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We report the observation of superconductivity with multiple magnetic ordering and Rashba-type spin-orbit coupling in a layered polar semimetal EuAuBi. Magnetic transition is observed at 4 K, followed by a superconducting transition at 2.2 K, which is sensitive to the crystal surface conditions. The upper critical field Hc2 of 9.8 T for the out-of-plane field is three times higher than that for the in-plane field, which can be associated with the two-dimensional structure or the surface state. On the basis of first-principles calculations, it is found that the characteristic Hc2 possibly reflects the anisotropic modification of the Fermi surface by the effective combination of Rashba-type spin splitting and Zeeman spin splitting enhanced by Eu moments., 12 pages, 5 figures

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

We performed $^{185/187}$Re nuclear quadrupole resonance (NQR) measurements under pressure to investigate the superconducting properties of noncentrosymmetric superconductor Cd$_{2}$Re$_{2}$O$_{7}$ under various crystal structures. The pressure dependence of superconducting transition temperature $T_{\rm c}$ determined through ac susceptibility measurements is consistent with the results of previous resistivity measurements [T. C. Kobayashi $et al$., J. Phys. Soc. Jpn. 80, 023715 (2011).]. Below 2.2 GPa, in the nuclear spin-lattice relaxation rate $1/T_{1}$, a clear coherence peak was observed just below $T_{\rm c}$, indicating conventional $s$-wave superconductivity. In contrast, the coherence peak disappears at 3.1 GPa, suggesting a change in superconducting symmetry to the $p$-wave dominant state against pressure., Comment: 5 pages, 5 figures

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 succeeded in observing the de Haas–van Alphen effect in PrOs 4 P 12 which shows no anomaly down to 50 mK in contrast to PrFe 4 P 12 and PrRu 4 P 12 . The Fermi surface (FS) topology is reasonably explained by the energy band structure calculation based on a full potential linearized augmented-plane-wave method within the local-density-approximation. Whereas the localized nature of 4 f -electrons, we have confirmed a highly enhanced cyclotron effective mass up to 18 m 0 in PrOs 4 P 12 , which is enhanced 3.8 times compared to that of LaOs 4 P 12 . No nesting property with q =(1,0,0) in the FS of PrOs 4 P 12 has been confirmed, which suggests both the 4 f -electron's contribution and the FS nesting property play the role for the phase transitions in PrFe 4 P 12 and PrRu 4 P 12 .

We have studied a change of the Fermi surface in an antiferromagnet CeIn 3 via the de Haas–van Alphen experiment under pressure up to 3 GPa. With increasing pressure P , the Neel temperature T N =10 K decreases and becomes zero at a critical pressure P c ≃2.6 GPa. In the pressure region P > P c , we have observed a large main Fermi surface named a , which indicates that the electronic state of 4 f electron in CeIn 3 changes from localized to itinerant at P c , as observed in the similar antiferromagnets CeRh 2 Si 2 and CeRhIn 5 . The cyclotron effective mass m c * of this main Fermi surface is extremely enhanced around P c : m c * ≃60 m 0 at 2.7 GPa for the magnetic field along the direction.

We report nuclear quadrupole resonance (NQR) measurement at ambient pressure and resistivity measurement under high pressure in the new heavy fermion (HF) compound SmOs 4 Sb 12 . The NQR spectrum and the nuclear spin–lattice relaxation rate (1/ T 1 ) clearly demonstrate the bulk nature of ferromagnetic ordering below T C ∼2 K. The temperature dependence of 1/ T 1 exhibits the characteristic behaviors of a Kondo lattice. The application of pressure decreases Kondo temperature and stabilizes the magnetic ordering, which is the same tendency as that found in some Yb-based compounds. The obtained phase diagram indicates SmOs 4 Sb 12 to be in the vicinity of its ferromagnetic critical point.

We have succeeded in growing a high-quality single crystal of an antiferromagnet UPdGa 5 by the Ga-flux method with the off-stoichiometric composition of U : Pd : Ga = 1 : 2 : 7.3. The Neel temperature T N = 30.5 K is found to increase with increasing the residual resistivity ratio (RRR) and becomes constant for a high-quality single crystal sample whose RRR is larger than 50. The electronic state has been investigated by the de Haas–van Alphen experiment, indicating the similar cylindrical Fermi surfaces as in an antiferromagnet UPtGa 5 . We have also studied the pressure effect by measuring the electrical resistivity. The Neel temperature decreases with increasing pressure and becomes zero at 3.1 GPa. The antiferromagnetic state is changed into the paramagnetic state above 3.1 GPa.

