been systematically studied by analyzing quantum oscillations observed in high magnetic fields. We clarify that a well-defined metallic surface state exists not only on chemically etched samples that were previously reported, but also on as-cleaved ones., 6 pages, 5 figures

Optical absorption spectra of solid oxygen α phase and liquid oxygen were measured in high magnetic fields over 100 T using a single turn coil method. The absorption originates from the bimolecular transition was observed. The spectra strongly reflect the local magnetic interaction between two oxygen molecules. The shape of the absorption spectrum of the α oxygen changed dramatically with increasing magnetic fields, even though the absorption intensity of liquid oxygen simply declined. This difference cannot be explained by only the local magnetic interaction, and we speculate that the field induced lattice distortion plays an important role in the solid oxygen α phase.

An overview of the crystal structures and physical properties of the recently discovered iron-platinum-arsenide superconductors, Ca10(PtnAs8)(Fe2-xPtxAs2)5 (n = 3 and 4), which have a superconducting transition temperature up to 38 K, is provided. The crystal structure consists of superconducting Fe2As2 layers alternating with platinum-arsenic layers, PtnAs8. The upper critical field Hc2, hydrostatic pressure dependence of superconducting transition temperature Tc, and normal-state magnetic susceptibility are reported., 7 pages, 6 figures

Adsorption isotherms of N 2 , O 2 , CO 2 , and Xe on a flexible microporous coordination polymer, CPL-2 [Cu 2 (pzdc) 2 (bpy)]·(pzdc = pyrazine-2,3-dicarboxylate; bpy = 4,4'-bipyridine), possessing bellows-shaped one-dimensional channels were measured. A nonintegral number of each of the N 2 , O 2 , CO 2 , and Xe molecules can be accommodated in each unit pore, which indicates that all guest molecules are accommodated in the so-called "incommensurate fashion". In situ synchrotron X-ray powder diffraction patterns of CPL-2 with guest molecules were recorded. The unit cells were determined from each pattern. It was found that the host CPL-2 exhibits different crystal transformation with the accommodation of each guest molecule. This indicates that, even in the case of incommensurate adsorption, the flexible framework of a microporous coordination polymer can transform each pore to suit different guest molecules.

Molecules and atoms confined in a nanospace may have properties distinctly different from those of the bulk fluid, owing to the formation of a specific molecular array characteristic of nanospace. In situ synchrotron powder X-ray diffraction measurements have been used to observe confined guest molecules such as N2, O2, Ar, and CH4 in the well-regulated ultramicropore of a copper coordination polymer, 1 ([Cu2(pzdc)2pyz]: pzdc = 2,3-pyrazinedicarboxylate and pyz = pyrazine). The obtained crystal structures indicate that guest molecules are confined in a linear fashion to form crystalline-like regular ordered arrays, in contrast to the situation in the gas and liquid state, even at temperatures above the boiling point, and the ordered arrays are characteristic of the kind of gas molecule and the geometrical and potential properties of the ultramicropore of 1.

We have measured the electrical resistivity of an antiferromagnetic Kondo compound CeNiGe3 under pressure. The Neel temperature initially increases with pressure P up to 3 GPa, then decreases rather steeply with further increasing pressure, and becomes zero at a critical pressure GPa. The A and ρ0 values of the resistivity ρ = ρ0+AT2 in the Fermi liquid relation become maximum around Pc, the A value attaining an extremely large value which is comparable with that in a heavy fermion superconductor CeCu2Si2. Superconductivity is found below 0.48 K in a wide pressure region from 4 to 10 GPa. The upper critical field Hc 2(0) is about 2 T, indicating heavy fermion superconductivity.

