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We have succeed in growing single crystals of EuCu5 and EuAu5 with the hexagonal structure by the Bridgman method. Both compounds are known to be ferromagnets with Curie temperatures TC=57 ...

We report the results of muon spin relaxation ($\ensuremath{\mu}\mathrm{SR}$) and $^{29}\mathrm{Si}$ NMR measurements carried out on the cubic chiral magnet EuPtSi. This compound exhibits a helimagnetic transition at ${T}_{\mathrm{N}}=4$ K, and hosts a unique skyrmion phase characterized by a short modulation period and strong anisotropy under magnetic fields. Our zero-field $\ensuremath{\mu}\mathrm{SR}$ experiments revealed the development of critical slowing down of Eu spin fluctuations over a relatively wide critical region $(T\ensuremath{-}{T}_{\mathrm{N}})/{T}_{\mathrm{N}}l5$ above ${T}_{\mathrm{N}}$. We also found from $^{29}\mathrm{Si}$ NMR that the spin fluctuations are strongly suppressed by magnetic field in the paramagnetic state above 20 K. These characteristic spin dynamics observed over a wide region of temperature and magnetic field suggest the presence of magnetic frustration in the spin system. Such frustration would underlie the mechanism stabilizing the short-period skyrmion lattice observed in this compound.

We succeeded in growing single crystals of EuCuP with the hexagonal structure by the Sn-flux method and measured the electrical resistivity, specific heat, magnetic susceptibility, magnetization, thermal expansion, and Hall effect, together with the electrical resistivity under pressure and magnetic field. EuCuP is a ferromagnet with a Curie temperature T C = 32 K, following a divalent electronic state, although the temperature dependence of the electrical resistivity is not simple but possesses a sharp and distinct peak at T C . The Curie temperature is found to increase continuously with increasing pressure P, with a large rate of d T C / d P = 5.7 K/GPa up to 8 GPa. This means that the divalent electronic state is stable up to 8 GPa. The present resistivity peak at T C is, however, extremely suppressed by magnetic field, and is found to be characteristic in a ferromagnet with a small number of carriers, which was confirmed from a measurement of the Hall effect.

EuCo2Ge2 with the tetragonal structure is a Eu-divalent antiferromagnet with the Neel temperature T N = 23 K. The magnetic easy-axis corresponds to the [100] direction (a-axis), while the [001] direction (c-axis) is a hard-axis. The magnetization for H ∥ [ 100 ] indicates a metamagnetic transition at 25 kOe and saturates above 75 kOe. On the other hand, the hard-axis magnetization increases approximately linearly and saturates above 110 kOe. The magnetic phase diagram was constructed. A characteristic feature in EuCo2Ge2 is known as a valence transition under pressure, from Eu 2 + δ to Eu 3 − δ ′ ( δ , δ ′ 1 ). We also clarified the valence transition by measuring the electrical resistivity under pressure. The valence transition occurs at 3 GPa, with a hysteresis, and terminates at about 4.5 GPa. Further increasing pressure, the electronic state is changed into a moderate heavy fermion state and approaches the nearly trivalent electronic state.

Energetic materials such as a mixture of guanidine nitrate (GN)/basic copper nitrate (BCN) are used as gas generators in automotive airbag systems. However, at the time of the airbag inflation, the gas generators release toxic combustion gases such as CO, NH3, and NOx. In this study, we investigated the combustion and thermal decomposition behaviors of GN/BCN mixture, focusing primarily on their exhaust gas composition. As a result, when the exhaust gas of the combustion under constant pressure in an inert gas stream was analyzed using a detection tube, the amount of NOx (mainly NO) yielded greater decrease with increasing atmospheric pressure as compared to the amounts of CO and NH3. Thus, provided GN/BCN is ignited in a closed container, a large amount of NOx is presumed to have been released during the initial stage of combustion, which yielded comparatively low pressure. Results of the thermogravimetry–differential scanning calorimetry–Fourier transform infrared spectroscopy (TG/DSC/FTIR) indicated that the GN/BCN mixture caused endothermic decomposition at 170 °C and exothermic decomposition at 208 °C, which was accompanied by 66% mass loss. The decomposition gases, CO2, N2O, and H2O, were detected via FTIR spectrum. Because N2O was not detected in the combustion gas, it was suggested that the detected N2O was generated at a low temperature and decomposed in high-temperature combustion.

