Search

We present evidence for the quasi one-dimensional (1D) antiferromagnetism of CuO in the framework of the Heisenberg model. Our result supports the speculations and conclusions made by earlier authors. We also present experimental evidence which explains the reason for CuO to be a quasi 1D antiferromagnet in spite of appearing to have a 3D structure.

We report the pressure effects on lattice constants, magnetic susceptibility, specific heat and electrical resistivity in the orthorhombic PrCu 2 . Anisotropic compression is realized to be κ a ≈κ c

The Ni–Cr–Al Russian alloy was prepared. Its magnetic and mechanical properties were better than those of MP35N alloy. We fabricated the a piston–cylinder-type hybrid high-pressure cell using the Ni–Cr–Al alloy. It has been found that the maximum working pressure can be repeatedly raised to 3.5 GPa at T = 2 K without any difficulties.

We report measurements of ac magnetic susceptibility ${\ensuremath{\chi}}_{\text{ac}}$ and de Haas--van Alphen (dHvA) oscillations in ${\mathrm{KFe}}_{2}$${\mathrm{As}}_{2}$ under high pressure up to 24.7 kbar. The pressure dependence of the superconducting transition temperature ${T}_{c}$ changes from negative to positive across ${P}_{c}\ensuremath{\sim}18$ kbar, as previously reported. The ratio of the upper critical field to ${T}_{c}$, i.e., ${B}_{c2}/{T}_{c}$, is enhanced above ${P}_{c}$, and the shape of the ${\ensuremath{\chi}}_{\text{ac}}$ versus field curves qualitatively changes across ${P}_{c}$. dHvA oscillations smoothly evolve across ${P}_{c}$, indicating no drastic change in the Fermi surface up to 24.7 kbar. Three dimensionality increases with pressure, while effective masses show decreasing trends. We suggest a crossover from a nodal to a full-gap $s$ wave as a possible explanation.

Magnetic susceptibility and electrical resistivity in the metal–insulator (MI) transition of a mixed-valent Ti-oxide system, Y 1− x Ca x TiO 3 , are investigated at high pressure. This system exhibits obviously the first-order temperature-induced MI transition at x =0.35–0.4. In the low temperature metallic phase, susceptibility, χ ( T ), is strongly suppressed with pressure. On the other hand, in the high temperature semiconductiong phase χ ( T ) obeying the Curie–Weiss law is affected weakly by applying pressure. Below the MI transition temperature resistivity, ρ ( T ), shows the characteristic Fermi liquid behavior, ρ = ρ 0 + AT 2 . The coefficient of the T 2 -term in resistivity, A , and the residual resistivity, ρ 0 , decrease rapidly with pressure, while following the simple relation of A(x, P)∝ρ 0 (x, P) . A scaled temperature-composition phase diagram shows that the first-order transition terminates at both the lower and upper critical points and A , ρ 0 and χ are enhanced enormously at the lower critical point. We present scalings between susceptibility and resistivity in the metallic state taken into account the distribution of the Kondo temperature.

Cu(Ir12xRhx) 2S4. The features of the M2I transition change with Rh concentration x. A phase diagram of temperature versus x will be proposed for the Cu(Ir12xRhx) 2S4 system. The sharp M2I transition temperature varies drastically from 226 to 93 K with x from 0.00 to 0.17 and disappears around x50.20. In a region of 0.00

The thiospinel CuIr2S4 exhibits a temperature-induced metal-insulator (M -I) transition around 226 K, showing hysteresis on heating and cooling, that manifests itself as a gap in the electronic density of state with increasing electrical resistivity at low temperatures. Conversely, CuIr2Se4 remains metallic down to 0.5 K. We have successfully synthesized the spinel-type compound CuIr2(S12xSex)4 system. In order to see the effect of substitutions of Se at the S sites, we have carried out a systematic experimental study of structural, electrical, and magnetic properties of CuIr2(S12xSex)4 . Mossbauer spectroscopy measurements of Ir have been performed for CuIr2S4 and CuIr2Se4 . The M -I transition of CuIr2(S12xSex)4 for x 0.80. Magnetic susceptibility measurements show the jump at the M -I transition temperature with hysteresis on heating and cooling. The high-temperature metallic phase of CuIr2S4 shows Pauli paramagnetism, having a density of states at the Fermi level, D(eF)50.67 states/eV atom. The insulating phase at low temperatures exhibits diamagnetism, and there is no localized magnetic moment. The Arrhenius regime is observed for the conductivity with a thermally activated process for 0