The Knight shift K and the nuclear spin–lattice relaxation time T1 of 7Li have been measured under high pressure up to 4.74 GPa. 1/T1T becomes larger on applying higher pressure below 10 K and does not obey the T1T = constant relation down to 1 K. Meanwhile, K is independent of pressure above 2 GPa, indicating that the uniform component of the susceptibility does not change under high pressure. These results indicate that some antiferromagnetic fluctuations with wavevector dominate the relaxation rate in LiV2O4 near the boundary of the pressure induced insulating phase. It is noted that the pressure dependence of T1 for LiV2O4 is opposite to that of typical Ce HF compounds, such as CeCu5.9Au0.1 and CeCu2Si2. At the highest pressure of 4.74 GPa, we found that 1/T1 obeys a power law dependence of T2/3 over the wide T range between 60 mK and 10 K. The spin dynamics under high pressure will be discussed.

We report the discovery of pressure-induced superconductivity in ferromagnetic UIr, which lacks inversion symmetry in the crystal structure. The Curie temperature TC1 = 46 K at ambient pressure decreases with increasing pressure, reaching a value of 11 K at 1.5 GPa. It presumably decreases further up to about Pc1 = 1.7 GPa. The ferromagnetic region named 'F1' exists up to Pc1. A second magnetic phase named 'F2' with a low ferromagnetic moment appears in the pressure range from 1.9 to 2.4 GPa. In the 'F2' phase, the magnetic transition temperature TC2 decreases with pressure, from 18 K at 1.9 GPa to approximately zero at PC2 = 2.6–2.7 GPa. In this critical pressure region, superconductivity appears below Tsc = 0.14 K.

We have measured the electrical resistivity under pressure up to 2 GPa for an antiferromagnet, CeRhGe. The resistivity at ambient pressure decreases monotonically below a Neel temperature TN = 10 K. With increasing pressure P, the resistivity has a peak around 10 K, which is anomalously enhanced up to 1.2 GPa. With further increasing pressure, the resistivity peak is diminished; the Neel temperature becomes zero at a critical pressure Pc = 1.9 GPa. The A-value of the resistivity ρ in the Fermi liquid relation ρ = ρ0 + AT2 is also found to increase with increasing pressure and has a maximum at Pc which corresponds to the value for the heavy-fermion superconductor CeCu2Si2.

When pressure is applied to cerium and uranium compounds, the magnetic ordering temperature is suppressed and becomes zero at a critical pressure P c . Around P c , non-Fermi liquid and/or superconductivity are observed. We clarified a change of the electronic state via a de Haas–van Alphen (dHvA) experiment when pressure crosses P c . The dHvA experiment under pressure was done for the antiferromagnets CeRh 2 Si 2 and CeRhIn 5 , and for a ferromagnet UGe 2 . We found an abrupt change of the Fermi surface for CeRh 2 Si 2 and UGe2 when crossing P c , indicating a first-order like phase transition. For CeRhIn 5 , the topology of the Fermi surface was unchanged, but the cyclotron mass increased steeply above 1.6 Gpa, where superconductivity sets in.

We have studied the effect of pressure on the electrical resistivity of a high-quality single crystal CeAgSb2 which has a small net ferromagnetic moment of 0.4μB/Ce. The magnetic ordering temperature Tord = 9.7 K decreases with increasing pressure p and disappears at a critical pressure pc 3.3 GPa. The residual resistivity, which is close to zero up to 3 GPa, increases steeply above 3 GPa, reaching 55μΩ cm at pc. A huge residual resistivity is found to appear when the magnetic order disappears.

We have developed high-pressure NMR technique with an Indenter Cell using NiCrAl alloy. It was designed to set easily into a conventional dilution fridge and/or high field magnet. We have succeeded in 7Li-NMR measurement of a heavy fermion spinel LiV2O4 in T-range between 60 mK and 30 K under pressure up to 4.7 GPa. At ambient pressure, 1/T1 shows a broad maximum around 50 K and is proportional to the temperature below 6 K. This is quite similar to the relaxation behavior in f-electron HF systems. However, 1/T1T becomes larger with applying higher pressure below 10 K and does not obey T1T = constant relation down to 1 K. Knight shift K, meanwhile, is independent of pressure above 2 GPa, indicating that the uniform component of susceptibility χ(0) does not change under high pressure. Some antiferromagnetic fluctuations with wave vector q ≠ 0 dominate relaxation rate in LiV2O4 near the boundary of the pressure induced insulating phase.

