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Recent interest in topological nature in condensed matter physics has revealed the essential role of Berry curvature in anomalous Hall effect (AHE). However, since large Hall response originating from Berry curvature has been reported in quite limited materials, the detailed mechanism remains unclear at present. Here, we report the discovery of a large AHE triggered by a pressure-induced magnetic phase transition in elemental $\alpha$-Mn. The AHE is absent in the non-collinear antiferromagnetic phase at ambient pressure, whereas a large AHE is observed in the weak ferromagnetic phase under high pressure despite the small averaged moment of $\sim 0.02 \mu_B$/Mn. Our results indicate that the emergence of the AHE in $\alpha$-Mn is governed by the symmetry of the underlying magnetic structure, providing a direct evidence of a switch between a zero and non-zero contribution of the Berry curvature across the phase boundary. $\alpha$-Mn can be an elemental and tunable platform to reveal the role of Berry curvature in AHE.

Electrical resistivity and ac-susceptibility measurements under high pressure were carried out in high-quality single crystals of $\alpha$-Mn. The pressure-temperature phase diagram consists of an antiferromagnetic ordered phase (0, Comment: 6 pages, 4 figures

International audience; T he focus of much research on correlated-electron quantum materials is the competition between ordered and disordered electronic states, their tuning via quantum phase transitions and their possible relationship with unconventional superconductivity 1-6. Amongst these materials, URu 2 Si 2 occupies a special place, due to the richness of its quantum electronic properties and the challenge of understanding them 7. Discussions and controversies still exist about the nature of the 'hidden-order' (HO) phase, which is established below the temperature T 0 = 17.5 K. Efforts have been devoted to understand its order parameter, but so far none has been successful in determining it unambiguously. The transition at T 0 leads to strong physical responses, such as a large jump in the heat capacity 8 , an enhancement and a sudden gapping of intersite magnetic fluctuations 9,10 , a boost of the carrier mobility and a modification of the Fermi surface 11-14 and the opening of an electronic gap 15,16. While neutron diffraction experiments 17 showed a small antiferromagnetic (AF) moment below T 0 , most now accept that ambient-pressure antiferromagnetism is an extrinsic property induced by crystal defects and distortions 18. One proposal, motivated by Fermi-surface studies under pressure, is that the HO has the same periodicity of wavevector k 0 = (0 0 1) as the AF phase stabilized under pressure 19. The symmetry of the HO has also been considered: torque 20 and diffrac-tion 21 experiments lead to the proposal of a nematic behaviour in the HO phase. However, this picture faces a series of contradictory diffraction 22,23 , NMR 24 and thermodynamic 25 experiments, and the question of the symmetry remains open. Beyond experiments , many theories have tried to describe the HO within different approaches: localized, itinerant or dual (localized/itinerant) f-electrons, multipolar order, nematicity, spin liquid, 'hastatic' order and so on 26-30. It is difficult to find experimental evidence, in a direct and unambiguous manner, for the order parameters proposed by these models. To reveal the physics of the HO, an alternative route is to study how it can be destabilized by tuning external parameters 5. In the HO state, gapped low-energy magnetic fluctuations peaked at the wavevectors k 0 and k 1 = (0.6 0 0) (refs. 9,10) can be seen as precursors of long-range magnetic ordering with the same wavevectors and indicate nearby quantum phase transitions. In heavy-fermion paramagnets, such intersite magnetic fluctuations often indicate the proximity of a magnetically ordered phase. For instance, in the textbook CeRu 2 Si 2 case quantum magnetic fluctuations with wave-vector k 1 = (0.31 0 0) can be transformed into long-range magnetic order with the same wavevector by La doping 31. As well as doping, pressure and magnetic field are ideal tools to tune the electronic interactions. In URu 2 Si 2 , hydrostatic pressure 32-34 leads to a phase transition from the HO phase towards an AF state, with the wave-vector k 0 and the moments aligned along the c axis of the tetrago-nal crystal. At ambient pressure, under a magnetic field from 35 to 39 T applied along c, the HO is replaced by a spin-density wave (SDW), where the magnetic moments are ordered with the wave-vector k 1 and aligned along c (refs. 35,36). Remarkably, experiments under combined magnetic field and pressure, in the limited ranges 16 T/2 GPa (ref. 37) and 45 T/1 GPa (ref. 38), showed that a magnetic field applied to the pressure-induced AF phase induces a return to the HO phase 37 , and that the SDW phase shrinks and moves to higher fields under pressure 38. The relative stability of these different types of order is clearly complicated, and a full description of how URu 2 Si 2 evolves under combined pressure and magnetic field is needed. Here, we present the three-dimensional (3D) magnetic-field-pressure-temperature phase diagram of URu 2 Si 2. Its magnetoresis-tivity was measured in magnetic fields up to 60 T combined with pressures up to 4 GPa. We find a rich phase diagram indicating a subtle competition between the electronic interactions. The main features are the disappearance of the field-induced SDW phase and a squeezing out of the HO phase under high pressure. We emphasize that many of the boundaries of the 3D phase diagram are controlled by the field and pressure dependences of a single parameter characterizing the electronic correlations. The mystery of the hidden-order phase in the correlated electron paramagnet URu 2 Si 2 is still unsolved. To address this problem, one strategy is to search for clues in the subtle competition between this state and neighbouring magnetically ordered states. It is now well established that long-range antiferromagnetic order can be stabilized in this metal when it is under pressure and that a spin-density wave manifests when a magnetic field is applied along the easy magnetic axis c. However, the full boundaries of the hidden-order phase in the pressure-magnetic-field plane have not been determined so far. Here we present a systematic investigation of URu 2 Si 2 under combined high pressures and intense magnetic fields. The boundaries of the hidden-order, antiferromagnetic and spin-density-wave phases are mapped out, indicating an intricate three-dimensional phase diagram. We show that the field-induced spin-density-wave and hidden-order phases disappear in favour of antiferromagnetism at high pressure. Interestingly, a large number of phase boundaries are controlled by the field and pressure dependences of a single parameter. This gives new constraints for theories that model the electronic correlations and ordered phases in URu 2 Si 2. NAtURe PhySicS | VOL 16 | SEPTEMbER 2020 | 942-948 | www.nature.com/naturephysics 942

