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High-field magnetization and neutron diffraction measurements were performed on the one-dimensional compound Ca 3 CoRhO 6 . The long-range ordered state was first observed below 90 K. A plateau at 1/3 of the saturation magnetization was observed in the magnetization curve at 70 K, indicating ferrimagnetic alignment of the ferromagnetic Ising chains. We also observed a large hysteresis originating from a spin freezing of ferromagnetic chains in the magnetization curve at 4.2 K. Based on the results of high-field magnetization and neutron diffraction measurements, a possible magnetic structure is discussed in terms of the spin frustration on the triangular lattice.

The structure, magnetization and electrical resistance for the La2-xSrxMnRuO6 system with double-perovskite structure were investigated. The structural transition from an orthorhombic cell with a random arrangement of Mn and Ru to a cubic cell (rock salt sublattice) with an ordered arrangement occurs at near x=1.0. All samples La2-xSrx MnRuO6 (0 less than or equal tox less than or equal to2.0) show semiconducting behavior. The conductivity for the samples with x less than or equal to0.3 at higher temperature has a 2-dimensional variable-range-hopping (VRI-I) mechanism. Bur the temperature dependence of resistance for La2-xSxMnRuO6 (1.0 less than or equal tox less than or equal to2.0) samples can be described using neither a VRH mechanism nor a thermal activation mechanism in a single energy gap. The samples with x s less than or equal to2.0) samples show ferromagnetism below 300 K. The molecular field constant radio N-AB/N-AA changes with the doping concentration of Sr for La. (C) 2001 Elsevier Science B.V. All rights reserved.

Temperature and magnetic field variations of the electric resistivitiy ( ρ ) as well as temperature dependence of the magnetic susceptibility ( χ ) are reported for the YbCu 5− x Au x system with the C15b-type structure. These results indicate a systematic composition dependence from dense Kondo to RKKY antiferromagnetic system via quantum critical point with x =0.2–0.4. The logarithmic temperature dependence of ρ was observed in the middle temperature range for all the compositions, implying that the incoherent Kondo scattering is dominant in this T-region. With decreasing temperature, the ρ tends to saturate, makes a maximum, then decreases toward the Fermi liquid ground state due to the coherent dense Kondo effect ( x x >0.4). The non-Fermi liquid behavior was observed around the quantum critical composition ( x =0.2–0.4).

YbCu5 shows a typical heavy-fermion behaviour while YbCu4Au exhibits an antiferromagnetic transition below 1 K. We have investigated the low-temperature electrical resistivity, ρ, of the pseudo-binary compound YbCu5-xAux (0≤x≤1.0) as functions of temperature (T) and magnetic field (H). The ρ(T) data indicate that the magnetic transition occurs for x = 1.0, 0.8, and 0.6 at Torder = 0.6, 0.4, 0.1 K, respectively, whereas magnetic ordering is absent for x≤0.2 down to the lowest temperature. ρ(H) for x = 0, 0.1, and 0.2 measured at 0.05 K shows a characteristic behaviour in the non-magnetic Kondo-lattice state. It has been found that the increase of the Au concentration x results in a rapid decrease of the Kondo temperature, TK, as well as the evolution of impurity Kondo behaviour, destroying the Kondo-lattice state for x = 0. This may imply that the Au substitution causes a significant change of the local electronic structures. ρ(T) for x = 0.6 varies nearly as T3/2 at 0.5 T below 0.15 K, while it shows a T2-power law at 1 T. This behaviour can be interpreted as the crossover caused by a magnetic field from a magnetic ordered state at zero field through a non-Fermi-liquid state to the Fermi-liquid state at high field.

From the resistivity and magnetic susceptibility measurements of polycrystalline Bi x V 8 O 16 with 1.6< x

Physical properties of the heavy-fermion system YbCu5 and the YbCu5−xAgx compounds are studied in high magnetic fields. These systems show metamagnetic-like behavior at low temperature. This can be qualitatively explained by the Bethe-ansatz solution of the Coqblin–Schrieffer model. A large negative magnetostriction is observed in YbCu5 at low temperature, which indicates a valence change of Yb by field: from the valence-fluctuating state with itinerant 4f-electrons at low field to a stable Yb3+ state with localized magnetic moments at high field.