We carried out the de Haas–van Alphen (dHvA) experiment under pressure to clarify the nature of f-electron compounds of CeRh2Si2, UGe2 and CeCoIn5. With increasing pressure, the Neel temperature T N =36 K in CeRh2Si2 and the Curie temperature T C =52 K in UGe2 decrease, and a quantum critical point corresponding to the extrapolation TN or TC→0 is reached at the critical pressure pc≃1.06 and 1.52 GPa, respectively. Experimental results indicate a discontinuous change of the Fermi surface in CeRh2Si2 and UGe2 when the pressure crosses pc. A heavy fermion superconductor CeCoIn5 with a quasi-two dimensional Fermi surface was found to be located in the vicinity of the quantum critical point.

We have studied the effect of pressure on the electrical resistivity of the antiferromagnet CeMg2Cu9 which crystallizes in the hexagonal structure. The structure is built up of alternating MgCu2 Laves-type and CeCu5-type layers along the [0001] direction. The N?el temperature TN = 2.7?K at ambient pressure decreases with increasing pressure p and disappears at a critical pressure pc2.5?GPa. Correspondingly, the residual resistivity ?0 and the coefficient A in a Fermi-liquid relation ? = ?0 + AT2 are found to have maximum values around pc.

The superconducting pyrochlore oxide Cd2Re2O7 is revisited with a particular emphasis on the sample-quality issue. The compound has drawn attention as the only superconductor (Tc = 1.0 K) that has been found in the family of {\alpha}-pyrochlore oxides since its discovery in 2001. Moreover, it exhibits two characteristic structural transitions from the cubic pyrochlore structure, with the inversion symmetry broken at the first one at 200 K. Recently, it has attracted increasing attention as a candidate spin-orbit coupled metal (SOCM), in which specific Fermi liquid instability is expected to lead to an odd-parity order with spontaneous inversion-symmetry breaking [L. Fu, Phys. Rev. Lett. 115, 026401 (2015)] and parity-mixing superconductivity [V. Kozii and L. Fu: Phys. Rev. Lett. 115 (2015) 207002; Y. Wang et al., Phys. Rev. B 93 (2016) 134512]. We review our previous experimental results in comparison with those of other groups in the light of the theoretical prediction of the SOCM, which we consider meaningful and helpful for future progress in understanding this unique compound., Comment: 15 pages, 11 figures, J. Phys. Soc. Jpn, in press

The effects of pressure on antiferromagnetic (AFM) and superconducting phase transitions of 112-type Ca$_{1-x}$La$_{x}$FeAs$_{2}$ were studied, and the in-plane electrical resistivity $\rho_{ab}$ was measured with an indenter-type pressure cell. The AFM phase transition temperatures of $T_{\rm N}$ = 47, 63, and 63 K at ambient pressure for $x$ = 0.18, 0.21, and 0.26 was suppressed by applying pressure $P$, with superconductivity emerging at critical pressures of $P_{\rm c}$ $\simeq$ 0, 1.5, and 3.4 GPa, respectively. Correspondingly, the slope of $T_{\rm N}$ against $P$ decreased as $dT_{\rm N}/P$ $\simeq$ $-$15 and $-$2 K/GPa for $x$ = 0.21 and 0.26, respectively. Thus, although the AFM phase was stabilized with La doping $x$, the AFM phase was suppressed by pressure, and superconductivity eventually emerged., Comment: 4 pages, 2 figures, Note added after publication: We noticed a paper by Yazhou Zhou et al. [Science Bulletin, 62, 857(2017)] reporting the pressure-induced superconductivity in the 112 system

We have performed the de Haas-van Alphen (dHvA) and ac-susceptibility experiments on a ferromagnet UGe2 under pressure for the field along the easy a-axis. The p-H phase diagram was determined, indicating three kinds of phase: paramagnetic and weakly and strongly polarized phases. The detected dHvA frequencies as well as the cyclotron masses are found to be very different between the weakly and strongly polarized states. A change of the Fermi surface occurs when the weakly polarized phase is changed into the strongly polarized phase with increasing magnetic field.