The field-angular dependence of Co-NMR spin-lattice relaxation rate 1/T1 has been measured for a 10% Co-doped single crystal of URhGe. The experiment revealed that spin fluctuations in ferromagnetic (FM) state of URhGe are robust against magnetic field below about 4 T, applied along any direction in the bc crystal plane. This is in clear contrast with the sister compound UCoGe, in which FM spin fluctuations are rapidly suppressed by a tiny applied field along the c axis. We show that such a difference in the character of the spin fluctuations is reflected in their two distinct phase diagrams for the upper critical field Hc2, providing further support to the mechanism of superconductivity mediated by spin fluctuations in these materials., 6 pages, 3 figures, accepted for publication in JPS Conference Proceedings

We have measured the temperature dependence of resistivity in single-crystalline CeNiGe$_{3}$ under hydrostatic pressure in order to establish the characteristic pressure-temperature phase diagram. The transition temperature to AFM-I phase $T_{\rm N1}$ = 5.5 K at ambient pressure initially increases with increasing pressure and has a maximum at $\sim$ 3.0 GPa. Above 2.3 GPa, a clear zero-resistivity is observed (SC-I phase) and this superconducting (SC) state coexists with AFM-I phase. The SC-I phase suddenly disappears at 3.7 GPa simultaneously with the appearance of an additional kink anomaly corresponding to the phase transition to AFM-II phase. The AFM-II phase is continuously suppressed with further increasing pressure and disappears at $\sim$ 6.5 GPa. In the narrow range near the critical pressure, an SC phase reappears (SC-II phase). A large initial slope of upper critical field $\mu_0H_{\rm c2}$ and non-Fermi liquid behavior indicate that the SC-II phase is mediated by antiferromagnetic fluctuations. On the other hand, the robust coexistence of the SC-I phase and AFM-I phase is unusual on the contrary to superconductivity near a quantum critical point on most of heavy-fermion compounds., Comment: 5 pages, 6 figures

Antiferromagnet Mn_{3}P with Neel temperature T_{N}=30 K is composed of Mn tetrahedrons and zigzag chains formed by three inequivalent Mn sites. Due to the nearly frustrated lattice with many short Mn-Mn bonds, competition of the exchange interactions is expected. We here investigate the magnetic structure and physical properties including pressure effect in single crystals of this material, and reveal a complex yet well-ordered helimagnetic structure. The itinerant character of this materials is strong, and the ordered state with small magnetic moments is easily suppressed under pressure, exhibiting a quantum critical point at ∼1.6 GPa. The remarkable mass renormalization, even in the ordered state, and an incoherent-coherent crossover in the low-temperature region, characterize an unusual electronic state in Mn_{3}P, which is most likely effected by the underlying frustration effect.