In order to clarify the variation of the microscopic magnetic nature with the carrier density in Na x CoO 2 · y H 2 O , we have measured positive muon-spin rotation/relaxation ( μ + SR ) spectra for H2O as well as D2O absorbed samples. Based on the zero field (ZF-) μ + SR measurements, there was no clear difference between the two superconducting phases (SC-I and SC-II). Furthermore, the ZF-spectrum for the H2O absorbed sample exhibits a clear oscillation in the whole T range measured (1.4–100 K), suggesting the formation of “[H3O]+-like” H2μ+O ions in the sample. Further, the absence of an oscillation in the D2O absorbed sample also evidences the presence of H2μ+O. We also measured 59Co nuclear quadrupole resonance spectra of magnetic sample. The temperature dependence of spectra shows that there is no evidence of charge ordering and CDW ordering around magnetic transition temperature.

The magnetization of V 5 S 8 and V 5 Se 8 was measured in pulsed high magnetic fields up to 39 T. The anomalies were observed in the magnetization curves for both V 5 S 8 and V 5 Se 8 . For V 5 S 8 , the anomaly at lower field is thought to correspond to spin flopping. The magnetization curves exhibited saturation for both compounds and the values of the ordered moments for V 5 S 8 and V 5 Se 8 were estimated to be 1.5 and 1.2 μ B /V I from the saturation moments, respectively. Our results support the magnetic structure of V 5 S 8 proposed by neutron diffraction measurements.

The magnetic and electrical properties are reported in the new solid solutions BaCo 1- x Cu x S 2 and BaNi 1- x Fe x S 2 . Both compounds show spin-glass-like behavior, although the type of spin fr...

Magnetic properties of Sr 1- x Ca x RuO 3 have been investigated at temperatures from 4.2 up to 300 K and in magnetic fields up to 44 Tesla. The results of high-field magnetization process are consistent with the interpretation that this system ranges from an intermediate itinerant ferromagnetic metal to a strongly exchange-enhanced Pauli paramagnet (a nearly ferromagnetic metal) with increase of x . Although all the samples have indicated very large high-field magnetic susceptibility, no symptoms of the occurrence of itinerant-electron metamagnetism, which is seen in some nearly ferromagnetic metals like YCo 2 , have been observed.

The layered compounds Ba 1- x Bi x CoS 2 (0≤ x ≤0.7) were prepared in a single phase of the BaCoS 2 type. The electric resistivity was found to be drastically decreased with x and shows a systematic change from insulating to metallic with decreasing temperatures: the electric resistivity for x ≥0.05 follows the T 2 -dependence below 20 K, indicating that the Fermi liquid state is realized at low temperatures, while it shows semiconducting temperature dependence at high temperatures. The electronic specific heat coefficient γ for Ba 0.95 Bi 0.05 CoS 2 was estimated to be a small value of 3.5 mJ/mol·K 2 instead of the large T 2 -term in the resistivity. In magnetic susceptibility measurements, the antiferromagnetic ordering was found to be stable even in metallic samples. These results can be understood as: two types of electronic bands near the Fermi level in the electron-doped BaCoS 2 , one of which has the Mott-Hubbard gap giving rise to the antiferromagnetic ordering just as BaCoS 2 and the other has a ...

One-dimensional compounds Ca3CoRhO6 and Ca3FeRhO6 have been newly synthesized and structurally characterized by Rietveld refinement of powder X-ray diffraction data. Both compounds are isostructural with the rhombohedral K4CdCl6-type structure (space group R 3 c; Z=6; Ca3CoRhO6: a=9.2017(1) A, c=10.7296(1) A Ca3FeRhO6: a=9.1960(1) A, c=10.7861(1) A). The structure of Ca3CoRhO6 and Ca3FeRhO6 contains one-dimensional chains consisting of alternating faced-sharing CoO6, FeO6 trigonal prisms, and RhO6 octahedra, respectively. The magnetic susceptibility of Ca3CoRhO6 exhibits an abrupt drop at 35 K, which is also observed in Sr3NiIrO6 and Ca3CoIrO6. Ca3FeRhO6 is an antiferromagnet with TN=12 K.