We carried out the de Haas-van Alphen (dHvA) experiment under pressure for a ferromagnet UGe2. The dHvA frequency of a main dHvA branch named α, that corresponds to a majority up-spin band 40-hole Fermi surface, decreases monotonously with increasing pressure, but in the pressure range from pc* (1.2 GPa) to pc (1.5 GPa) the dHvA signal disappears completely, where pc and pc* correspond to critical pressures for a Curie temperature TC and the second phase transition temperature T* ( pc we observed new dHvA branches with large cyclotron masses of 19-64m0, which correspond to main Fermi surfaces in the paramagnetic state.

We have measured nuclear quadrupole resonance (NQR) for 63 Cu nuclei under high pressure up to 4.8 GPa. A linear increase in NQR frequency 63 v Q of 63 Cu nuclei was observed below 3 GPa. However, 63 v Q deviates gradually from the linear relation above 3.5 GPa. The downward deviation is associated with a change of valence and consistent with the results of band calculations with the structural parameters under pressure. Antiferromagnetic (AFM) spin fluctuations are drastically suppressed with increasing pressure, whereas T c increases from 0.7 K at ambient pressure to 1.64 K at 4.2 GPa. We have found that bulk superconductivity suddenly disappears at 4.8 GPa accompanied with a rapid decrease in the density of states at the Fermi level.

We confirmed bulk-superconductivity of a ferromagnet UGe2 by the specific heat measurement, together with the measurements of the electrical resistivity and ac susceptibility, in a pressure range from p = 1.0 to 1.5 GPa, where the Curie temperature TC( = 22-36 K) is still high, but another characteristic temperature T* is close to zero. In this pressure range, the heavy fermion state is found to be formed at low temperatures.

A review of recent developments in high-pressure techniques and their application in the search for superconductivity at low temperature is presented. We have focused the discussion mainly on the experimental results obtained by our group for simple molecular systems.

The pressure range for electrical transport measurements has been dramatically increased up to 220 GPa in the 0.05-300 K temperature region and at magnetic fields of up to 10 T. Metallization of caesium iodide was found at a pressure of 115 GPa. A superconducting transition with was observed above 180 GPa. decreases with increasing pressure. The superconducting transition shifts to lower temperatures and disappears under magnetic field above 0.3 Tesla.

Magnetic susceptibilities of 5 kinds of 3-(4-R-phenyl)-1,5-dimethyl-6-oxoverdazyl radicals (PDOV (R=H), p-MDOV (R=CH3O), p-MeDOV (R=CH3), p-CyDOV (R=CN), and p-NDOV (R=NO2)) have been measured in the temperature range of 4.2–300 K. The susceptibilities of PDOV, p-MDOV, and p-MeDOV can be explained by an antiferromagnetic Heisenberg alternating chain model. The susceptibility of p-CyDOV shows a broad maximum at 54 K, and decreases abruptly at 15 K, suggesting a spin-Peierls transition. High-field magnetization data (H = 0 to 35 T) which provide a clear evidence for a spin-Peierls transition were reported. The magnetic susceptibilities of diluted crystal, (p-CyDOV)1-x(p-CyDOV- H)x (x = 0 ∼ 0.10), were measured to study the effects of nonmagnetic impurities, p-CyDOV-H (amine precursor of p-CyDOV), on the spin-Peierls transition. The transition temperature reduced rapidly upon p-CyDOV-H substitution and the spin-Peierls state disappeared around x = 0.07.