Potassium metal was loaded into K-form zeolite low-silica $\mathrm{X}$ $(\mathrm{LSX})$ under the loading pressure $P$ up to 1.5 GPa. A ferromagnetism is observed at $P\ensuremath{\approx}$ 0.9 GPa below 13 K. The loading density of K atom $n$ is estimated to be $\ensuremath{\approx}15$ per cage at the ferromagnetic loading pressure, and the pressure-derivative loading density $dn/dP$ has a remarkable peak $\ensuremath{\approx}11\phantom{\rule{4pt}{0ex}}{\mathrm{GPa}}^{\ensuremath{-}1}$ at $P\ensuremath{\approx}0.95$ GPa. The density of states at the Fermi energy is estimated to be $\ensuremath{\approx}46$ states/eV per cage from the value of $dn/dP$ on a simple model. The observed ferromagnetism is discussed in terms of the Stoner condition and the theory of the revised Rhodes-Wohlfarth plot.

We succeeded in growing single crystals of SrAl 4 and related compounds with the BaAl 4 -type tetragonal structure by the self-flux method, and measured the electrical resistivity, magnetic susceptibility, Hall coefficient, thermoelectric power, and de Haas–van Alphen (dHvA) effect. A plausible characteristic feature of the charge density wave (CDW) was observed below T CDW = 243 K in SrAl 4 . We also studied an effect of pressure on the electronic state in SrAl 4 by measuring the electrical resistivity and thermoelectric power. T CDW is found to decrease with increasing pressure, with a rate of dT CDW / dP = −12.5 K/GPa. To clarify the Fermi surface nesting, we studied the Fermi surface in SrAl 4 , which is found to be different from the Fermi surfaces of the similar compounds SrGa 4 , BaGa 4 , and BaAl 4 without CDW. The Fermi surfaces in these compounds were determined from the dHvA experiments, together with the energy band calculations.

Snake-like robots are useful for exploring narrow spaces such as in collapsed buildings after a severe disaster. Two people are usually required for operating serpentine robot, one for pushing and twisting, and the other for controlling the tip. In this paper, we propose a way to control a snake robot with a single operator, by the use of robotic thruster. Further, a robotic thruster has the advantage of improving the estimation of tip position and shape, by measuring the inserted length of the cable. In this study, the focus is on “ hairy ” robots, so called because an Active Scope Camera (ASC) is covered by inclined cilia acting as a self-propelling mechanism. When operating a snake robot, the most difficult challenge is to insert it without damaging the cilia. First, opposed flexible rollers are proposed to push the robot whose cylindrical surfaces are covered by tensed flexible wires. The wires sandwich the robotic body between the hairs to avoid damage. Then, by using the rollers, a thruster is proposed which can push and twist the ASC, and measure both the inserted length and twisting angles. Basic performance experiments showed that the thruster could successfully push and twist an ASC of approximately 5 m. The accuracy of the inserted length and twisting angle were less than 10% and 45%, respectively. The thruster was able to push and twist the ASC on flat environments with obstacles, and in a three-dimensional rubble environment.

We review our 59Co NMR study in a URhGe single crystal doped with 10% cobalt. The spin-spin relaxation time ( T 2 ) measurements have revealed a divergence of electronic spin fluctuations in the vicinity of a field-induced tricritical point (TCP) locating around 13 T. The fluctuations is developed in the same limited field region around the TCP as that where a reentrant superconductivity (RSC) is observed in URhGe. The finding strongly suggests these quantum fluctuations as the pairing glue responsible for the RSC.

Zeolite LSX (low-silica X) crystals have an aluminosilicate framework with regular supercages and β-cages. They are arrayed in a double diamond structure. The loading density of guest K atoms per supercage (or β cage), n, can be controlled from 0 to ≈ 9. At n 6. These properties are explained by the polaron effect including the electron correlation. Ferrimagnetic properties are observed at n ≈ 9. A remarkable increase in the resistivity is observed at very low temperatures at n ≈ 9, and is discussed in terms of the hypothesis of a Kondo insulator.

