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The Curie temperature TC of the weakly ferromagnetic system FeGa3−yGey is investigated by means of isothermal magnetization experiments. The critical temperature of the ferromagnetic phase transition is estimated by the so-called M4 plots rather than the Arrott plots technique. The M4 plots are exploited from the sixth power term of the expanded free energy, which is neglected by the Arrott plots. The magnetic properties are analyzed by taking into account the effects of spin fluctuations in terms of related spin-fluctuation theories.

Single crystals of Fe1-xCoxTe0.85 have been synthesized successfully with x = 0, 0.02, 0.03, 0.05 and 0.10. The cobalt can be substituted for the iron site as Fe1-xCoxTe0.85 up to a solubility limit of x = 0.10, above which an impurity phase was observed. We obtained the intrinsic susceptibilities of these samples by Honda-Owen plot. The antiferromagnetic transition temperature decreases from about 70 K (x = 0) to 34 K (x = 0.05) with increasing the Co substitution level. Superconductivity was not discovered in this series, but a spin-glass like behavior was observed in 5 % substituted sample.

Fe3GeTe2 was synthesized by solid state reaction and chemical transport methods. Our magnetic measurements show that it is a ferromagnet with the Curie temperature of 226 K. The Rhodes-Wohlfarth ratio Pc/Ps∼6.6 indicates that it is an itinerant ferromagnet. On the other hand, we found the single crystal sample with the Curie temperature of 146 K shows the large anisotropy in the temperature dependence of magnetic susceptibilities and the magnetization curves when the external magnetic fields are applied along the c axis and within the ab plane.

We successfully synthesized itinerant-electron ferromagnetic compound LaCoAsO and studied its magnetic properties based on the self-consistent renormalization theory of spin fluctuations and Takahashi's spin-fluctuation theory. We showed that the magnetization (M) of LaCoAsO shows the convex behavior when plotted in the form of M 2 vs H/M, while the M 4 shows the almost linear relation against H/M, which is predicted in the Takahashi's theory. From the comparison between the experimentally observed magnetic susceptibility and calculated one by using the self-consistent renormalization theory, we showed that the nature of spin fluctuations is 3-dimensional around the Curie temperature TC, while above 3TC the difference between two susceptibilities becomes more prominent with increasing temperature, indicating that 2-dimensional spin fluctuations dominate over the 3-dimensional ones in the high temperature region.

We succeeded in synthesizing the bi layer hydrated superconducting Na x CoO 2 · y H 2 O powder samples with different T c 's by systematically changing the duration in a high humidity atmosphere after intercalation of water molecules. From the results of 59Co nuclear quadrupole resonance measurements, it was found that resonance frequency ν Q monotonically decreased with increasing the duration after filtration. The electronic states of samples were found being well characterized by the ν Q , and we succeeded in drawing the electronic phase diagram in which there exist two superconducting phases and an in-between magnetic phase. On the other hand, a lattice parameter along c-axis was found to decrease monotonically with increasing the time duration. This result indicates that shrinkage of CoO 2 planes is caused by changes of arrangements and/or contents of ions between CoO 2 planes which evolve during kept in a high humidity atmosphere.

Ni3AlCx was synthesized by two methods, argon arc melting and solid state reaction methods. X-ray diffraction measurements revealed that the samples prepared by the arc-melting method are in a single phase with the Cu3Au type crystal structure. In x >0.02, all the samples do not show the ferromagnetism but show Pauli paramagnetism while the samples prepared by the solid state reaction method show a tendency of ferromagnetism at about 280 K in the temperature derivative magnetization. From the 27Al NMR measurements, we found the absence of the magnetic phase transition for the samples with x =0.1 prepared by both methods. We conclude that for the samples prepared by the solid state reaction, the enhancement of the magnetization with a tendency of the ferromagnetism is extrinsic, which may be attributed to the possible deposition of Ni-based alloy.