Both (Y1−xPrx)Ba2Cu4O8 (hereafter abbreviated as Y/Pr124) and (Y1−xPrx)2Ba4Cu7O15−y (Y/Pr247) compounds were successfully synthesized over the whole concentration range 0≤x≤1 by means of either hot isostatic pressing (HIP) technique or high pressure oxygen gas technique. We revealed that the superconducting transition temperature disappears at xc=0.8 in both systems in contrast to xc=0.5 for the (Y1−xPrx)Ba2Cu3O7 (Y/Pr123) system reported in the literature and concluded from this that the suppression of superconductivity due to the Pr-doping is weaker in both 124 and 247 systems than that in the 123 system. Furthermore, a combination of the magnetic susceptibility data in the normal state with the Pr–O distance derived from the neutron diffraction experiments led us to conclude that the Pr ion is in the trivalent state for all samples in both 124 and 247 systems. An increase in the critical concentration xc in the Y/Pr124 and Y/Pr247 systems relative to that for the Y/Pr123 system is attributed to an increase in the hybridization of the Pr-4f and O-2p orbitals.

Pressure dependence of magnetization in CeP is investigated up to 2 GPa. Multi-step transitions are induced by pressure. An antiferromagnetic transition at TN = 11 K below 0.1 GPa develops into two (magnetic) transitions at TL and TH in the region of 0.1

The pressure dependence of the 100 K spin-state transition in LaCoO 3 is investigated through magnetization measurement under pressures of up to 18.2 kbar. The energy gap, Δ, between the low-spin ground state and the excited magnetic state (intermediate spin) increases remarkably with increasing pressure. The linear part of the pressure dependence of Δ, which is dominant below 5 kbar, is interpreted consistently by the volume expansion due to the spin-state transition under ambient pressure. In the higher pressure region, a quadratic pressure dependence is dominant, which suggests a very steep volume dependence of the energy of the excited magnetic state under the highly compressed condition.

The pressure induced semiconductor to metal transition in the rare earth compound TmTe has been investigated with electrical resistivity measurements under high pressure. At room temperature, the resistivity showed an exponential decrease up to 2GPa, indicating a linear closing of the energy gap, followed by an almost pressure independent metallic regime. The resistivity in the metallic regime showed a logarithmic temperature dependence reminiscent of a Kondo effect and a TmSe-like anomaly appeared at low temperature and above 5GPa. At 5.7GPa the resistivity showed an abrupt decrease that corresponded to the structural phase transition. {copyright} {ital 1997} {ital The American Physical Society}

A new strontium vanadium sulfide, SrV 2 S 5 , has been successfully synthesized. The powder X-ray diffraction pattern has been indexed on the basis of a rhombohedral cell with hexagonal lattice constants of a = 3.314 and c = 35.023 A. However, the electron diffraction measurements show that the structure is more complex and has an unidentified superstructure. The specimens of SrV 2 S 5 show no indication of superconductivity down to 2 K. The resistivity is low, semiconductive, and weakly dependent on temperature above 50 K. The magnetic susceptibility is nearly temperature independent above ∼80 K; below 50 K it shows extremely small Curie–Weiss-like behavior. Temperature dependence of the Knight shift in vanadium NMR shows a broad peak around 80 K.

The pressure-induced valence state of the Tm ions in TmTe has been investigated by means of X-ray diffraction and magnetic susceptibility measurements at high pressures. Below 2 GPa, the valence of Tm is conformed to be 2+ from the results of compressibility and magnetic susceptibility. In the pressure range from 2 GPa to 6 GPa, a valence transition from 2+ to 3+ is concluded from the pressure dependence of the lattice parameters observed by in situ X-ray diffraction. The NaCl-type structure with Tm in trivalent state, which appears above 6 GPa, is also shown to begin to transform to a tetragonal structure above 8 GPa by X-ray diffractometry.

The Mossbauer spectra of LaSrYCu 1.97 57 Fe 0.03 O 6 were measured from room temperature to 5K. Room temperature spectrum is a paramagnetic doublet, and IS and QS values suggest that high spin Fe 3+ are in octahedral site provided by a excess oxygen, similar to La 2 SrCu 2 O 6 . Below 210K, Mossbauer spectra become broad, and consist of paramagnetic doublet and magnetic sextet in the wide temperature range. Temperature variation of H hf suggest that the Neel temperature lies above 200K. The irreversibility and field dependence of susceptibility are observed at low temperatures. By combining the results of the Mossbauer spectra and magnetic measurements, these behaviors are explained as superparamgnetism of the antiferro spin clusters, and at low temperatures, clusters freeze to the cluster glass like state.