Pressure-induced superconductivity is found in UIr without inversion symmetry. The pressure–temperature phase diagram has been investigated by means of the electrical resistivity and magnetization ...

We present recent advances in the magnetism and superconductivity of rare earth and uranium compounds. Heavy fermions are formed on the basis of the competition between the RKKY interaction and the Kondo effect in these compounds. The application of pressure to these compounds is useful to control the electronic states in the antiferromagnets CeRh 2 Si 2 and CeRhIn 5 , and the ferromagnet UGe 2 . The quadrupole interaction or the quadrupole Kondo effect is found to be responsible for heavy fermions in PrFe 4 P 12 . A rich variety of superconducting properties are demonstrated: superconductivity of CeCoIn 5 and CeRhIn 5 in the vicinity of a quantum critical point, coexistence of ferromagnetism and superconductivity in UGe 2 , and superconductivity based on the quadrupole fluctuations in PrOs 4 Sb 12 , together with the relation between the superconducting transition temperature and the quasi-two dimensionality of the electronic states.

We have succeeded in growing a single crystal of CeNiIn 4 with the orthorhombic crystal structure by the In-flux method. CeNiIn 4 is found to order antiferromagnetically below 1.4 K, with a successive change of the magnetic structure below 0.75 K. The magnetic phase diagram was formed by the specific heat and magnetization measurements. The electronic specific heat coefficient is determined as 80 mJ/K 2 ·mol. From these experimental results it is concluded that CeNiIn 4 is a usual 4 f -localized compound.

A series of the ternary compounds CeTBi 2 (T: Ni, Cu and Ag) have been grown in the single crystalline form by means of the flux method. These compounds crystallize in the tetragonal crystal struct...

We have succeeded in growing a single crystal of CePtGe 2 with the orthorhombic crystal structure by the Bi-flux method. In order to investigate the anisotropic properties, the magnetic susceptibility, magnetization and electrical resistivity measurements have been performed along the principal axes. From these measurements, it is found that CePtGe 2 orders ferromagnetically below T C = 5.1 K, and the magnetic easy-axis corresponds to the a-axis. The anisotropic properties have been analyzed on the basis of the crystalline electric field model. We have also studied the pressure effect on the ferromagnetic ordering, and T C is found to increase with increasing pressure. However, T C smears out around 3.5 GPa and a new phase appears at higher pressures, where the transition temperature of the new phase also increases with increasing pressure.

The pressure dependence of transport properties in CeRhIn5 was studied up to 8.5 GPa by using a diamond-anvil cell. The electrical resistivity does not follow the T 2 -dependecne of a Fermi liquid nature under any pressure. In this non-Fermi liquid state, superconductivity was observed in a wide pressure range of 1:5 GPa

We performed the DC-magnetization and neutron scattering experiments under pressure {\it P} for a pressure-induced superconductor UGe$_2$. We found that the magnetic moment is enhanced at a characteristic temperature {\it T}$^{*}$ in the ferromagnetic state, where {\it T}$^{*}$ is smaller than a Curie temperature {\it T}$_{\rm C}$. This enhancement becomes remarkable in the vicinity of {\it P}$_{\rm C}^{*}$ = 1.20 GPa, where {\it T}$^{*}$ becomes 0 K and the superconducting transition temperature {\it T}$_{\rm SC}$ shows a maximum. The characteristic temperature {\it T}$^{*}$, which decreases with increasing pressure, also depends on the magnetic field., Comment: To be published in J.Phys.Soc.Jpn

Field-induced long-range ordering is investigated by heat capacity and high-field magnetization measurements in Haldane gap system Ni(C 5 H 14 N 2 ) 2 N 3 (ClO 4 ) (NDMAZ). In the high-field magnet...