The nuclear quadrupole resonance (NQR) frequency of Co nuclei and the nuclear spin–lattice relaxation rate 1 / T 1 were measured on several bilayered hydrate (BLH) Na x ( H 3 O ) z CoO 2 · y H 2 O ( y ∼ 1.3 ) with variety of superconducting (SC) and magnetic transition temperatures, T c and T M , together with non-SC mono-layered hydrate (MLH) Na x ( H 3 O ) z CoO 2 · y H 2 O ( y ∼ 0.7 ). In the high temperature region above 70 K, 1 / T 1 T in all the samples follows the same temperature dependence which is interpreted as the pseudogap behavior. In the BLH compounds, 1 / T 1 T increases with decreasing temperature below 70 K, and the values of 1 / T 1 T at T c are large in high- T c samples. The magnetic ordering is ascertained from the observation of the prominent divergence of 1 / T 1 T at T M in the samples whose NQR frequency is higher than 12.5 MHz. The temperature dependence of 1 / T 1 T is found to be consistently expressed by a unique function with two fitting parameters. We analyze the temperature dependence of 1 / T 1 T on the basis of this function, and investigate the relationship between the magnetic fluctuations and superconductivity in the BLH compounds.

We report site-selective 63 Cu NMR studies of the vortex core states of an overdoped Tl 2 Ba 2 CuO 6 + δ with T c = 85 K . We observed a relatively high density of low-energy quasi-particle excitations at the vortex cores in a magnetic field of 7.4847 T along the c -axis, in contrast to YBa 2 Cu 3 O 7 - δ .

We found two components of the in-plane Co 59 NMR Knight shift K and different nuclear spin–lattice relaxation rates 1 / T 1 in bilayer hydrated superconductor Na x CoO 2 · y H 2 O , an oriented powder sample by a magnetic field in Fluorinert FC70. Distinguishable two peaks in the central transition line of the Co 59 NMR spectrum at 10 K can be explained by an anisotropic Knight shift in a triangular plane. The hyperfine coupling constants seem to change around 150 K, in which the bulk susceptibility χ shows a broad minimum, suggesting a change of the electronic state in the CoO 2 plane.

Nuclear quadrupole frequency ( ν Q ) and spin-lattice relaxation rate 1/ T 1 of Co were measured on various bilayered hydrate (BLH) Na x CoO 2 · y H 2 O ( y ∼ 1.3) with different values of superconducting (SC) and magnetic-transition temperatures, T c and T M , together with non-SC monolayered hydrate (MLH) Na x CoO 2 · y H 2 O ( y ∼ 0.7). In the temperature range above 70 K, 1/ T 1 T in all samples follows the similar temperature dependence as each other. In the BLH compounds, 1/ T 1 T is enhanced with decreasing temperature below 70 K, and the values of 1/ T 1 T at T c are larger in the higher- ν 3 sample, where ν 3 is the peak frequency of the NQR spectrum arising from ±5/2 ↔ ±7/2 transitions. The magnetic ordering is indicated from the prominent divergence of 1/ T 1 T at T M and the presence of the internal field at the Co nuclear site in the samples with ν 3 higher than 12.5 MHz. We analyze the temperature dependence of 1/ T 1 T in all samples on the basis of identical formula, and discuss the relationship between magnetic fluctuations and superconductivity in the BLH cobaltate.

The family of the superconducting quasiskutterudites (Ca(x)Sr(1-x))(3)Rh(4)Sn(13) features a structural quantum critical point at x(c)=0.9, around which a dome-shaped variation of the superconducting transition temperature T(c) is found. Using specific heat, we probe the normal and the superconducting states of the entire series straddling the quantum critical point. Our analysis indicates a significant lowering of the effective Debye temperature on approaching x(c), which we interpret as a result of phonon softening accompanying the structural instability. Furthermore, a remarkably large enhancement of 2Δ/k(B)T(c) and ΔC/γT(c) beyond the Bardeen-Cooper-Schrieffer values is found in the vicinity of the structural quantum critical point. The phase diagram of (Ca(x)Sr(1-x))(3)Rh(4)Sn(13) thus provides a model system to study the interplay between structural quantum criticality and strong electron-phonon coupling superconductivity.