Magnetic properties of oxygen physisorbed in Cu-trans-1,4-cyclohexanedicarboxylic acid having one-dimensional micropores are studied. O2 is well known as a magnetic molecule with S=1. In the case of the low adsorption, temperature dependence of the susceptibility shows the Schottky-type broad peak and the high-field magnetization process has a step at around 34T with saturation moment of 2 μ B/O2. These results are interpreted by the dimer model of S=½ with an antiferromagnetic exchange interaction. Broadening of the step of magnetization with increasing the adsorption may be due to the inter-dimer interaction or the distribution of the intra-dimer exchange interaction. Linear magnetization process which is characteristic of one-dimensional Heisenberg antiferromagnet has not been observed even in the full pore region.

The magnetic properties of N-[(dichlorophenyl)thio]-2,4,6-tris(chlorophenyl)phenylaminyl radical crystals are reported. The stable radical crystals of N-[(2,4-dichlorophenyl)thio]-2,4,6-tris(4-chlorophenyl)phenylaminyl (1) and N-[(2,4-dichlorophenyl)thio]-2,4,6-tris(3-chlorophenyl)phenylaminyl (2) have shown one-dimensional ferromagnetic behavior which have described using the Bonner-Fisher model with the large ferromagnetic exchange interaction of J/kB = 14.0 K and J/kB = 5.7 K, respectively. In addition to these ferromagnetic compounds, N-[(3,5-dichlorophenyl)thio]-2,4,6-tris(4-chlorophenyl)phenylaminyl (3) has also shown the ferromagnetic intermolecular exchange interaction of J/kB = 1.8 K. For these crystals, we have carried out low-temperature susceptibility and heat capacity measurements below 2 K. Radical 1 has shown a magnetic phase transition at 0.4 K. The susceptibility in the ordered state, however, shows spinflip transition, indicating antiferromagnetic long range ordering. For the or...

Magnetic property of 3-(4-cyanophenyl)-1,5-diphenyl-6-thioxoverdazyl (p-CyDpTV) radical crystal has been studied in the temperature range of 0.05–300 K in external magnetic fields 3, 11, 30, and 100 Oe by using SQUID magnetometer. Weak ferromagnetic behavior was observed at TN = 0.41 K. Below TN, the spontaneous magnetization Ms(T) increased rapidly, reaching a maximum of 31.1 emu/mol at 0.05 K. Spin-canting angle was estimated to be 0.32° at 0.05 K. Near TN, M s (T) ∝ [1 − ( T T N )] β with the critical exponent of β = 0.36, in agreement with that expected for an isotropic three-dimensional (3D) Heisenberg spin system.

The magnetic properties of N-[(dichlorophenyl)thio]-2,4,6-triarylphenylaminyl radical crystals are reported. The three stable thioaminyls show ferromagnetic behaviors described using the one-dimensional Heisenberg model with the large ferromagnetic interaction of 2 J / k B = 28.0, 11.4, and 3.6 K. The other two radicals show the antiferromagnetic alternating chain behaviors with 2 J / k B = −16.8 K, α = 0.55 and 2 J / k B = −128.8 K, α = 0.90. The low-temperature susceptibility and heat capacity measurements of the crystal showing 2 J / k B = 28.0 K reveal a magnetic phase transition at 0.4 K. The ordered phase shows spin-flop transition which reveals an antiferromagnetic long range order.

A new three-dimensional (3-D) jungle-gym-like open metal-organic framework has been synthesized from a two-dimensional (2-D) layer compound using a heterogeneous pillar insertion reaction. Both the starting 2-D layer and the resulting 3-D open compounds have been characterized using X-ray crystallography.