The stability of normal mode oscillations has been studied in detail under the single-mode excitation condition for the Fermi-Pasta-Ulam-$\ensuremath{\beta}$ lattice. Numerical experiments indicate that the mode stability depends strongly on $k/N,$ where k is the wave number of the initially excited mode and N is the number of degrees of freedom in the system. It has been found that this feature does not change when N increases. We propose an average variational equation --- approximate version of the variational equation --- as a theoretical tool to facilitate a linear stability analysis. It is shown that this strong $k/N$ dependence of the mode stability can be explained from the view point of the linear stability of the relevant orbits. We introduce a low-dimensional approximation of the average variational equation, which approximately describes the time evolution of variations in four normal mode amplitudes. The linear stability analysis based on this four-mode approximation demonstrates that the parametric instability mechanism plays a crucial role in the strong $k/N$ dependence of the mode stability.

We have investigated the physical properties of Pb 2 - x Ln x Ru 2 O 7 - δ ( Ln = Sm , Eu ) compounds with pyrochlore crystal structure. The solid-solution compounds of Pb 2 - x Ln x Ru 2 O 7 - δ show from metallic ( x = 0 ) to insulating ( x = 2 ) behaviors. These compounds with x > 1.0 also indicate the spin-glass like behaviors at low temperature ( T T SG ) which are attributed to the geometrical frustration on pyrochlore lattice. The transition temperature T SG decreases monotonously with decreasing x and goes to zero at x = 0.6 . The sample with 0.4 ⩽ x ⩽ 0.8 shows the metal–insulator (MI) transition at 10–30 K where the sign of temperature derivative of electric resistivity changes.

Two novel three-dimensional (3D) 3d-4f mixed complexes [Ln(H(2)O)(4)][Ni(2)TTHA(SCN)(2)].H(3)O+ [Ln = Pr (1), Ce (2); H(6)TTHA = triethylenetetraaminehexaacetic acid], based on the building blocks of [Ni(2)TTHA(SCN)(2)](4-), were synthesized and characterized by X-ray crystal diffraction and magnetic properties. The single-crystal structures show that these complexes form a 3D framework, comprised of an unusual infinite one-dimensional chain based on heterometallic Ln2Ni2 rings. The temperature-dependent magnetic susceptibilities were analyzed by an approximate model, leading to g = 2.06. Delta = 2.83, zJ' = -0.6 cm-1 for complex 1 and g = 2.07, Delta = 1.00, zJ' = -0.5 cm(-1) for complex 2.

We have studied electronic structures of VO 2 by soft and hard X-ray synchrotron core-level photoelectron spectroscopy. In our measurements, temperature and photon energy dependences of the V 2p core-level spectra are observed. Remarkable spectral changes are observed across the metal-insulator transition (MIT) at T = 340 K . A clear shoulder structure is observed on the lower binding energy side of the V 2 p 3 / 2 peak in the metallic phase. This shoulder structure, being stronger for larger h ν , is interpreted as the well-screened feature by bulk conduction electrons.

We studied magnetic excitations of a spin-gapped compound Na 2 Cu 2 TeO 6 , the hole doping effect on the Cu 2 TeO 6 plane via topotactic Na deficiency introduced by soft-chemical treatment, the spin vacancy effect by Zn substitution and the magnetic impurity effect by Ni substitution for Cu by means of magnetic susceptibility measurements. It turned out that unpaired moments of the doped holes by Na deficiency, Zn and Ni impurities induce Curie magnetism and lower the broad maximum temperature T max in the uniform spin susceptibility. The decrease of T max indicates the decrease of a predominant superexchange interaction.