We succeeded in growing single crystals of SrTGe 3 (T: transition metal) by the In-flux method and measured the electrical resistivity, specific heat, and de Haas–van Alphen (dHvA) effect. We confirmed superconductivity in SrPdGe 3 and SrPtGe 3 , which was previously observed using polycrystal samples, and also found superconductivity for SrRhGe 3 , SrIrGe 3 , and SrNiGe 3 . Furthermore, from the results of dHvA experiments and energy band calculations, Fermi surfaces of SrIrGe 3 are found to split into two similar Fermi surfaces, reflecting the Rashba-type non-centrosymmetric tetragonal structure. We also grew single crystals of EuTGe 3 by the same In-flux method and studied magnetic properties, especially focusing on magnetism of EuIrGe 3 with a Neel temperature T N =12.2 K and a successive magnetic transition T ' N =7.3 K. The magnetic phase diagram of EuIrGe 3 is found to consist of three antiferromagnetic phases named AF1, AF2, and AF3. A critical field H c reaching a saturated moment of 7 μ B /Eu is determined as H c ≃ 160 kOe from a high-field magnetization curve. We proposed a simple helical magnetic structure based on the Dzyaloshinskii-Moriya interaction.

We succeeded in growing single crystals of \(\hbox {Yb}_{4}\hbox {Sb}_{3}\), Ullmannite(NiSbS)-type compounds, \(\hbox {Pd}_{3}\hbox {Bi}_{2}\hbox {Si}_{2}\), EuPtSi, and EuPtGe with the non-centrosymmetric cubic structures by the Bridgman method. Split Fermi surface properties are clarified for \(\hbox {Yb}_{4}\hbox {Sb}_{3}\) and \(\hbox {Pd}_{3}\hbox {Bi}_{2}\hbox {Si}_{2}\). As for EuPtSi and EuPtGe with the cubic chiral structure, we observed the first-order like antiferromagnetic ordering at the Neel temperatures \(T_N=4.0\,{\rm K}\) and 3.4 K, respectively, which are small in magnitude compared with ordering temperatures of 10–100 K in the usual divalent Eu compounds, reflecting the frustration of spins in the chiral structure.

We grew single crystals of EuCo2P2 and EuT2Ge2 (T: Co, Rh, Ir, Ni, and Pd) by the Bridgman method and Sn- and In-flux methods, and studied their magnetic properties by measuring the specific heat, ...

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.

We grew single crystals of EuCu2Si2 by the Bridgman and In-flux methods, and studied their crystallographic and magnetic properties precisely to clarify the ground state at low temperatures. The Br...

Most of the Eu compounds are in the divalent (Eu) electronic state and order magnetically. On the other hand, the Eu-trivalent (Eu) compounds exist but are small in number. An energy difference between the Eu and Eu states is, however, not extremely large. Therefore, the valence transition occurs in some Eu compounds. We present the characteristic properties of the Eu compounds from several viewpoints: a canting magnetisation in the Eu-antiferromagnets, the Fermi surface property in the Eu-compounds of EuPd and EuCoSi, the heavy fermion state in EuNiP, the temperature-induced valence transition in EuPdSi, the pressure-induced valence transition in EuRhSi and EuRuP, and the heavy fermion state approaching to the quantum critical point with increasing pressure in EuNiGe .

We measured the magnetization, ac susceptibility, Hall resistivity, and magnetoresistance for a cubic chiral antiferromagnet EuPtSi, and found the skyrmion lattice of the so-called “A-phase” in a w...