Neutron scattering experiments were carried out in order to investigate the field-induced antiferromagnetic long-range order and spin dynamics for the new Haldane compounds Ni(C 5 H 14 N 2 ) 2 N 3 (ClO 4 ) (NDMAZ) and Ni(C 5 H 14 N 2 ) 2 N 3 (PF 6 ) (NDMAP). We observed the energy gaps corresponding to the excited triplet, Δ x = 1.61 meV, Δ y = 1.76 meV, Δ z = 3.2 meV for NDMAZ and Δ x = 0.48 meV, Δ y = 0.64 meV for NDMAP. The dispersion in NDMAZ was well explained by the theoretical curve with the intra-chain interaction J = 50 K. The field dependence of the gap energy below critical field ( H c ), was observed for NDMAZ and NDMAP as applying the field perpendicular to the chain direction. The field dependence of the excitation levels in NDMAZ was well explained by the fermionic field-theory treatment of the one-dimensional Heisenberg antiferromagnetic Hamiltonian with these gap energies and g -value, 2.3. In NDMAP, we found that the excitation peaks at Q = (0 0 0.5) became unobservably weak above H c . ...

We report 123 Sb nuclear quadrupole resonance (NQR) measurements of the filled skutterudite heavy-fermion superconductor PrOs 4 Sb 12 under high pressure. The temperature dependence of NQR frequency and spin–lattice relaxation rate 1/ T 1 indicate that the crystal electric field splitting Δ CEF between the ground state Γ 1 singlet and the first excited state Γ 4 (2) triplet decreases with increasing pressure. However, it is found Δ CEF and T c stay constant above P ∼2 GPa revealed by Sb-NQR up to P = 3.82 GPa for the first time. Remarkably, the temperature dependence of 1/ T 1 below T c = 1.55 K at P = 1.91 GPa shows no coherence peak just below T c and power-law behavior well below T c in contrast to the exponential decrease observed at P = 0. Present results indicate the superconductivity in PrOs 4 Sb 12 under pressure has nodes in the superconducting gap function.

From the 7 Li nuclear magnetic resonance (NMR) and specific heat measurements of LiNiO 2 , consisting of a spin-1/2 triangular lattice, it is demonstrated that the previously suggested spin-glass-like freezing below T s g =8 K, which is caused by defects of Li ions, is not the true ground state, but rather a quantum disordered state is realized without a spin gap. This state is characterized by power-law behavior of the temperature dependence of the specific heat below 0.5 K. A spin-liquid state with short-range ferromagnetic correlations is suggested from new insight into the frustration of orbital ordering for doubly degenerate e g shells in the triangular lattice.

Enhancement of superconducting transition temperature T c is confirmed at around 16 GPa in the pressure-induced superconductor CeCu 2 Ge 2 . The superconducting H c - T c phase diagrams at the low- T c and high- T c pressure regions indicates that the heavy quasi particles form the singlet Cooper pairs. At both low- T c and high- T c pressure regions, Fermi liquid behavior of ρ∼ A T 2 is observed only at low temperatures below 1 K in the normal state induced by the external field above H c 2 . At 21 GPa where the superconductivity disappears down to 50 mK, the temperature region following ρ∼ A T 2 increases drastically up to 40 K and the coefficient A decreases rapidly. These results indicate that the strongly correlated electrons are responsible essentially for the appearance of superconductivity in this system.

Anisotropic resistivity in UIr has been investigated under high pressure. A huge enhancement of residual resistivity was found under high pressure for the measuring current parallel to the [0 1 0] direction while any anomalies were not observed in the resistivity for [1 0 1 ]. The residual resistivity for [0 1 0] reduced to the original value in the pressure range where superconductivity appears. This anomalous behavior indicates that the ground state in the high-ρ 0 state is not simple ferromagnet and the application of pressure induces the first-order transition to slightly different electronic state.

We report the results of susceptibility and magnetization measurements on ferromagnetic-antiferromagnetic alternating chain compounds [Cu(TIM)]CuCl 4 (TIM=2,3,9,10-tetramethyl-1,3,8,10-tetraenecyclo-1,4,8,11-tetraazatetradecane) and (4-BzpipdH)CuCl 3 (4-BzpipdH=4-benzylpiperidinium). Magnetization curves of both compounds are compared to those calculated for an S =1 linear-chain Heisenberg antiferromagnet. From the fitting of susceptibility data to a numerical formula calculated for an S =1/2 ferromagnetic-antiferromagnetic alternating chain [Inog. Chem. 33 (1994) 5171], we have estimated the antiferromagnetic exchange constant J AF / k B =2.9 K, the ferromagnetic exchange constant | J F |/ k B =4.7 K and the g-value of the magnetic moment g =2.06 for the former and J AF / k B =8.8 K, | J F |/ k B =38.8 K and g =2.17 for the latter, which are different from the values reported previously.