Alkali metal nanoclusters can be stabilized in the regular cages of zeolite crystals by the loading of guest alkali metals. Cages are connected by the sharing of windows of the framework, and arrayed in simple cubic, diamond and body centered cubic structures in zeolites A, X and sodalite, respectively. The s-electrons have the localized nature of nanoclusters with magnetic moments, and have mutual interactions through the windows of cages. They show exotic magnetism depending on the structure type of zeolites, the kind of alkali metals and the average loading density of alkali atoms per cage. In zeolite A, potassium clusters are formed in α-cages that have an inside diameter of 11 A. They exhibit ferromagnetic properties explained by the canted antiferromagnetism of the Mott insulator, where the 1p-like degenerate orbitals of clusters play an essential role in the magnetic properties. Na-K alloy clusters generated at supercages and β-cages of low-silica X (LSX) zeolite exhibit Neel’s N-type ferrimagnetism at specific loading densities of alkali metals. Alkali metal clusters in sodalite show the ideal Heisenberg antiferromagnetism of the Mott insulator.

The ferromagnetic superconductor URhGe has been known to exhibit an extremely large enhancement of the upper critical field when the field is confined and rotated in the $(ab)$ crystal plane. Our high-field $^{59}\mathrm{Co}$ NMR measurements on 10% Co-doped URhGe up to 30 T prove that this unconventional behavior of the superconductivity (SC) is associated with a strong anisotropy of field-dependent quantum fluctuations near a tricritical point. These fluctuations are rapidly suppressed by the field component along the $c$ axis, while being unaffected by any field component along the $a$ axis. The observed close interplay between the SC and quantum fluctuations strongly supports a pairing mechanism mediated by these fluctuations in URhGe.

The field-induced reentrant superconductivity (RSC) discovered near a quantum critical point (QCP) in a ferromagnetic superconductor URhGe highlights the close interplay between superconductivity and magnetism. While the origin of the RSC is broadly thought to be associated with quantum critical fluctuations, their exact nature had not been well identified. Here we review our recent 59Co NMR study in a single crystal of URh0.9Co0.1Ge. Our measurements of the NMR spin-spin relaxation reveal a divergence of electronic spin fluctuations in the vicinity of the field-induced QCP at HR ≈ 13 T. The fluctuations observed are characteristic of a tricritical point, followed by a phase bifurcation toward quantum wing-critical points. We show that these tricritical fluctuations enhance the effective mass of the conduction electrons and, further, drive the RSC near the HR.

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

Thin films of mesoporous lamellar nickel oxides and nanotube manganese oxides were electrochemically fabricated on indium tin oxide (ITO) glass using sodium n-dodecyl sulfate (SDS) as a template agent under different controlled potentials in 10 mM Ni(NO 3 ) 2 and 100 mM MnSO 4 solutions. Electrochromic characterization together with the morphological observation by transmission electron microscopy (TEM), structure analysis by X-ray diffraction (XRD) and electron diffraction (ED) was made. Nickel and manganese oxide films of nanostructures, compared with conventional structure ones, showed marked changes in optical transmittance and electric charge with regard to the electrochromic reactions in aqueous solution of 100 mM LiOH. However, in a non-aqueous γ-butyrolactone (GBL) solution of 100 mM Bis(trifluoromethane)sulfonimide lithium, the nickel oxide films did not show any notable electrochromic reactions, while the manganese oxide films of both nanostructure and conventional structure are electrochromically active and the effect of nanostructure on the electrochromic properties was remarkable.

In this article, we have developed pressure loading technique to extend the loading density of guest alkali metals in nanoporous crystals of zeolites. Zeolite crystals have solid framework and open regular nanospace. In the nanocages of zeolite crystals, s-electrons provided by the guest alkali metals occupy quantum electronic states of clusters successively. Under the pressure by the use of the pressure medium of alkali metals, we have observed significant change in the magnetic properties, indicating that the pressure loading increases loading densities which are closely related to the s-electron occupation at the quantum states of clusters.