Pb 2 V 3 O 9 is an S = 1 2 alternating spin chain compound with a spin-gap. We have observed field- and impurity- induced antiferromagnetic long range order (AF-LRO) in this system. We made phase diagrams for each case from the temperature dependence of magnetic susceptibility χ measurement. For both perturbation induced AF-LRO, the increase of T N was commonly observed in the low magnetic field and the low impurity concentration regions. However, the behavior of χ below T N for each case is quite different; one increases and the other decreases. These contrastive behaviors originate from spatially different characters of the induced moments by the perturbations introduced to the spin-gap system.

We have studied the synthesis and physical properties of misfit cobaltates compounds intercalated by the iodine. The iodine atoms was successfully intercalated into the misfit cobaltates by the heat treatment at a constant iodine partial pressure. In the case of Bi(Pb)–Sr–Co–O system, I α Bi 2 - x Pb x Sr 2 Co 2 O y , it was found that the c -axis drastically increased by the intercalation. The iodine content α was determined to be 0.97 for Pb content x = 0 , and 0.81–0.85 for x > 0.4 . From magnetic and electric measurements for these compounds, it was suggested that the intra-layer couplings between CoO 2 layers are probably reduced by the iodine intercalation.

High resolution synchrotron X-ray diffraction methods have been used to study the crystal structure of the two-dimensional square-lattice antiferromagnets ( CuCl ) LaNb 2 O 7 and ( FeCl ) LaNb 2 O 7 . While the structure of the former is of tetragonal symmetry with simple perovskite unit cell dimensions in the a , b plane ( a × a ) , the latter exhibits a tiny orthorhombic distortion with a 2 a × 2 a × c superstructure, providing a first example of modulation in the family of transition-metal oxyhalides prepared from topotactic ion-exchange reactions. Possible arrangement in the FeCl layer is proposed.

High field ESR measurements have been performed on newly synthesized layered manganese oxides A 4 Mn 3 O 10 (A=Ba, Sr) using a pulsed magnetic field up to 16 T. From the temperature and the frequency dependence measurements, it was confirmed that both ground states at low temperature are the antiferromagnetic ordered state. The typical AFMR absorption lines were observed for both compounds and both were well explained by the AFMR theory for a two-sublattice antiferromagnet with orthorhombic magnetic anisotropy. Moreover, we found that the magnetic anisotropy energies in these compounds are very small as compared with their exchange interactions.

New one-dimensional compounds Ca3CoBO6(B=Ir, Ru) with K4CdCl6-type structure have been synthesized by conventional solid state reactions. Both compounds adopt the rhombohedral symmetry with the space groupR 3 c;a=9.1811(1) A,c=10.8232(3) A,Z=6 (hexagonal expression) for Ca3CoIrO6anda=9.1921(3) A,c=10.7784(7) A,Z=6 for Ca3CoRuO6. One-dimensional chains are built by alternating face-shared CoO6octahedra andBO6trigonal prisms. The magnetic susceptibility of Ca3CoIrO6shows an abrupt drop at 30 K, as seen in the case of Sr3NilrO6, suggesting that ferromagnetic chains couple antiferromagnetically. On the contrary, Ca3CoRuO6is an ordinary antiferromagnet withTN=55 K. We have also succeeded in preparing the solid solution series, Ca3Co1+xIr1−xO6and Ca3Co1+xRu1−xO6(0≤x≤1), and magnetic properties of these systems were investigated.

Y2Ba4Cu7O15−δcompounds were characterized by microscopic investigation using TEM and NQR techniques. We synthesized Y247 compounds by two kinds of preparation methods: the conventional solid-state reaction (sample A) and the polymerized-complex method (sample B). The value ofTcfor sample A was found to be 65 K and that for sample B was 93 K by ac-χmeasurements. As a result of TEM experiments, stacking faults along thecaxis were observed more frequently in sample B than in sample A. These stacking faults resulted in microdomains containing pure Y123 or Y124 thin blocks of several unit cells. NQR experiments revealed that the microscopic environment of Cu(2) sites in sample A differed from either of those in the Y123 and Y124 compounds. NQR frequency values (νQ) of Cu(2) sites agreed well with those calculated by the point charge model applied for the Y247 structure. The spectra of Cu(2) sites in sample B could be regarded, however, as a combination of those of pure Y123, Y124, and also Y247 compounds. This fact was coincident with the result of TEM experiments. We concluded that the superconductivity of Y247 with higherTcoriginates from the thin block of Y123.