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 temperature dependence of the Hall coefficient of CeIn3 under high pressure has been investigated. The absolute value of the Hall coefficient shows an anomalous increase below T* ∼ 80 K at ambient pressure. The increase in T* with increasing pressure is similar to the pressure dependence of the characteristic temperature where the resistivity reaches its maximum. The temperature variations below T* at various pressures are well scaled on a single curve that is the formula based on the two-fluid model. No effect of the antiferromagnetic fluctuations observed in CeTIn5 (T = Co, Rh, and Ir) is observed above 2 K even near the critical pressure where antiferromagnetic ordering disappears.

Heat capacity and susceptibility measurements are performed down to 70 mK under magnetic fields in the Haldane-gap antiferromagnet (CH 3 ) 4 NNi(NO 2 ) 3 (TMNIN). We have observed no magnetic long range order within our experimental range of the temperature down to 70 mK and the magnetic field up to 7 T. The heat capacity reflects the field dependence of the energy gap and show a broad anomaly above a critical field H C , which has been also observed in NENP. In the adiabatic magnetization measurement, the spin temperature shows a minimum around H C . These results are interpreted as increasing of the energy gap above H C which may suppress the expected long-range-ordering.

The magnetic properties of MOTMP 4-methacryloyloxy-2,2,6,6-tetramethyl-piperidin-1-oxyl are studied at tempratures below 1 K. The dominant magnetic coupling between the radicals is ferromagnetic. The one-dimensional behavior observed in the temperature dependence of susceptibility is consistent with previous result of heat capacity measurement in which the intrachain ferromagnetic interaction is estimated to be J / k =0.9 K. The susceptibility in the ordered state, however, shows spin-flip transition, which reveals antiferromagnetic long range order. From the analysis of ordering temperature T N and critical field H C , the interchain interactions are also estimated by the mean field theory.

Heat capacity measurements of the quasi one-dimensional S =1 antiferromagnet Ni(C 2 H 8 N 2 ) 2 NO 2 (ClO 4 ) are performed in static magnetic fields up to 13 T. Applying a magnetic field, a broad anomaly appears below 5 K, which reflects the gap energy between the nonmagnetic ground state singlet and the excited states. The field-dependence of the energy gap estimated from the measured heat capacities gives the critical field values close to those obtained in high-field-magnetization measurements and non-zero gap remaining at the critical field. Within our experimental range of temperature and magnetic field, we have not observed any sharp peaks corresponding to the expected three dimensional magnetic long range ordering.

The pressure–temperature–field phase diagram and quantum fluctuation effect were investigated in the itinerant ferromagnet U3P4 by resistivity, ac susceptibility, and Hall effect measurements under high pressure. The zero-temperature ferromagnetic-to-paramagnetic transition is located at Pc ∼ 4.0 GPa. The tricritical point exists at P* = 3.8 GPa and T* = 32 K, where the ferromagnetic transition changes from second- to first-order. As a quantum fluctuation effect, the low-temperature resistivity at Pc follows T5/3 dependence, which was theoretically described in the case of a three-dimensional ferromagnet. This result indicates that the ferromagnetic-to-paramagnetic transition at Pc may be considered as weakly first-order. Another critical behavior, the huge enhancement of ρ0 observed at Pc, cannot be interpreted as the ferromagnetic fluctuation effect. The Hall effect measurements suggest that the magnetic structure in the ordered state changes under high pressure.

We present detailed investigations on the effects of Ni substitution (x) on Ce(Cu1−xNix)2Si2 with x < 0.3, and a pressure (p) study for x = 0.04(2), 0.05(2), and 0.09(2) by resistivity measurements. The Cu–Ni substitution suppresses both antiferromagnetic fluctuations and superconductivity in CeCu2Si2, and leads to a dramatic crossover from the heavy-fermion (HF) regime to the intermediate-valence (IV) regime with progressive Ni doping. The crossover can be characterized by a marked increase in Kondo temperature evaluated from resistivity, specific heat, and susceptibility measurements. In high-pressure resistivity measurements, the Ni-doped system exhibits similar anomalies to those observed in CeCu2Si2, namely, T-linear dependence, an enhancement of residual resistivity, and a marked decrease in the A coefficient of the T2-resistivity. Furthermore, we observed an unexpected upturn anomaly in resistivity in the Ni-doped system under high pressure. By constructing the x–p phase diagram of Ce(Cu1−xNix)2Si2...