The magnetic susceptibility of α- and γ-Ce has been studied under high pressure up to 1.2 GPa. The magnetic susceptibility of γ-Ce obeys the Curie-Weiss law and the paramagnetic Curie temperature is considerably increased with increasing pressure. On the other hand, the susceptibility of α-Ce is nearly temperature independent at higher pressure. This behavior can be analyzed by use of the single impurity Kondo model giving the Kondo temperature as a function of volume. At ambient pressure, the Kondo temperatures are 25 K and about 1000 K in γ- and α-Ce, respectively.

Crystal structure and magnetic susceptibility were investigated for a thiospinel compound CuIr 2 S 4 , which exhibits a transition from metallic to insulating on cooling at the transition temperature T c of 230 K. It was found that the transition is accompanied by a first-order structural transition. As the compound is cooled through T c , the structure transforms from cubic to tetragonal with a volume contraction of 0.7%. The tetragonal phase has an axial ratio of about 1.03. Magnetic susceptibility, which is paramagnetic in the metallic region, decreases sharply and becomes diamagnetic at T c on cooling. The susceptibility is mostly temperature independent in each region above and below T c . Magnetic measurements also revealed that high pressure stabilizes the insulating phase, in contrast with most of the compounds that exhibit metal-insulator transitions. Possible mechanisms of the metal-insulator transition are discussed.

We have measured the temperature dependence of the electrical resistivity for an as-grown Gd 1.92 Ce 0.08 CuO 4 single crystal at pressures up to 1.6 GPa. Several resistivity anomalies were observed. We show that most of the anomalies well correspond with the magnetic transitions which have been observed in the magnetic susceptibility measurements. We have investigated the pressure dependence of those magnetic transitions. We also report the pressure dependence of the Neel temperature of Cu spins which is defined at the maximum of the derivation of the resistivity with temperature.

Pressure dependence of magnetic susceptibilities of YFe 2 O 4 and ErFe 2 O 4 has been measured up to 6 kbar above about 100 K. Two magnetic phase transitions are observed in the temperature region of 200–250 K at ambient pressure for both compounds. The transitions of YFe 2 O 4 are depressed with increasing pressure. Especially the lower transition rapidly decreases in temperature and then disappears at 6 kbar. The transitions of ErFe 2 O 4 show different pressure dependence, that is, the higher transition temperature increases and the lower one decreases with increasing pressure. The depression of the transition temperatures is explained as the volume effect on the first order phase transition, while the pressure dependence of the higher transition in ErFe 2 O 4 is interpreted as the 10/3 law for the volume dependence of superexchange interaction.

We report the ac magnetic susceptibility $\chi_{ac}$ and resistivity $\rho$ measurements of EuFe$_2$As$_2$ under high pressure $P$. By observing nearly 100% superconducting shielding and zero resistivity at $P$ = 28 kbar, we establish that $P$-induced superconductivity occurs at $T_c \sim$~30 K in EuFe$_2$As$_2$. $\rho$ shows an anomalous nearly linear temperature dependence from room temperature down to $T_c$ at the same $P$. $\chi_{ac}$ indicates that an antiferromagnetic order of Eu$^{2+}$ moments with $T_N \sim$~20 K persists in the superconducting phase. The temperature dependence of the upper critical field is also determined., Comment: To appear in J. Phys. Soc. Jpn., Vol. 78 No. 8

The thiospinel compound CuIr 2 S 4 exhibits the metal-insulator (M-I) transition accompanied by the structural transition. In this work, compounds of Cu 1- x Zn x Ir 2 S 4 in the composition range ...

Neutron scattering experiments and magnetic-susceptibility measurements have been performed to investigate the structural and magnetic properties of ${\mathrm{YBa}}_{2}$(${\mathrm{Cu}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Fe}}_{\mathit{x}}$${)}_{3}$${\mathrm{O}}_{7+\mathit{y}}$ with x=0.05, 0.10 (superconductors), and 0.15 (nonsuperconductor). Rietveld refinements of neutron diffraction at room temperature indicate that the Fe atoms occupy both the Cu(1) ``chain'' and Cu(2) ``plane'' sites---the occupation of the Cu(2) sites is about 30% of the total Fe content. Neutron-diffraction measurements down to 5.5 K indicate no evidence of long-range magnetic order; however, neutron small-angle scattering as a function of temperature shows a cusplike anomaly around 20 K. This suggests that the Fe-doped ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ system undergoes spin-glass ordering at low temperatures; accordingly, in the superconducting samples superconductivity and spin-glass coexist. Magnetic susceptibility for the nonsuperconducting sample gives further evidence for the spin-glass order. The results obtained are discussed in connection with the superconducting properties of this system.