The magnetic properties of molecular oxygen adsorbed in the micro-porous metal-organic solids have been investigated. Adsorbed O 2 molecules form a ladder structure in the nanochannels of CPL-1. The temperature dependence of susceptibility and the high-field magnetization process indicate the nonmagnetic ground state of the adsorbed O 2 at low temperatures.

Potassium-doped picene (K3.0picene) with a superconducting transition temperature (T C) as high as 14 K at ambient pressure has been prepared using an annealing technique. The shielding fraction of this sample was 5.4% at 0 GPa. The T C showed a positive pressure-dependence and reached 19 K at 1.13 GPa. The shielding fraction also reached 18.5%. To investigate the chemical composition and the state of the picene skeleton in the superconducting sample, we used energy-dispersive x-ray (EDX) spectroscopy, MALDI-time-of-flight (MALDI-TOF) mass spectroscopy and x-ray diffraction (XRD). Both EDX and MALDI-TOF indicated no contamination with materials other than K-doped picene or K-doped picene fragments, and supported the preservation of the picene skeleton. However, it was also found that a magnetic K-doped picene sample consisted mainly of picene fragments or K-doped picene fragments. Thus, removal of the component contributing the magnetic quality to a superconducting sample should enhance the volume fraction.

Effects of Cu-impurity are studied by heat capacity and susceptibility measurements down to 30 mK on the Haldane-gap antiferromagnet Ni(C 2 H 8 N 2 ) 2 NO 2 (ClO 4 ) (NENP). We have observed the characteristic heat capacity and susceptibility which show contributions from free spins of the Cu 2+ -impurities with S =1/2 and the fractional spin S =1/2 states at the ends of the Ni 2+ ( S =1)-chain adjacent to the Cu 2+ -impurities. The present results are explained completely by the phenomenological Hamiltonian for a trimmer of S =1/2 proposed by the ESR study on this system.

The dc magnetization of insulating UO2 under high pressure up to ~1 GPa has been measured using a piston–cylinder cell. Pressure-induced weak ferromagnetism appeared at low pressure (~0.2 GPa). Both the remanent magnetization and the coercive force increase as pressure increases. This weak ferromagnetism may come from spin canting or from uncompensated moments around grain boundaries.

The magnetic properties of 4-methacryloyloxy- and 4-acryloyloxy-2,2,6,6-tetramethylpiperidine-l-oxyl (MOTMP and AOTMP, respectively) were studied. The magnetic susceptibility, magnetization, and molar heat capacity of MOTMP show that the crystal has one-dimensional ferromagnetic coupling, and that the coupling between the one-dimensional coupling chains was antiferromagnetic, resulting in a metamagnet below 0.16 K. On the other hand, AOTMP, where hydrogen atom is substituted for a methyl group at α-position, shows an antiferromagnetic coupling between the nitroxyl radicals.

Metal-organic microporous materials (MOMs) have attracted wide scientific attention owing to their unusual structure and properties, as well as commercial interest due to their potential applications in storage, separation and heterogeneous catalysis. One of the advantages of MOMs compared to other microporous materials, such as activated carbons, is their ability to exhibit a variety of pore surface properties such as hydrophilicity and chirality, as a result of the controlled incorporation of organic functional groups into the pore walls. This capability means that the pore surfaces of MOMs could be designed to adsorb specific molecules; but few design strategies for the adsorption of small molecules have been established so far. Here we report high levels of selective sorption of acetylene molecules as compared to a very similar molecule, carbon dioxide, onto the functionalized surface of a MOM. The acetylene molecules are held at a periodic distance from one another by hydrogen bonding between two non-coordinated oxygen atoms in the nanoscale pore wall of the MOM and the two hydrogen atoms of the acetylene molecule. This permits the stable storage of acetylene at a density 200 times the safe compression limit of free acetylene at room temperature.

Electrical resistance of Ca is measured under pressures up to 150 GPa and at temperatures down to 0.05 K. Superconductivity is observed at temperatures below 3 K under pressures above 85 GPa. The superconducting transition temperature increases linearly with increasing pressure and reaches about 15 K at 150 GPa.