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.

Magnetic properties of quasi-one-dimensional organic/molecular ferromagnets MOTMP and MATMP and an antiferromagnet AOTMP are studied. All samples shows the long-range order at low temperatures below 1K due to the interchain interaction. The ordered states are well described as an typical antiferromagnet. In MATMP and AOTMP, the weak ferromagnetic behavior is also observed in the magnetic field along the spin easy axis just below T N .

EuGa4 and EuAl4 crystallize in the BaAl4-type tetragonal structure. The antiferromagnetic order was observed at 15 and 16.5K in EuGa4 and EuAl4, respectively.1,2) The magnetic susceptibilities in EuGa4 and EuAl4 well follow the Curie–Weiss law with effective moments of 7.97 and 8.02 B, respectively, which are consistent with the theoretical value of 7.94 B for a Eu-divalent electronic state.1,3) In the electrical resistivity and thermoelectric power measurements under pressure, a shoulderlike change was observed below about 100K at 1GPa in EuGa4. Moreover, a similar resistivity hump was observed below TCDW 1⁄4 140K at ambient pressure in EuAl4. The authors in Ref. 2 considered that this transition corresponds to the emergence of a charge density wave (CDW). In this study, we measured the magnetoresistance and Hall effect to clarify whether this is indeed based on CDW transition. Single crystals of EuAl4 were grown by the Al self-flux method. The transverse magnetoresistance and Hall resistivity were measured with an AC resistance bridge. The magnetic field H was applied along the [010] and [001] directions. The electrical current flow J was parallel to the [100] direction. Figure 1 shows a Kohler plot for the transverse magnetoresistance in the configurations of H k 1⁄2001 and J k 1⁄2100 . Kohler’s rule, i.e., = 1⁄2 ðHÞ ð0Þ = ð0Þ 1⁄4 fðH= ð0ÞÞ, holds when the temperature dependences of the scattering relaxation time are the same for all carriers. The = above 150K, namely, at 150, 160, and 200K, is well scaled on a single curve, which indicates that Kohler’s rule is satisfied above TCDW. On the other hand, the = below 140K deviates from Kohler’s rule, indicating that the carrier density and/or the scattering mechanism change below TCDW. In the two-band model, the transverse magnetoresistance and Hall resistivity are expressed as xx 1⁄4 ex hxð ey þ hyÞ þ ð exR 2 h þ hxReÞH ð ex þ hxÞð ey þ hyÞ þ ðRe þ RhÞH2 ; ð1Þ yx 1⁄4 ðRe hx hy þ Rh ex eyÞ þ ReRhðRe þ RhÞH 2 ð ex þ hxÞð ey þ hyÞ þ ðRe þ RhÞH2 H; ð2Þ where ei ( hi) and Re (Rh) are the resistivity along the i 1⁄4 xor y-direction and the Hall coefficient of the electron (hole) band, respectively.4) The Hall coefficient of each band is inversely proportional to the carrier density as Re 1⁄4 1=nee and Rh 1⁄4 1=nhe, where ne and nh are the electron and hole densities, respectively. The resistivity of each band is ei 1⁄4 1=ne eie ( hi 1⁄4 1=nh hie), where ei ( hi) is the mobility of the electron (hole). The transverse magnetoresistance increases quadratically, = H, for a compensated metal (ne 1⁄4 nh) at a high field limit (!c 1), whereas it tends to saturate for an uncompensated metal (ne 61⁄4 nh). Here, !c is the cyclotron frequency and is the scattering relaxation time. !c is roughly estimated using the relation = ð!c Þ2, which is obtained from the free-electron model. There is one EuAl4 unit in a body-centered tetragonal primitive cell. Considering that Eu is divalent, as proved by the magnetic susceptibility data,3) EuAl4 is a compensated metal with an even number of valence electrons. The experimentally obtained H-dependent magnetoresistance of up to = 2:5 10 2 (!c 0:16), shown as the solid curve in Fig. 1, reveals that EuAl4 is a compensated metal above TCDW. On the other hand, the = below TCDW gradually deviates at higher fields from the initial H dependence, as shown by the broken curve in Fig. 1 and the broken line in the inset of Fig. 1, at 100K. The deviation at 100K occurs at = 8 10 3 (!c 0:09). This behavior corresponds to the tendency toward saturation at higher fields, although the high field limit (!c 1) is not satisfied. Therefore, the transverse magnetoresistance indicates that EuAl4 is a compensated metal above TCDW and changes into an uncompensated metal below TCDW. The present experimental result and the hump of μ just below TCDW indicate that ne or nh starts to decrease below TCDW. Figure 2 shows the temperature dependence of the Hall coefficient RH determined at 0 T, shown by solid circles for H k 1⁄2010 and by solid squares for H k 1⁄2001 . The phase transitions at TCDW 1⁄4 140K and TN 1⁄4 14K are well observed. RH is temperature independent and negative above TCDW for both field directions. This means that the anomalous Hall coefficient, which is related to the magnetic susceptibility, is negligible in EuAl4. The negative RH for the compensated metal indicates e > h. The absolute value of RH increases with decreasing temperature below TCDW. The Hall resistivity is proportional to the magnetic field above TCDW, for example, at 200K, as shown in the inset of Fig. 2. On the other hand, the Hall resistivity gradually deviates downward from the linear field dependence with decreasing 0.06