Anisotropies of the spin-lattice relaxation rates (1/ T 1 ) at the Cu(1) sites of YBa 2 Cu 3 O 7 and YBa 2 Cu 4 O 8 were examined using the NMR/NQR methods. The anisotropy data enabled us to infer approximate q-dependences and anisotropies of the form factors ( F α ( q y ), α= a , b , c ) at Cu(1). We found that the anisotropies in YBa 2 Cu 3 O 7 are explainable only in terms of the hyperfine fields within a single chain, while these hyperfine fields do not account for anisotropies in YBa 2 Cu 4 O 8 . As a possible explanation for the situation in YBa 2 Cu 4 O 8 , effects of the transferred hyperfine fields from the other chain of the double Cu-O chains are discussed.

Cubic AuBe 5 -type YbCu 5− x Al x (0≤ x ≤0.5) has been prepared for the first time under a pressure of 1.5 GPa and at 650°C. Magnetic susceptibility measurements indicate that cubic YbCu 5− x Al x exhibits Curie–Weiss behavior down to 4 K, except for YbCu 5 that displays a maximum at 10 K due to Fermi liquid formation. The Yb ion in this system is found to be in a stable trivalent state (4f 13 , J =7/2) with a localized moment close to 4.54 μ B of free Yb 3+ ion. Contrary to the consistent magnetic behavior, the temperature dependence of electrical resistivities of YbCu 5− x Al x displays a systematic transition from a typical Fermi liquid behaviour ρ ( T )∝ T 2 ( x ≤0.1) to a Kondo impurity behavior ρ ( T )∝−log T ( x ≥0.3). The characteristic Kondo temperature T K is largely lowered during this crossover.

Magnetic properties of Ca 3 Co 2 O 6 with ferromagnetic Ising chains have been studied using oriented sample along the chain direction. From the extremely anisotropic behavior in its magnetization at low temperatures and in the temperature dependence of magnetic susceptibility, it is suggested that an octahedral Co 3+ is nonmagnetic, whereas a trigonal prismatic Co 3+ has a fictitious spin S '=1 with large single-ion anisotropy ( D ∼-25 K, g // ∼4). At low temperatures below 5 K, multisteps are observed in the magnetization, suggesting the existence of various magnetic structures. The pulsed magnetization measurements reveal that the response of ferromagnetic chains to the field is slow and varies as a function of temperature and Δ H /Δ t .

We have succeeded in synthesizing the insulating phase of Bi 2 Sr 2 CuO 6+δ (Bi2201) with the stoichiometric cation composition by use of a heat treatment technique in an evacuated tube with titanium powders. The excess oxygen content δ and the average valence of Bi were determined electrochemically by the coulometric titration method. The value of δ in the insulating phase was found to be 0.02. The hole concentration h was also estimated with values of δ and the average valence of Bi in Bi2201. As a result, temperature dependence of resistivity and h dependence of Tc and Meissner volume fraction indicated behaviors similar to those of other high-Tc systems. The antiferromagnetic order of Cu 2+ spins in the insulating Bi2201 phase has been confirmed by nuclear magnetic resonance. Thus, we can obtain the three distinct electronic states observed in high-Tc oxides, i.e., over-doped metallic, superconducting, and antiferromagnetic phases in Bi2201 compounds by changing only the oxygen content. The static parameters of the hyperfine field and the electric field gradient at Cu sites in Bi 2 Sr 2 CuO 0.62 were found to be almost comparable to those of other antiferromagnetic phases of high-Tc oxides.