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 studied the change of the Fermi surface properties in antiferromagnets CeIn 3 and CeRhIn 5 via the dHvA experiments under pressure. We found the abrupt change of the Fermi surface at the critical pressure P c , where the magnetic ordering state changes to the paramagnetic one. The change of the Fermi surface indicates that the 4f-electron character is changed from localized to itinerant in CeIn 3 and CeRhIn 5 at P c . Namely, the 4f-electron contributes to the volume of the Fermi surface above P c . Interestingly, the pressure-induced heavy fermion state with large effective mass was observed around P c , where the pressure-induced superconductivity appears. We also discuss the Fermi surface properties in the system without inversion symmetry in the crystal structure as in CePt 3 Si and CeTX 3 (T:Co, Ir, Rh, X:Si, Ge). The spin–orbit interaction due to the lack of inversion symmetry brings about a splitting of the Fermi surface, which is important for considering the formation of Cooper pair.

The mineral tetrahedrite Cu$_{12}$Sb$_{4}$S$_{13}$ exhibits a first-order metal--insulator transition (MIT) at $T_{\rm MI}$ = 85 K and ambient pressure. We measured the $^{63}$Cu-NMR at ambient pressure and the resistivity and magnetic susceptibility at high pressures. $^{63}$Cu-NMR results indicate a nonmagnetic insulating ground state in this compound. The MIT is monotonically suppressed by pressure and disappears at $\sim1.0$ GPa. Two other anomalies are observed in the resistivity measurements, and the pressure -- temperature phase diagram of Cu$_{12}$Sb$_{4}$S$_{13}$ is constructed., Comment: 5 pages, 7 figures

Metalladichalcogenolate cluster complexes [{CpCo(S2C6H4)}2Mo(CO)2] (Cp = eta(5)-C5H5) (3), [{CpCo(S2C6H4)}2W(CO)2] (4), [CpCo(S2C6H4)Fe(CO)3] (5), [CpCo(S2C6H4)Ru(CO)2(P(t)Bu3)] (6), [{CpCo(Se2C6H4)}2Mo(CO)2] (7), and [{CpCo(Se2C6H4)}(Se2C6H4)W(CO)2] (8) were synthesized by the reaction of [CpCo(E2C6H4)] (E = S, Se) with [M(CO)3(py)3] (M = Mo, W), [Fe(CO)5], or [Ru(CO)3(P(t)Bu3)2], and their crystal structures and physical properties were investigated. In the series of trinuclear group 6 metal-Co complexes, 3, 4, and 7 have similar structures, but the W-Se complex, 8, eliminates one cobalt atom and one cyclopentadienyl group from the sulfur analogue, 4, and does not satisfy the 18-electron rule. 1H NMR observation suggested that the CoW dinuclear complex 8 was generated via a trinuclear Co2W complex, with a structure comparable to 7. The trinuclear cluster complexes, 3, 4, and 7, undergo quasi-reversible two-step one-electron reduction, indicating the formation of mixed-valence complexes Co(III)M(0)Co(II) (M = Mo, W). The thermodynamic stability of the mixed-valence state increases in the order 4 < 3 < 7. In the dinuclear group 8 metal-Co complexes, 5 and 6, the CpCo(S2C6H4) moiety and the metal carbonyl moiety act as a Lewis acid character and a base character, respectively, as determined by their spectrochemical and redox properties. Complex 5 undergoes reversible two-step one-electron reduction, and an electron paramagnetic resonance (EPR) study indicates the stepwise reduction process from Co(III)Fe(0) to form Co(III)Fe(-I) and Co(II)Fe(-I).

We measured the pressure dependence of in-plane resistivity ${\ensuremath{\rho}}_{ab}$ in the recently discovered iron-based superconductor ${\mathrm{Ca}}_{10}({\mathrm{Ir}}_{4}{\mathrm{As}}_{8}){({\mathrm{Fe}}_{2\ensuremath{-}x}{\mathrm{Ir}}_{x}{\mathrm{As}}_{2})}_{5}$, which shows a unique structural phase transition in the absence of magnetic ordering, with a superconducting transition temperature ${T}_{\mathrm{c}}=16$ K and a structural phase transition temperature ${T}_{\mathrm{s}}\ensuremath{\simeq}100$ K at ambient pressure. ${T}_{\mathrm{c}}$ and ${T}_{\mathrm{s}}$ are suppressed on applying pressure and disappear at approximately 0.5 GPa, suggesting a relationship between superconductivity and structure. ${\mathrm{Ca}}_{10}({\mathrm{Ir}}_{4}{\mathrm{As}}_{8}){({\mathrm{Fe}}_{2\ensuremath{-}x}{\mathrm{Ir}}_{x}{\mathrm{As}}_{2})}_{5}$ is a rather rare example in which the superconductivity appears only in a low-temperature ordered phase. The fact that the change in the crystal structure is directly linked with superconductivity suggests that the crystal structure as well as magnetism are important factors governing superconductivity in iron pnictides.