The pressure dependence of the valence of Ce ions in CeCu2Si2 has been investigated by means of X-ray powder diffraction (XRPD) and nuclear quadrupole resonance (NQR) measurements. The high-pressure XRPD measurements were carried out at 12 K for CeCu2Si2 and CeCu2Ge2. Precise measurements under smoothly-applied pressure were achieved through the selection of the gasket material of a diamond anvil cell. The jump of the unit cell volume, which was reported previously in CeCu2Ge2, was not observed within the experimental accuracy, indicating the absence of a first-order valance transition. The pressure dependence of 63Cu-NQR frequency νQ measured in CeCu2Si2 was compared with that calculated from the measured lattice parameters. The νQ's were calculated for the two cases of LaCu2Si2 and CeCu2Si2, corresponding to localized and itinerant cases for \(4f\) electrons, respectively. The measured and calculated slopes dνQ/dP show good agreement. A small but significant deviation from the pressure-linear dependence...

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.

Pressure effects on the rattling and superconductivity in the Einstein solids; AxV2Al20 (Ax = Ga0.2, Al0.3, and Y) are investigated by means of electrical resistivity measurements under high pressure. We observed bumps in resistivity at low temperatures only for Ga0.2 and Al0.3, which can be explained by scattering of conduction electrons by local phonons with Einstein temperatures of 8.5 and 22 K, respectively. The bumps gradually fade out with increasing pressure, and the temperature variations of resistivity for Ga0.2 and Al0.3 approach those of Y. This indicates that the low-energy local phonons in the Ga and Al compounds disappear at high pressures. We also observed \(T^{2}\) behavior with large \(A\) coefficients in the low-temperature limit for Ga and Al compounds, but not for Y. With increasing pressure, the \(A\) coefficient is largely suppressed, while \(H_{\text{c2}}' \equiv |\mathrm{d}H_{\text{c2}}/\mathrm{d}T|_{T_{\text{c}}}\) that also reflects the density of states at Fermi energy decreases...

The superconductivity of Cd 2 Re 2 O 7 is investigated under hydrostatic pressures up to 4.6 GPa by means of electrical resistivity. A rich phase diagram is obtained, which contains at least five new pressure-induced phases in addition to the three already present at ambient pressure, revealing inherent structural and electronic instabilities of the compound. We find large enhancements of more than one order of magnitude in the upper critical field as well as in the coefficient of the T 2 term in resistivity at around a critical pressure of 4.2 GPa, where an inversion-symmetry-breaking structural transition tends to disappear. Heavy fermion superconductivity is probably realized under high pressures in Cd 2 Re 2 O 7 , which is extraordinary for d -electron compounds.