We report the results of 151Eu Mossbauer spectroscopy on EuPtSi with a chiral structure belonging to the P213 (#198) space group at zero magnetic field. The paramagnetic single absorption forms a m...

MnP is a prototype 3d-itinerant magnet but still a compound under considerable study. This is based on the characteristic magnetic phases including the helical, cone, and fan structures and a varie...

FeSn is an antiferromagnet with the Neel temperature TN = 370 K, while CoSn is a Pauli paramagnet. We grew high-quality single crystals of FeSn and CoSn with the hexagonal structure and mainly stud...

In this study, the electrical resistivity and magnetization of a single crystal of Ce2Ni3Ge5 heavy fermion compound were performed under pressure. The resistivity and magnetization showed two antiferromagnetic transitions at ambient pressure. On applying pressure, the transitions merged at 1 GPa. At higher pressures, the antiferromagnetic transition temperature decreases, and disappears. It is suggesting that the critical pressure of Ce2Ni3Ge5 was 4.1 GPa.

The effects of a magnetic field and pressure on the Kondo-like behavior in the valence-fluctuating antiferromagnetic compound EuPt2Si2 were studied using single-crystalline samples. The logarithmic...

EuPtSi crystallizes in the cubic chiral structure (P213, No. 198), which is the same as the non-centrosymmetric space group of MnSi with the skyrmion structure, and orders antiferromagnetically below a Neel temperature TN = 4.05 K. The magnetization at 2 K for the [111] direction indicates two metamagnetic transitions at the magnetic fields HA1 = 9.2 kOe and HA2 = 13.8 kOe and saturates above Hc = 26.6 kOe. The present magnetic phase between HA1 and HA2 is most likely closed in the \((H,T)\) phase and is observed in a wide temperature range from 3.6 to 0.5 K. In this magnetic phase known as the A-phase, we found giant additional Hall resistivity ΔρH(H) and magnetoresistance Δρ(H), reaching ΔρH(H) = 0.12 µΩ·cm and Δρ(H) = 1.4 µΩ·cm, respectively. These findings are obtained for H || [111] and [100], but not for H || [110] and [112], revealing an anisotropic behavior in the new material EuPtSi.

We report pressure-induced superconductivity in antiferromagnetic cerium compounds and a ferromagnetic uranium compound, focusing on the relation between the superconducting state and the Fermi surface instability in CeRhIn5 and the huge upper critical eld Hc2 in CeIrSi3 without inversion symmetry in the crystal structure. The pairing interaction is well correlated with ferromagnetism, as well as antiferromagnetism or antiferromagnetic uctuations. In the recently discovered superconductor NpPd5Al2, superconductivity is found to be located in the vicinity of an antiferromagnetically ordered state. The upper critical eld Hc2 is strongly supressed by the large paramagneic e ect, and the corresponding magnetization curve indicates a step-like increase at Hc2, producing a rst-order phase transition.

Single crystals of a pressure-induced superconductor Ce 2 Ni 3 Ge 5 have been successfully grown by the flux method. The anisotropic magnetic properties due to the orthorhombic crystal structure have been studied precisely by the electrical resistivity, specific heat, magnetic susceptibility, and high-field magnetization measurements. The results of these measurements confirmed two antiferromagnetic transitions at T N1 =5.0 K and T N2 =4.3 K. The electronic specific heat coefficient obtained from the low-temperature specific heat data amounts to 90 mJ/K 2 ·mol Ce. The high-field magnetization for H ∥[100] shows four magnetic transitions at 11.8, 12.9, 17.5 and 23.9 T with a saturation moment of 0.73 µ B /Ce at 1.3 K. On the other hand, two magnetic transitions are observed for H ∥[010] and [001], with saturation moments of 0.43 and 1.1 µ B /Ce, respectively. We have also performed the crystalline electric field (CEF) analysis on the magnetic susceptibility and magnetization to understand the magnetocrysta...