We report measurements of the ac magnetic susceptibility and de Haas--van Alphen effect (dHvA) in $\mathrm{Ce}\mathrm{Rh}{\mathrm{Si}}_{3}$ up to a pressure $P=29.5\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$ with the field in the $c$ direction. The observed Fermi surface suggests that $\mathrm{Ce}\phantom{\rule{0.2em}{0ex}}4f$ electrons are itinerant even when antiferromagnetic order occurs. Effective masses decrease with $P$: no enhancement is observed as the antiferromagnetic transition temperature is reduced by the application of pressure. Analyses of dHvA oscillations in the mixed state indicate that the influence of the superconducting energy gap is negligible for some orbits.

The magnetic susceptibility and electrical resistivity in the metal-insulator (MI) transition of a mixed-valent Ti-oxide system, Y1-x CaxRTiO3, is investigated as a function of pressure. This system exhibits obviously the temperatureinduced MI transition at x=0. 3-0. 4. At the low temperature metallic phase, susceptibility, X (T), is strongly suppressed with pressure. On the other hand, in the high temperature semiconductiong phase X (T) obeying the Curie-Weiss law is not affected strongly with pressure. The coefficient of the T2-term in resistivity, A, and the residual resistivity, ρ (0), are decreases rapidly with pressure. At x=0. 375 and 0. 39, we recognize the relation of A∝X (10 K) 2 at the low temperature metallic state.

Magnetic properties of CePtAl single crystals with orthorhombic TiNiSn-type crystal structure were investigated for each axis by measurements of magnetic susceptibility, high-field magnetization up to 30 T and magnetoresistance up to 10 T. The pronounced anisotropy observed indicates that magnetism in CePtAl is dominated by a ferromagnetic component along the magnetically easy a-axis and that the magnetically hard axis changes from the c-axis (T > 39 K) to the b-axis (T

The thiospinel ${\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{In}}_{x}{\mathrm{Ir}}_{2}{\mathrm{S}}_{4}(0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.25)$ system was studied by the measurements of crystal structure, electrical resistivity, and magnetic susceptibility. The parent compound was known to exhibit an intriguing first-order metal-insulator (MI) transition with a simultaneous spin-dimerization and charge ordering at $\ensuremath{\sim}230\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ with decreasing temperature. Upon indium doping on the copper site, the conduction holes of the metallic phase are depleted, or the doped electrons occupy the antibonding state of the insulating phase, suppressing the MI transition. Moreover, the first-order transition is changed into a higher-order one for $x\ensuremath{\geqslant}0.2$. Our experimental data suggest that the higher-order phase transition is associated with an electronic transformation from small polarons to small bipolarons. Comparing the doping effects of Zn, Cd, and In, we found that the variations of the electrical and magnetic properties depend on the lattice size, i.e., the suppression of the MI transition becomes weaker for an enlarged lattice. This lattice size effect is mainly explained in terms of the electron-phonon interactions, which is enhanced by the band narrowing due to the larger ionic size of the dopants.

The metal-to-insulator (MI) transition in the Y 1 − x Ca x TiO 3 system is known to occur at x = 0.35. Furthermore, near this critical metallic region, electrical resistivity and magnetic susceptibility show a broad peak around 170 K and are accompanied by clear thermal hysteresis. This thermal hysteresis in magnetic susceptibility is found to vanish at 1.05 GPa. These phenomena can be interpreted as some aspects of a first-order type metal-insulator transition.

The pseudobinary thiospinel system ${\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Cd}}_{x}{\mathrm{Ir}}_{2}{\mathrm{S}}_{4}$ was investigated by the x-ray-diffraction, electrical resistivity, magnetic-susceptibility, and specific-heat measurements. It was shown that the system exhibits a miscibility-gap behavior for the Cd substitution, however, nearly monophasic samples were obtained by quenching at 1373 K, except for $0.4lxl~0.6.$ With increasing the Cd concentration, the room-temperature electrical conductivity and Pauli susceptibility decrease monotonically, consistent with the hole-filling picture. The first-order metal-insulator transition at about 230 K in the parent compound ${\mathrm{CuIr}}_{2}{\mathrm{S}}_{4}$ is changed into a second-order transition around 185 K when $x\ensuremath{\sim}0.25,$ whereafter the second-order transition disappears at $x\ensuremath{\sim}0.8.$ No superconductivity was observed down to 1.8 K. The end-member compound ${\mathrm{CdIr}}_{2}{\mathrm{S}}_{4}$ is shown as an insulator with a band gap of 0.3 eV. Analysis for the data of magnetic susceptibility and electrical resistivity suggests the formation of bipolarons below 185 K for $0.25lxl0.8,$ which accounts for the absence of superconductivity in terms of the transition from the BCS Cooper pairs to small bipolarons.