We report the results of Hall effect measurements on CeCu 2 Si 2 under high pressures up to 4.8 GPa. The Hall coefficient at ambient pressure increases with decreasing temperature and exhibits maximum at 4 K. The Hall coefficient at temperature higher than the coherent temperature of 10 K is consistent with the anomalous Hall effect. The pressure effect on the temperature dependence of the Hall coefficient is not simple. The pressure dependence of the Hall coefficient shows anomaly from 3.1 to 4.8 GPa, where the superconductivity is enhanced. These results indicate the close relationship between the Hall coefficient and the superconductivity.

Heat capacity and ac-susceptibility measurements under high pressure are carried out in SmOs 4 Sb 12 . Application of pressure increases the Curie temperature T C and enhances the heat-capacity jump at T C . On the other hand, the peak value of ac-susceptibility at T C decreases above 1 GPa and then almost vanishes at 3.6 GPa. These experimental facts suggest that the ordered state in SmOs 4 Sb 12 is not simple ferromagnetic state but possibly multipolar ordered state.

We report the results of 63 Cu nuclear quadrupole resonance (NQR) measurements on CeCu 2 Si 2 under high pressures up to 4.8 GPa. Enhanced spin fluctuations due to quantum criticality at ambient pressure 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. The nuclear spin–lattice relaxation rate 1/ T 1 at 4.2 GPa reveals that anisotropic superconductivity in the strong-coupling regime is realized even under high pressure far from the antiferromagnetic critical point. Superconductivity under high pressure is unconventional in origin, but the spin fluctuation scenario is not likely to be applicable.

Pressure-induced superconductivity is found in UIr without inversion symmetry. The pressure–temperature phase diagram has been investigated by means of the electrical resistivity, ac-susceptibility and magnetization measurements under high pressure. The phase diagram consists of three magnetic phases FM1–3 and a superconducting phase. The huge enhancement of residual resistivity and the negative magnetoresistance are found in the intermediate pressure region. These behavior may be induced by the pressure-induced structural phase transition and the accompanied phase separation in this pressure range. The superconducting phase with narrow pressure range is embedded in the FM3 phase, adjacent to zero-temperature FM3-to-nonmagnetic transition. The temperature dependence of resistivity above T SC follows non-Fermi liquid form of T 1.6 . From these experimental facts, superconductivity is considered to be associated with the ferromagnetic fluctuation.

We carried out the de Haas–van Alphen (dHvA) measurement and the pressure experiment of the electrical resistivity for an antiferromagnet Ce 3 Sn 7 with the orthorhombic crystal structure. The detected dHvA branches are many in number and their dHvA frequencies are extremely small in magnitude, indicating that Ce 3 Sn 7 is a semimetal. This is consistent with the result of the energy band calculations under the assumption that the 4 f electrons of two Ce atoms in the 2( a ) site are localized and the 4 f electron of one Ce atom in the 4( i ) site is itinerant. In the pressure experiment, the Neel temperature of T N = 5.3 K is found to slightly increase with increasing pressure, becomes maximum around 1 GPa, then decreases steeply with further increasing pressure and most likely becomes zero between 3 and 4 GPa. The antiferromagnetic state is changed into the non-magnetic state under pressure.

The antiferromagnet CeNiGe 3 exhibits superconductivity under pressure. The Neel temperature initially increases with increasing pressure up to 3 GPa and then becomes zero at a critical pressure ( ...

Heat capacities of high- T c superconductors Ba 2 RCu 3 O x (R=Gd, No, Er, Dy) aremeasured at temperatures below the respective superconducting transition temperatures. The observed sharp peaks at 2.25 K(Gd), 0.95 K(Dy), 0.55 K(Er) and 0.1 K(Ho) are associated with the magnetic ordering of the rare-earth ions in two dimensions. A co-existence of superconductivity and magnetic ordering is also confirmed down to the measured temperature of 30 mK.

In high- T c superconductors (La 1- x M x ) 2 CuO 4 (M=Ba, Sr), it has been reported that the heat capacity has a nonzero coefficient γ in the temperature linear term. We investigated the detailed dependence of γ on Ba doping. It was confirmed that γ becomes zero for undoped La 2 CuO 4 . With increasing Ba concentration x , γ increases markedly up to x =0.02 where the magnetic order almost disappears, while it decreases as superconductivity starts to appear and then has a minimum around x =0.04. With further increasing x , γ increases again. These results may be due to a combined effect of two different contributions to γ.