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.

We measured the electrical resistivity of an antiferromagnet Ce2Ni3Ge5 with the orthorhombic crystal structure under pressure. The Neel temperature TN = 5.2 K decreases with increasing pressure P and becomes zero at a critical GPa. The A and ρ0 values of the low-temperature electrical resistivity ρ = ρ0+AT2 in the Fermi liquid relation increase steeply above 3 GPa. A value of A = 10.7 µΩ cm K−2 at 3.9 GPa iscomparable to A = 10 µΩ cm K−2 in a heavyfermion superconductor CeCu2Si2. The heavy fermion state was found to be formed around Pc, in which pressure region superconductivity was found below 0.26 K.

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.

We carried out a de Haas–van Alphen (dHvA) experiment under pressure on a heavy-fermion superconductor, URu2Si2. The dHvA frequency, which corresponds to a nearly spherical Fermi surface, increases slightly with increasing pressure, while the corresponding cyclotron mass decreases considerably. Neither the dHvA frequency nor the cyclotron mass exhibit any abrupt change at the critical pressure of 1.5 GPa. The present result is thus inconsistent with a recent phase-separation proposal.

We studied the electronic states of two antiferromagnets, UPtGa 5 and UN, by measuring the electrical resistivity under pressure. When pressure P is applied, the Neel temperature T N decreases, becoming zero at P c = 8.0 GPa for UPtGa 5 and P c = 3.5 GPa for UN.

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.

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.

We succeeded in growing high-quality single crystals of pyrite-type cubic compounds CoSe2 and CoS2 using a transport agent of CoBr2 and measured the electrical resistivity, specific heat, magnetic susceptibility, magnetization, and the de Haas–van Alphen (dHvA) effect. We confirmed that CoSe2 is an exchange-enhanced paramagnet revealing a broad maximum at around 50 K in the temperature dependence of the magnetic susceptibility. The electronic specific heat coefficient is moderately large, γ = 18 mJ/(K2mol). On the other hand, CoS2 is a ferromagnet with a Curie temperature T C = 122 K and an ordered moment μ s = 0.93 μB/Co. The γ value of 21 mJ/(K2mol) in CoS2 is slightly larger than that of CoSe2. A large ordered moment, together with a large γ value, is a characteristic feature in CoS2 because CoS2 is a half-metallic spin state in the ferromagnetic state. Correspondingly, we detected a main dHvA branch with a large cyclotron effective mass of 13m 0 in the dHvA experiments. The detected dHvA branches in CoS2 and CoSe2 are discussed on the basis of the results of energy band calculations, revealing a broken four-fold-symmetry in the angular dependence of the dHvA frequency.

We studied the magnetic properties of the antiferromagnets Eu2Ni3Ge5 and EuRhSi3 by measuring their electrical resistivity, specific heat, magnetic susceptibility, magnetization, and thermoelectric power, together with the electrical resistivities at high pressures of up to 15 GPa. These compounds have almost divalent Eu ions at ambient pressure and order antiferromagnetically with a successive change in the antiferromagnetic structure at TN = 19 K and \(T'_{\text{N}} = 17\) K in Eu2Ni3Ge5, and at TN = 49 K and \(T'_{\text{N}} = 45\) K in EuRhSi3. Magnetic field versus temperature (H–T) phase diagrams were constructed for both compounds from the magnetization measurements. The Neel temperature in Eu2Ni3Ge5 was found to increase up to 7 GPa but to decrease continuously with further increasing pressure, without the so-called valence transition. Under a high pressure of 15 GPa, Kondo-like behavior of the electrical resistivity was observed, suggesting the existence of the heavy-fermion state at low temperatu...

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 low-temperature specific heat in magnetic fields up to 80 kOe, together with the magnetization for the heavy-fermion superconductor CeCoIn 5 with the transition temperature T c = 2....