In situ synchrotron X-ray powder diffraction patterns of porous coordination polymers [[Cu(2)(pzdc)(2)(bpy)].G] have been measured (pzdc = pyrazine-2,3-dicarboxylate, bpy = 4,4'-bipyridine) (where G = H(2)O for CPL-2 superset H(2)()O, G = benzene for CPL-2 superset benzene, and G = void for the apohost). The structures of apohost and CPL-2 superset benzene were determined from Rietveld analysis. Adsorption of benzene in the channels induced a remarkable contraction in the crystal (b axis; 6.8%, volume; 4.9%), although the channels were occupied by the benzene molecules. This crystal transformation provides a new pore structure that is well suited for benzene molecules, and we denote it as a "shape-responsive fitting" transformation. This type of pore gives rise to a new guideline: frameworks can be composed of flexible motifs that are linked via strong bond and/or stiff motifs that are connected via weaker bonds.

We report the direct observation of dioxygen molecules physisorbed in the nanochannels of a microporous copper coordination polymer by the MEM (maximum entropy method)/Rietveld method, using in situ high-resolution synchrotron x-ray powder diffraction measurements. The obtained MEM electron density revealed that van der Waals dimers of physisorbed O 2 locate in the middle of nanochannels and form a one-dimensional ladder structure aligned to the host channel structure. The observed O–O stretching Raman band and magnetic susceptibilities are characteristic of the confined O 2 molecules in one-dimensional nanochannels of CPL-1 (coordination polymer 1 with pillared layer structure).

Faraday discovered the magnetism of molecular oxygen in 1850, and since then, oxygen has attracted significant interests as a ubiquitous but exotic molecular magnet. In solid oxygen, the magnetic energy through the exchange interaction is comparable to the van der Waals cohesive energy, resulting in a strong spin-lattice correlation. We reported the discovery of a magnetic-field-induced phase transition of solid oxygen using ultrahigh magnetic fields up to 186 T. This is the first experiments demonstrating the phase control through the spin by applying a magnetic field. Magneto-optical absorption measurements of the α phase at low temperatures revealed that visible light absorption suddenly ceases and the background transparency dramatically improves above the critical field. The large hysteresis in these data indicates a first-order transition with a relaxation time on the order of microseconds. The results strongly suggest the reconstruction of the O2 molecular geometry by the magnetic field, which causes that the antiferromagnetic phase collapses and the field-induced phase should have an isotropic crystal structure. Since all of the known phases of O2 are induced in high pressure, the discovery of a field-induced phase is noteworthy in the long history of solid O2 studies.

That the $4f$ electrons in the rare-earth antiferromagnetic compound ${\mathrm{CeRh}}_{2}{\mathrm{Si}}_{2}$ should be considered as localized electrons at cerium sites has been confirmed by comparing a de Haas--van Alphen experiment to the result of energy band calculations for ${\mathrm{LaRh}}_{2}{\mathrm{Si}}_{2}.$ When pressure p is applied to the compound, the N\'eel temperature ${T}_{\mathrm{N}1}=36 \mathrm{K}$ decreases and finally becomes zero at ${p}_{\mathrm{c}}\ensuremath{\simeq}1.0$--1.1 GPa. The topology of the Fermi surface is found to be almost unchanged up to 1.0 GPa, but the cyclotron effective mass increases with increasing pressure. Above 1.1 GPa, the topology of the Fermi surface changes abruptly. A new Fermi surface is explained by the $4f$-itinerant-band model. The corresponding cyclotron mass is large, being about ${22m}_{0}.$