We have measured the M\"ossbauer effect of ${}^{57}{\mathrm{Fe}}^{3+}(S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}5/2)$ ions doped in a 1D Ising ferromagnet C${\mathrm{a}}_{3}$C${\mathrm{o}}_{2}$${\mathrm{O}}_{6}$. The spectra with hyperfine fields corresponding to the exchange polarized Fe electron spins with ${m}_{z}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ifmmode\pm\else\textpm\fi{}5/2,\ifmmode\pm\else\textpm\fi{}3/2,\ifmmode\pm\else\textpm\fi{}1/2$ are first observed in the magnetically dense system for $T\ensuremath{\le}20\mathrm{K}$, suggesting slow magnetic relaxation at the ${\mathrm{Fe}}^{3+}$ sites. The key lies in the large difference between magnetic characters of the host (Ising) and impurity (Heisenberg) spins, making the impurity spins extremely isolated in the host 1D Ising spin system.

The ${\mathrm{YbCu}}_{5}$ phase with $C15b$ structure has been prepared by a high-pressure technique, and its physical properties have been investigated. The temperature dependence of magnetic susceptibility, electrical resistivity, and specific heat show Kondo-lattice formation. Furthermore, a heavy Fermi-liquid state without magnetic ordering down to 2.0 K is found to evolve below about 6 K. The electronic specific heat coefficient \ensuremath{\gamma} is enhanced to values as large as to 550 mJ/mol ${\mathrm{K}}^{2}$. The magnetization measured up to 40 T at 1.6 K has a field dependence which is expected for a Kondo system when the total angular momentum is $Jg1.$ All results are in good agreement with the extrapolation of the previous results of ${\mathrm{YbCu}}_{5\ensuremath{-}x}{\mathrm{Ag}}_{x} (0.125l~xl~1.0)$ for $x\ensuremath{\rightarrow}0$. The concentration dependence of characteristic temperatures of ${\mathrm{YbCu}}_{5\ensuremath{-}x}{\mathrm{Ag}}_{x}$ can be quantitatively explained by the chemical pressure effect within the compressible Kondo model for the full range of Ag concentration ( $0.0l~xl~1.0).$ The origins of Kondo-lattice formation in ${\mathrm{YbCu}}_{4}$Ag and the valence transition in ${\mathrm{YbCu}}_{4}$In are discussed.

Magnetization measurements on the one-dimensional oxide Ca 3 Co 2 O 6 having a triangular net of Co 2 O 6 chains have been carried out both in static and pulsed high magnetic fields. The M / H vs. T curve obeys the Curie-Weiss law at high temperatures. Below 25 K, however, M / H increases abruptly, and a plateau is observed at 1/3 of the full moment in the M - H curve, suggesting a ferrimagnetic state of the ferromagnetic chains due to the antiferromagnetic interchain interaction. At low H , this system is considered to be in a partially disordered antiferromagnetic state for 10 K< T

We found the field-induced magnetic ordering for a quasi-one-dimensional alternating spin chain compound Pb2V3O9, which can be understood by Bose–Einstein condensation of triplons. In this paper, we present the temperature-field magnetic phase diagram, which is drawn from magnetic susceptibility, high field magnetization and 51V NMR measurements.

V6O13 and VO2 show metal–insulator transition at about 145 and 340 K, respectively. They are metallic above the transition temperature ( T t ) and insulating below T t . We have performed the angle resolved photoemission measurements (ARPES) with the resolution of 160 meV above and below T t by resonantly exciting the V 3d component in addition to the angle intergrated photoemission spectroscopy. The raw energy distribution curves of ARPES of V6O13 show different behaviors between metallic and insulating phases. In the metallic phase, there is a dispersion just below the Fermi level, but no noticeable dispersion is observed in the insulating phase. In the metallic phase of VO2, the coherent peak was prominently observed compared with the incoherent part in contrast to the spectra taken at low photon energies.

We performed 59Co NMR and NQR measurements of Na 0.35 CoO 2 · 1.3 H 2 O superconductor with T c of about 5 K in order to decide the pairing symmetry of the Cooper pairs. From NQR measurements, it was found that the increase in 1 / T 1 T above T c is attributed to nearly ferromagnetic fluctuations. The spin contributed Knight shift was estimated by δ ν / ( γ N H i ) vs. ( γ N H i ) - 2 plot. Consequently, the Knight shift below T c is invariant at 7 T. This result suggests the possibility of unconventional superconductivity with the spin-triplet state of p- or f-wave pairing symmetry.