We synthesized the novel $S=1/2{\mathrm{Mo}}_{3}$ cluster magnet ${\mathrm{Li}}_{2}{\mathrm{ScMo}}_{3}{\mathrm{O}}_{8}$ as well as the isomorphic compound ${\mathrm{Li}}_{2}{\mathrm{InMo}}_{3}{\mathrm{O}}_{8}$, and investigated their macroscopic and microscopic physical properties. ${\mathrm{Li}}_{2}{\mathrm{InMo}}_{3}{\mathrm{O}}_{8}$ showed magnetic ordering at ${T}_{N}\ensuremath{\sim}12$ K with a ${120}^{\ensuremath{\circ}}$ structure, while no magnetic ordering is observed down to 0.5 K in ${\mathrm{Li}}_{2}{\mathrm{ScMo}}_{3}{\mathrm{O}}_{8}$ despite the strong antiferromagnetic interaction among clusters probed by the Weiss temperature. Results of the $^{7}\mathrm{Li}$ nuclear magnetic resonance spectra and the nuclear spin-lattice relaxation rate $(1/{T}_{1})$ measurement show direct microscopic proof of the spin-disordered ground state. We discuss the difference in the ground state between ${\mathrm{Li}}_{2}{\mathrm{ScMo}}_{3}{\mathrm{O}}_{8}$ and ${\mathrm{Li}}_{2}{\mathrm{InMo}}_{3}{\mathrm{O}}_{8}$ using the description of localized magnetism based on spin frustration within the triangular lattice and that of inter- and intracluster charge fluctuations.

We synthesized single crystals of an itinerant ferromagnet ${\mathrm{LaCo}}_{2}{\mathrm{P}}_{2}$ with ${\mathrm{ThCr}}_{2}{\mathrm{Si}}_{2}$-type structure and studied their magnetism by magnetization and ${}^{31}\mathrm{P}$ NMR measurements. We measured Knight shift $K$ and spin-lattice relaxation rate divided by temperature $1/{T}_{1}T$ with the applied fields parallel to the $a$ and $c$ axes, and estimated spin fluctuations in the $ab$ plane and $c$. In addition, we evaluated spin fluctuations from the result of magnetization data with a three-dimensional ferromagnetic model. There is little anisotropy in evaluated spin fluctuations in the $ab$ plane and $c$. Spin fluctuations of ${\mathrm{LaCo}}_{2}{\mathrm{P}}_{2}$ have a three-dimensional character and can be understood in the framework of the self-consistent renormalization theory of spin fluctuations.

The family of the superconducting quasiskutterudites (Ca(x)Sr(1-x))(3)Rh(4)Sn(13) features a structural quantum critical point at x(c)=0.9, around which a dome-shaped variation of the superconducting transition temperature T(c) is found. Using specific heat, we probe the normal and the superconducting states of the entire series straddling the quantum critical point. Our analysis indicates a significant lowering of the effective Debye temperature on approaching x(c), which we interpret as a result of phonon softening accompanying the structural instability. Furthermore, a remarkably large enhancement of 2Δ/k(B)T(c) and ΔC/γT(c) beyond the Bardeen-Cooper-Schrieffer values is found in the vicinity of the structural quantum critical point. The phase diagram of (Ca(x)Sr(1-x))(3)Rh(4)Sn(13) thus provides a model system to study the interplay between structural quantum criticality and strong electron-phonon coupling superconductivity.

We report a $^{205}$Tl NMR study of vortex state for an aligned polycrystalline sample of an overdoped high-$T_c$ superconductor Tl$_2$Ba$_2$CuO$_{6+\delta}$ ($T_{c}\sim$85 K) with magnetic field 2 T along the c axis. We observed an imperfect vortex lattice, so-called Bragg glass at $T$=5 K, coexistence of vortex solid with liquid between 10 and 60 K, and vortex melting between 65 and 85 K. No evidence for local antiferromagnetic ordering at vortex cores was found for our sample.