Measurements of electrical resistivity, magnetic susceptibility and specific heat have been performed on a new ternary compound SmPd2Al3. The results indicate that the valence of Sm ions is almost trivalent and that SmPd2Al3 has a complicated magnetic phase diagram below 12 K.

We have investigated magnetic susceptibility, electrical resistivity and specific heat in polycrystalline and single- crystalline Ce1−xLaxPd2Al3 (x = 0−0.1) reported recently as a new heavy fermion system. The sample dependence observed at low temperatures suggests that this system is situated in the region, TK ≈ TRKKY.

The thiospinel system ${\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Zn}}_{x}{\mathrm{Ir}}_{2}{\mathrm{S}}_{4}$ $(0l~xl~0.9)$ has been studied by x-ray diffraction, electrical resistivity, and magnetic susceptibility measurements. The parent compound ${\mathrm{CuIr}}_{2}{\mathrm{S}}_{4},$ being metallic at room temperature, undergoes a structural phase transition towards lower symmetry around 230 K and becomes an insulator at the low temperature. The Zn substitution for Cu was found to drastically suppress the metal-to-insulator (MI) transition, resulting in the appearance of superconductivity. The MI transition temperature ${T}_{\mathrm{MI}}$ and the extent of the structural distortion both decrease with increasing x until the phase transition is completely suppressed at $x\ensuremath{\sim}0.4.$ In the region of $xl~0.4,$ the cubic spinel phase coexists with the low-symmetry phase below ${T}_{\mathrm{MI}}.$ For the metallic phase, the change of the Pauli paramagnetic susceptibility indicates the hole-filling mechanism due to an excess electron from the Zn substitution for Cu. The insulating state of the low-symmetry phase is tentatively explained in terms of charge ordering combined with the ${\mathrm{Ir}}^{4+}$ dimerization. Bulk type-II superconductivity below 3.4 K is observed for $0.25l~xl~0.8$ samples. The superconducting transition temperature decreases with increasing the Zn content. The abnormal behavior of the normal-state resistivity below 200 K for $0.3l~xl~0.5$ samples suggests modification of the electronic states, which might be related to the occurrence of superconductivity.

A new strontium vanadium sulfide, SrV2S5, has been successfully synthesized, which does not show superconductivity. The powder X-ray diffraction pattern has been indexed from a rhombohedral cell with hexagonal setting lattice constants of a=3.25 and c=35.0 A.The resistivity is low, semiconductive and weakly dependent on temperature above 50 K, and increases rather rapidly below this temperature. The magnetic susceptibility is nearly temperature independent above ~80 K, below 50 K it shows an extremely small Curie like behavior, suggesting singlet pairs of vanadium ions in insulating phase at low temperatures. The magnetic and conducting inherent properties seem to change gradually around 80 K.

In order to characterize the magnetic state at high pressure, anisotropic susceptibilities, χ a , χ b and χ c were measured up to 1.8 GPa in PrCu 2 , which seems to exhibit a pressure-induced Van Vleck paramagent-to-antiferromagnet transition at 1.2 GPa. It is speculated that the ordered 4f-moments lie in the b -plane in the pressure-induced magnetic state. Remarkable pressure-effects on susceptibility are observed in the b -plane, as indicated in the co-operative Jahn-Teller effect and in the metamagnetism under high field.

The thiospinel compound CuIr 2 S 4 exhibits a metal-insulator (MI) transition at about 230 K. It was found that superconductivity appeared after the MI transition being suppressed by Zn substitution for Cu. The superconducting transition temperature decreases from 3.3 K to 2.2 K with increasing of Zn substitution from 25% to 50%. The negative temperature coefficient of resistivity in the normal state suggests some kind of modification of electronic states, which might be related to the occurrence of the superconductivity.