We studied the 2D NMR spectrum on the novel superconductor Na 0.35 CoO 2 · 1.3 H 2 O . The temperature dependence of Knight shift at 2D in the normal state is parallel to that of magnetic susceptibility and the hyperfine coupling constant is estimated as 0.16 kOe / μ B . The resonance frequency in the low temperatures does not change below T c , which is contrast to that in 59Co site.

Since the Bose-Einstein condensation (BEC) phenomenon was observed in the field-induced antiferromagnetic state of TlCuCl 3 , the BEC has attracted much interest from the aspect of quantum phase transition in the spin system. Very recently, we measured magnetic susceptibility and high field magnetization for ID spin chain system, Pb 2 V 3 O 9 , and found that the ground state of Pb 2 V 3 O 9 is of gapped spin singlet, which can be destroyed by the magnetic field above 5.2 T. This compound is thought to be a candidate for exhibiting BEC. As a result of magnetic measurements under high magnetic field, we have found a magnetic transition similar to the case of TlCuCl 3 , when we applied magnetic field above 5.6T to this compound.

Bi x V 8 O 16 shows a temperature-induced metal–insulator transition (MIT) in the Bi composition range of 1.72 ⩽ x ⩽ 1.80 . The magnetic susceptibility χ of the compound with 1.72 ⩽ x ⩽ 1.80 shows an anomaly at the MIT temperature T MIT . Below T MIT , χ shows a rapid increase with decreasing temperature, following a Curie–Weiss law. The effective moment estimated from susceptibility below T MIT is about 0.4 μ B /(V atom). In order to reveal the origin of the magnetic moment below T MIT , we performed a V 51 -NMR study. Observation of the V 51 -NMR signal below T MIT indicates the existence of non-magnetic vanadium sites. The marked decrease of the absolute value of the Knight shift at low temperatures suggests the spin-singlet nature of the ground state. The origin of the small magnetic moment is attributed to the formation of the spin-singlet state.

We have measured magnetization under high pressure of Yb0.9Y0.1InCu4 which exhibits a valence transition at T v = 28 K . With applying pressure, T v is lowered. At P = 1.6 GPa , collapse of the valence transition and the occurrence of ferromagnetism are simultaneously observed. Considering the results of Yb0.8Y0.2InCu4, both of the phenomena are definitely related. The Curie temperature of this ferromagnetism is estimated to be 2.3 K.

The magnetic properties of ThCr${}_{2}$Si${}_{2}$-type single crystals $A$Co${}_{2}$Se${}_{2}$ ($A=\text{K}$, Rb, and Cs) were investigated by means of magnetic susceptibilities and isothermal magnetizations measurements. The ferromagnetic phase transition temperatures are $\ensuremath{\approx}$74 and 76 K for $A=\text{K}$ and Rb, respectively. A possible antiferromagnetic phase transition occurs around 80 K in susceptibility and a metamagnetismlike behavior is first discovered at a field of $\ensuremath{\approx}$3.5 T for $H\ensuremath{\parallel}ab$ plane in CsCo${}_{2}$Se${}_{2}$ below 62 K. The susceptibilities in the paramagnetic state obey the modified Curie-Weiss law quite well in all samples. Moreover, the derived effective magnetic moments of the Co atom are about 2.21, 2.04, and 2.04 ${\ensuremath{\mu}}_{B}$/Co for $A=\text{K}$, Rb, and Cs, respectively. The generalized Rhodes-Wohlfarth ratio indicates an itinerant magnetism in this series. Finally, we discussed the magnetic properties in this series within the frameworks of the self-consistent renormalization and Takahashi's theory of spin fluctuations.