We grew single crystals of PrCoIn 5 , PrRhIn 5 , and PrIrIn 5 with the tetragonal crystal structure and measured the electrical resistivity, specific heat, magnetic susceptibility, magnetization and de Haas–van Alphen effect. These Pr compounds reveal no magnetic ordering. The topology of the Fermi surfaces is the same as that of a non-4 f reference compound LaRhIn 5 . The cyclotron mass and/or the electronic specific heat coefficient are also approximately the same as those of LaRhIn 5 . The magnetic susceptibility and magnetization are anisotropic, reflecting the crystal structure, which are well explained by the tetragonal crystalline electric field scheme with the singlet ground state.

We report the discovery of new superconducting and novel magnetic phases in CeIn$_3$ on the verge of antiferromagnetism (AFM) under pressure ($P$) through the In-nuclear quadrupole resonance (NQR) measurements. We have found a $P$-induced phase separation of AFM and paramagnetism (PM) without any trace for a quantum phase transition in CeIn$_3$. A new type of superconductivity (SC) was found in $P=2.28-2.5$ GPa to coexist with AFM that is magnetically separated from PM where the heavy fermion SC takes place. We propose that the magnetic excitations such as spin-density fluctuations induced by the first-order magnetic phase transition might mediate attractive interaction to form Cooper pairs.

Magnetic excitations in a single crystal of heavy-fermion superconductor PrOs 4 Sb 12 have been studied by inelastic neutron scattering (INS) at low temperatures under high magnetic fields. The crystal field (CF) excitations at 0.7 meV observed in a previous INS study of a polycrystal sample were confirmed in this study on a single crystal. The observed excitations in the zero magnetic field soften around a wave vector (1,0,0), which is the modulation vector of the field-induced antiferro-quadrupolar ordering, suggesting the presence of quadrupolar instability. The observed field dependence of excitations is better reproduced in a singlet ground-state model rather than in a non-Kramers doublet ground-state model. In a high resolution experiment, furthermore, the change of the excitation spectra at (1,0,0) was observed on passing through the superconducting transition temperature, indicating that the excitation and the superconductivity are closely related in PrOs 4 Sb 12 .

Neutron scattering experiments have been carried out that reveal the magnetic excitation in the ferromagnet CeAgSb2. Crystalline electric field excitations were observed at 5.2 and 12.5 meV in the paramagnetic state, indicative of the localized nature of the Ce 4f electron. Our analysis concluded that |Jz = ±1/2 is the ground state, while the first and second excited levels are mainly due to |±3/2 and |±5/2, respectively. The observed ferromagnetic moment is in good agreement with the ground-state saturation moment, gJμBJz ~ 0.43 μB. The spin wave dispersion is interpreted using the anisotropic Heisenberg model with ferromagnetic exchange interaction up to seventh-nearest neighbours. The spontaneous moment along the c-axis decreases with increasing field perpendicular to the c-axis, and disappears at the critical field Hc, which corresponds to the anomaly which appeared in the magnetization curve.

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.

Neutron diffraction experiments on the heavy-fermion superconductor PrOs 4 Sb 12 revealed that a small antiferromagnetic moment, parallel to [010] ( y -direction), is induced in the field-induced phase ( H ∥ z ). The analysis, based on the Γ 1 singlet ground state crystal field model, shows that antiferro-order of O y z -type quadrupole moments of Pr ions is formed in the field-induced phase. This strongly suggests that the crystal field ground-state of Pr ions in PrOs 4 Sb 12 is the Γ 1 singlet and the quadrupolar ordering is induced due to level crossing with an excited state under a magnetic field.

The electronic state in UGe2 has been studied via the de Haas-van Alphen (dHvA) effect under hydrostatic pressure. The dHvA oscillation has been observed not only in the strongly polarized state (p pc). The observed Fermi surface, mass enhancement and scattering mechanism are highly different in these states.

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 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.