High-energy spin excitations up to above 8000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ were measured by polarized Raman scattering in the insulating phases of S=1/2 copper oxides, ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$, ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.2}$, ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{0.5}$${\mathrm{Y}}_{0.5}$${\mathrm{Cu}}_{2}$${\mathrm{O}}_{8+\mathit{y}}$, ${\mathrm{Nd}}_{2}$${\mathrm{CuO}}_{4}$, and ${\mathrm{Pr}}_{2}$${\mathrm{CuO}}_{4}$, and an S=1 nickel oxide ${\mathrm{La}}_{2}$${\mathrm{NiO}}_{4}$. All the copper oxides commonly show anomalous spectra, especially the secondary scattering peaks near 4J (J is the two-spin superexchange energy). Those anomalies are caused by the large four-spin cyclic exchange interactions. The present experiments demonstrated that the four-spin exchanges show distinctive characteristics in cuprates as compared to other materials.

The spin excitations and the lattice vibrations in the insulator phase of the electronic superconductor Pr2CuO4 were investigated by wide-range Raman spectroscopy. The origin of the anomalous magnon spectra as in the case of the hole superconducting cuprates are assigned to the four-spin cyclic exchange interactions. The obtained two-spin superexchange integral J is 1040 cm−1. The phonon energies are 233 cm−1 in Alg, 287 cm−1 in Blg, and 165 and 474 cm−1 in Eg.

In a model system of an O2–O2 dimer confined in the nanopores of Cu-1,4-cyclohexanedicarboxylic acid, the molecular orientation associated with the spin state was observed by precise synchrotron radiation structure analysis. The obtained charge density level structures revealed that the molecular orientation varied with increasing temperature, coupling with the spin states of the O2–O2 dimer. The magnetic properties previously reported were consistently explained by the \(S = 1\) dimer model taking into account the molecular arrangements. The obtained gap parameters are different from those of the O2–O2 dimer confined in the nanopores of Cu-2,3-pyrazinedicarboxylate-pyrazine, which is explained by the pore deformation due to the adsorption, depending on the pore size and/or flexibility of the coordination polymer.

We have studied the superconducting properties of CeTIn 5 (T=Rh, Ir) under high pressures by means of electrical resistivity measurements and determined the pressure–temperature phase diagrams for the superconducting transition. For both systems, the superconductivity exists in a wide pressure range, 1.5⩽ P ⩽6.5 GPa for CeRhIn 5 and 0⩽ P ⩽5.2 GPa for CeIrIn 5 .

We have measured 63Cu-NQR spectral lines and nuclear spin-lattice relaxation time T1 under pressure up to 5.4 GPa. Daphne oil 7474 is used as the pressure-transmitting medium to obtain good hydrostaticity. NQR frequency 63νq above 4 GPa suddenly decreases from the linear pressure dependence in the low pressure range (P ≤ 3.5 GPa). The observed sudden downward deviation of 63νq is associated with an increase of Ce valence. Above 4.5 GPa, the linear pressure dependence of 63νq is observed again, most likely related to the sharp crossover to the high valence state.

Hall effect measurements were carried out under high pressures up to 4.9 GPa in a single crystal of CeCu2Si2. The temperature dependence of the Hall coefficient is interpreted to be composed of two peaks below room temperature. The high-temperature peak shows strong pressure dependence, where the peak shifts from 20 K at ambient pressure to 125 K at 4.9 GPa. This peak is a consequence of the anomalous Hall effect due to skew scattering. The low-temperature peak shifts from 5 K at ambient pressure to 15 K at 4.9 GPa and the magnitude of the peak shows the maximum around 4.1 GPa at which the superconducting transition temperature also reaches the maximum.

High-field magnetization measurements have been performed at various temperatures on the molecular oxygen adsorbed in a microporous coordination polymer CPL-1. Molecular oxygen with S = 1 forms O2-O2 dimer in the nanochannels of CPL-1. The magnetic properties can be explained by not the S = 1 Heisenberg antiferromagnetic dimer model but the O2-O2 dimer model taking into account the spin-dependent intermolecular potential. This feature is attributed to the fact that the magnetic interaction between O2 is comparable to the van der Waals force.