We report results of NMR experiments on a single crystal of the quasi one-dimensional frustrated magnet LiCuVO_4. The NMR spectra of ^7Li and ^{51}V nuclei indicate a helical spin order in a magnetic field of 4 T with the helical spin plane perpendicular to the field and a spin-density-wave (SDW) order at 10 T with modulation in the magnitude of the moments aligned along the field, in agreement with earlier reports. The nuclear spin-lattice relaxation rate 1/T_1 at ^{51}V nuclei, which is selectively coupled to the transverse spin fluctuations perpendicular to the field, shows a pronounced peak near the helical ordering temperature in the field of 4 T applied along the a-axis. In the field of 10 T, however, such a peak is absent. Instead 1/T_1 at ^7Li nuclei probing longitudinal spin fluctuations shows divergent behavior towards the SDW ordering temperature. These results are qualitatively consistent with the theoretical description that the SDW correlation is due to bound magnon pairs, which produce an energy gap in the transverse spin excitation spectrum., Comment: 14 pages, 7 figures, 3 tables, accepted for publication in J. Phys. Soc. Jpn

Scaling relationships for Nmr spin-lattice relaxation time T 1 and Gaussian transverse relaxation tme T 2G c reviewed and applied to analyse experiments in the normal state of YBa2Cu4O8. Studies of T 2G in the superconducting state are analysed using the theory of Pines and Wrobel to show a preference for d-state orbital pairing over anisotropic s-state. Data on 13C Nmr in the normal and superconducting state of the two dimensional organic conductor (ET)2Cu[N(CN)2]Br are presented and shown to have great similarity to that of the cuprates.

The cubic YbCu 5 compound with the AuBe 5 -type structure was prepared for the first time under a pressure of 1.5 GPa and annealed at 650°C. The previously reported hexagonal YbCu 5 phase with the CaCu 5 -type structure was also confirmed to be stable under relatively lower pressure and at higher temperature. In contrast to the divalent non-magnetic state of Yb ion in the hexagonal phase. Yb ion in the cubic phase was found to be in the trivalent magnetic state. The cubic YbCu 5 phase probably presents a reasonable conjunction for a family of isostructural YbCu 5 , M 1 (M = In, Ag, etc.) compounds, both in crystallographic aspect and in physical properties.

We report here the results of Debye-Scherrer X-ray diffraction measurements in the temperature range from 12K to 300K of the perovskite compounds SrRuO3 and CaRuO3. We show that SrRuO3 indicates an clear anomaly with the temperature dependence of the unit-cell parameters and volume below its ferromagnetic transition temperature Tc of 160K through magnetovolume effect. In particular, the volume of SrRuO3 is almost constant below Tc, and invar effect is discovered for the first time in transition-metal oxide, which is seen in 3d transition-metal itinerant magnets, e.g., Fe-Ni alloy. Therefore, it is concluded that SrRuO3 is classified to a moderately weak itinerant ferromagnet. On the other hand, CaRuO3 shows no anomaly in the variation of the volume with temperature, suggesting that magnetic ordering does not occur in this compound.

The interlayer coupling of superconducting NbN thin films through metallic Ag and insulating CNx thin films has been investigated from resistivity measurements of [ NbN (170 A )/ X (t A )] 10 (X  Ag, CNx) multilayered films. When Ag layer thicknesses are thicker than 150 Am NbN layers are decoupled and the transition temperatures are nearly equal 8.2 K. The transition transition temperature increases with decreasing Ag layer thickness, obeying Werthamer's theory for the proximity effect. On the other hand, with the increase of CNx layer thickness, the transition temperature is lowered steeply and almost linearly, indicating a coupling mechanism other than the proximity effect.

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We show that the quasi-skutterudite superconductor ${\mathrm{Sr}}_{3}{\mathrm{Ir}}_{4}{\mathrm{Sn}}_{13}$ undergoes a structural transition from a simple cubic parent structure, the $I$ phase, to a superlattice variant, the ${I}^{\ensuremath{'}}$ phase, which has a lattice parameter twice that of the high temperature phase. We argue that the superlattice distortion is associated with a charge density wave transition of the conduction electron system and demonstrate that the superlattice transition temperature ${T}^{*}$ can be suppressed to zero by combining chemical and physical pressure. This enables the first comprehensive investigation of a superlattice quantum phase transition and its interplay with superconductivity in a cubic charge density wave system.