The pressure dependence of the superconducting transition temperature (Tc) and unit cell metrics of tetragonal (NH3)yCs0.4FeSe were investigated in high pressures up to 41 GPa. The Tc decreases with increasing pressure up to 13 GPa, which can be clearly correlated with the pressure dependence of c (or FeSe layer spacing). The Tcvs. c plot is compared with those of various (NH3)yMxFeSe (M: metal atoms) materials exhibiting different Tc and c, showing that the Tc is universally related to c. This behaviour means that a decrease in two-dimensionality lowers the Tc. No superconductivity was observed down to 4.3 K in (NH3)yCs0.4FeSe at 11 and 13 GPa. Surprisingly, superconductivity re-appeared rapidly above 13 GPa, with the Tc reaching 49 K at 21 GPa. The appearance of a new superconducting phase is not accompanied by a structural transition, as evidenced by pressure-dependent XRD. Furthermore, Tc slowly decreased with increasing pressure above 21 GPa and at 41 GPa superconductivity disappeared entirely at temperatures above 4.9 K. The observation of a double-dome superconducting phase may provide a hint for pursuing the superconducting coupling-mechanism of ammoniated/non-ammoniated metal-doped FeSe.

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 measured the specific heat, thermal expansion coefficient, magnetization, electrical resistivity, magnetoresistance and de Haas-van Alphen (dHvA) effect in PrSn 3 . The dense Kondo effect was confirmed from a negative magnetoresistance and the presence of heavy electrons with the cyclotron effective mass of 8–9 m 0 for the main Fermi surface. The magnetic phase diagram was also clarified by the high-field magnetization measurement.

We have studied the magnetic and Fermi surface properties in a ferromagnet UGa 2 . The electrical resistivity, elastic constant, thermal expansion coefficient, thermoelectric power, magnetic susceptibility and Hall coefficient indicate highly anisotropic properties, reflecting the hexagonal structure. The 5 f 2 - and 5 f 3 -CEF schemes, based on the localized 5 f -electron nature, are discussed to understand the magnetic susceptibility and magnetization data. We have also done the magnetoresistance and de Haas-van Alphen (dHvA) experiments to investigate the Fermi surface properties. Both data are very complicated, implying that the Fermi surface is a multiply-connected one. They are explained neither by the localized 5 f 2 - and 5 f 3 -core models nor by the spin-polarized 5 f -itinerant model. The cyclotron mass is, however, rather light, ranging from 0.17 to 6.2 m 0 , which is consistent with the electronic specific heat coefficient of 11 mJ/K 2 ·mol.

We have measured the ac magnetic susceptibility in various fields and thermal expansion of single crystals of the heavy fermion compound ${\mathrm{CeCu}}_{6}$ at temperatures down to $250\ensuremath{\mu}\mathrm{K}$. The susceptibility of ${\mathrm{CeCu}}_{6}$ shows a peak at about 2 mK and has a large anisotropy. We also detected an anomaly of thermal expansion at the same temperature. The observed behaviors of the susceptibility and the thermal expansion in ${\mathrm{CeCu}}_{6}$ indicate the occurrence of an antiferromagnetic order.

Potassium clusters arrayed in zeolite A are known to show ferromagnetic properties at low temperature. The origin of the spontaneous magnetization has been explained by a model of spin-canting in an antiferromagnetically ordered state. The direct information for the magnetic structure, however, has not been obtained so far. In the present work, we measure the neutron powder diffraction by using pulsed neutron source at KEK-KENS below and above the Curie temperature. No significant temperature-dependence was, however, obtained within the statistical errors, namely, magnetic scattering could not be detected separately. We also estimate the intensity of magnetic scattering by assuming some possible magnetic structures with considering the magnetic form factor of the cluster wave function. The intensity of magnetic scattering is estimated to be extremely weak and higher S/N of ∼104 or more is required to detect the magnetic scattering of this material.

We have carried out the de Haas-van Alphen (dHvA) experiments in a valence fluctuating compound CeNi. Forty seven dHvA branches are observed experimentally, which are mainly centered at the symmetrical axes. Most of the dHvA branches are approximately explained by the 4 f -itinerant band model. The cyclotron mass is in the range from 3.0 to 27 m 0 . Branch α, which has the largest cross-sectional area of the Fermi surface in the detected branches along the a -axis, has the cyclotron mass of 27 m 0 . This mass is five times larger than the corresponding band mass of 5.45 m 0 .