We report on the effect of Zn substitution for Cu in CuIr2S4 spinel, which shows the metal–insulator (MI) transition at about 230 K accompanied with a cubic-to-tetragonal structural phase transformation. It was shown that the solid solution of Cu1−xZnxIr2S4 can be formed for 0⩽x⩽0.5. The MI transition temperature decreases rapidly with increasing Zn content, and no MI transition can be observed for x>0.3. The magnetic susceptibility in metallic state decreases with the Zn substitution, suggesting a hole-filling mechanism. Low-temperature X-ray diffraction revealed that the tetragonal distortion of insulating phase decreased with increasing Zn content.

We measured the electrical resistivity and ac magnetic susceptibility of BaFe2As2 and SrFe2As2 single crystals under pressure using a cubic anvil apparatus. For BaFe2As2, the antiferromagnetic (AF) and structural transitions are suppressed with increasing pressure. Unexpectedly, these transitions persist up to 8 GPa, and no signature of a superconducting transition was observed in the pressure range investigated here. On the other hand, the AF and structural transitions of SrFe2As2 collapse at around the critical pressure Pc ~ 5 GPa, resulting in the appearance of bulk superconductivity. The superconducting volume fraction abruptly increases above Pc, and shows a dome centered at approximately 6 GPa. Our results suggest that the bulk superconducting phase competes with the AF/orthorhombic phase and only appears in the narrow pressure region of the tetragonal phase., 4 pages, 4 figures; accepted for publication in J. Phys. Soc. Jpn

Single-crystalline CeRh 2 Si 2 and CePd 2 Si 2 were grown by the Czochralsky pulling method and the temperature dependence of magnetic susceptibility was investigated. The crystalline electric field (CEF) states in each compound were determined by considering the tetragonal CEF Hamiltonian with mean-field approximation. Interactions between Ce 3+ ion and the surrounding ligands in CeRh 2 Si 2 turned out to be strong and highly anisotropic in comparison to CePd 2 Si 2 .

Crystal structure, electrical resistivity and magnetic susceptibility were studied for a new superconducting complex cuprate, Sr 0.4 Ca 13.6 Cu 24 O 41+σ . The crystal structure consists of S=1/2 Heisenberg two leg ladder and 1-D chain systems, in which atomic positions are modulated along the c direction. The resistivity decreases with increasing pressure, and superconductivity was observed with the maximum T c onset =13K at 5GPa. From the analysis of the magnetic susceptibility data at ambient pressure using an alternating chain model, we found that AF (anti-ferro) dimers in the 1-D chain are linked by weak AF interaction.

We have investigated the magnetic susceptibility at atmospheric pressure for the (Y1−xPrx)2Ba4Cu7O15−δ system with x=0.1−0.6 and that at high pressure for the sample with x=06. The effective moment per Pr ion obtained by the Curie-Weiss fitting is an intermediate value between that expected for Pr3+ and that for Pr4+. It was found that the magnetic state of Pr ion is scarcely affected by pressure.

The magnetic susceptibility in α- and γ-Ce have been studied under high pressure up to 1.2 GPa. The magnetic susceptibility of γ-Ce obeys the Curie-Weiss law and the Weiss temperature is considerably increased with increasing pressure. On the other hand, the susceptibility of α-Ce becomes nearly temperature independent at higher pressure. These behaviour can be semiquantitatively explained by the single impurity Kondo picture resulting in the Kondo or spin-fluctuation temperatures as a function of volume.

The enhancement of the superconducting transition temperature by pressure was studied up to 2 GPa for an YBa2Cu4O8 compound which was synthesized by using the canned HIP technique. The value of dT c/dP was found to be 5.5 K/GPa. From the experiments of the specimen in which YBa2Cu4O8 and Y2Ba4Cu7O14 compounds coexist, dT c/dP for Y2Ba4Cu7O14 was also shown to be 5.5 K/GPa. The result for the YBa2Cu4O8 compound is explained by the pressure induced carrier (hole) redistribution on the basis of the calculation of the Madelung energy.

Transport and magnetic properties of the T'-phase Nd2-x Ce x CuO4 system have been studied to investigate the occurrence of superconductivity by electron doping. The lattice constants and susceptibility of the system are reasonably interpreted in terms of all the Ce ions being tetravalent. The resistivity decreases by more than three orders of magnitude with Ce doping up to x=0.2. The measurements of thermopower confirm that the resistivity decrease arises from the increase of electron carriers supplied by the Ce4+ ions. Anomalous resistivity decreases are observed below 11 K, suggesting the occurrence of superconductivity in this system.