We studied systematically a series of the ternary compounds RRhIn 5 (R: rare earth) which were grown in the single crystalline form by means of the flux method. Most of these compounds order antiferromagnetically at low temperatures, except for R = Y, La, Pr and Yb. The observed temperature dependence of the specific heat and the anisotropic features in the magnetic susceptibility and magnetization have been analyzed on the basis of the crystalline electric field (CEF) model, and an interesting relationship between the anisotropic exchange interaction and the CEF effect is obtained for RRhIn 5 compounds.

The pressure-doping technique was developed for further loading of guest potassium metal into porous crystals of zeolite beyond the upper limit at ambient pressure. A doping pressure dependence of the magnetic property of potassium clusters in cages of zeolite A is measured up to 320 MPa. The Curie constant monotonically decreases with increase in the doping pressure and shows very small values above 250 MPa. The magnetic susceptibility at 2 K, however, gradually increases and has a peak at 200 MPa. Observed decrease in the Curie constant is explained by the increase in the loading density of potassium. Simultaneously, the increase in the magnetic susceptibility at 2 K is explained by the superparamagnetism of ferromagnetic domains. A possible mechanism of change in the magnetic properties is discussed.

We have grown single crystals of CeRh 2 Si 2 and LaRh 2 Si 2 , and measured the temperature dependence of the thermal expansion coefficient. The magnetic component of the thermal coefficient in CeRh 2 Si 2 has been analyzed on the basis of the crystalline electric field. We have also succeeded in observing the de Haas-van Alphen (dHvA) effect of CeRh 2 Si 2 . The detected dHvA branches are small in cross-section and are observed in a narrow angle region centered at the symmetrical axis, reflecting the multiply-connected Fermi surface.

We report the novel phase diagram of superconductivity (SC) and antiferromagnetism (AFM) in heavy-fermion (HF) pressure( P )-induced superconductors CeRhIn 5 and CeIn 5 through nuclear-quadrupole-resonance (NQR) measurements under P . The P -induced superconductivity in CeRhIn 5 coexists with AFM on a microscopic level in P =1.5–1.9 GPa. By contrast, in CeIn 3 , the P -induced phase separation of AFM and paramagnetism (PM) takes place without any trace of a quantum phase transition. The outstanding finding is that SC sets in at both the phases magnetically separated into AFM and PM in P =2.28–2.5 GPa.

We have grown single crystals of CeRh 2 Si 2 and LaRh 2 Si 2 by the Czochralski pulling method in a tetra-arc furnace. The electrical resistivity and magnetic susceptibility are highly anisotropic, reflecting the tetragonal crystal structure. A metamagnetic transition is found for the magnetic field along the [001] direction at 26 T.

We have studied the metamagnetism in PrCu2 via the magnetostriction. The metamagnetic transition accompanies a conversion between an easy and a hard axes in magnetization and also a huge magnetostriction. It is due to the magnetoelastic effect arising from the quadrupolar interaction, bringing about the rotation of the quadrupole moment.

We report the discovery of novel phases in CeIn3 on the verge of antiferromagnetism (AFM) through the In-nuclear quadrupole resonance (NQR) measurements. We have found that even though a pressure (P)-induced phase separation into AFM and paramagnetism (PM) takes place, a novel superconductivity (SC), which is induced without strong spin fluctuations, has been found to coexist with AFM on a microscopic level. We propose that the magnetic excitations such as spin-density fluctuations induced by the first-order magnetic phase transition might mediate attractive interaction to form Cooper pairs.

Alkali-metal-intercalated FeSe materials, (NH3)(y)M0.4FeSe (M: K, Rb, and Cs), have been synthesized using the liquid NH3 technique. (NH3)(y)Cs0.4FeSe shows a superconducting transition temperature (T-c) as high as 31.2 K, which is higher by 3.8 K than the T-c of nonammoniated Cs0.4FeSe. The T(c)s of (NH3)(y)K0.4FeSe and (NH3)(y)Rb0.4FeSe are almost the same as those of nonammoniated K0.4FeSe and Rb0.4FeSe. The T-c of (NH3)(y)Cs0.4FeSe shows a negative pressure dependence. A clear correlation between T-c and lattice constant c is found for ammoniated metal-intercalated FeSe materials, suggesting a correlation between Fermi-surface nesting and superconductivity.