The physical properties of the rare-earth metal diselenides RS e2− x and rubidium intercalated gadolinium triselenide Rb x GdSe 3− y were investigated. The resistivity and the electron diffraction scattering measurements of RS e2− x revealed that the energy gaps of these semiconductive compounds are related to the presence of the superstructures due to distortion of the Se-layer. All magnetic RS e2 and Rb x GdSe 3− y show antiferromagnetic transition. The anisotropy of the magnetic moment in RSe 2− x and Rb x GdSe 3− y originates in the single ion anisotropy of the rare-earth metal while the direction of magnetic moment in the ordered state originates also in the single ion anisotropy in the case of RS e2− x but in the dipolar interaction in Rb x GdSe 3− y .

A selenate analogue of sodium Jarosite NaFe 3 (SeO 4 ) 2 (OH) 6 has been synthesized by precipitation from aqueous solution. We have newly determined the structural parameters by powder X-ray diffraction refinement. The structure is similar to that of sulfate Jarosite analogues, while the unit cell volume is larger. The temperature dependence of the magnetic susceptibility shows a cusp-like anomaly at 45 K, and the spontaneous magnetization appears below 33 K. We have measured the Mossbauer spectra of 57 Fe 3+ ( S =2/5) ions, and revealed an anomalous fluctuation of the hyperfine field.

We report a 205 Tl NMR study of vortex state for an oriented polycrystalline sample of an overdoped high- T c superconductor Tl 2 Ba 2 CuO 6+δ ( T c ∼85 K) with magnetic field 2 T along the c -axis. An obvious Redfield pattern of the 205 Tl NMR spectrum for our sample at T =5 K indicates the vortex lattice state without local antiferromagnetic order at vortex cores. We emphasize that nonexponential nuclear spin-lattice relaxation curves indicate an imperfect vortex lattice or Bragg glass phase.

High field ESR measurements of the one dimensional (1D) spin gap system Pb 2 V 3 O 9 have been performed in the frequency region from 120 to 364 GHz in order to examine the magnetic properties of this compound. In the low temperature region we have observed ESR signals in both the paramagnetic phase and the high field phase above the critical field He'These ESR signals show the characteristic features in each phase, indicating that Pb 2 V 3 O 9 undergoes the field-induced magnetic ordering above H c .

We observed a field-induced magnetic ordering in the quasi one-dimensional antiferromagnetic alternating chain system Pb 2 V 3 O 9 for the first time. The characteristic temperature dependence of t...

Nuclear-magnetic-resonance (NMR) studies were performed in Na0.7CoO2 to investigate its magnetic properties from the microscopic point of view. Na0.7CoO2 is a starting compound of the recently discovered superconductor Na0.35CoO2·1.3H2O, in which Co atoms form a tri- angular structure. Although 23 Na-NMR results show no magnetic anomaly down to 1.5 K, Knight shift ( 23 K) and 23 (1/T1T) of 23 Na continue to increase, suggestive of the vicinity of the magnetic phase. From the relation between 23 K and 23 (1/T1T), it is shown that ferromagnetic fluctuations are dominant below 100 K. In addition to the ferromagnetic correlations, antifer- romagnetic fluctuations are also developed in a low temperature region below 4 K. Magnetic fluctuations suggested by our experiment are discussed. Since the superconductivity in NaxCoO2·yH2O (x � 0.35, y � 1.3) with the transition temperature Tc � 5 K was discovered by Takada et al, 1 understanding of mag- netic properties in the CoO2 plane is one of the most important topics in strongly correlated electron systems. This is because the magnetic properties in the plane might be related to the mechanism of the unconventional superconductivity in the compound. In addition, the Co atoms form a triangular lattice in the plane, which is an- ticipated to possess the geometrical frustrations. Novel types of magnetic transitions and ground states are ex- pected due to a suppression of a long-range magnetic ordering by the geometrical frustrations associated with the triangular structure. In particular, only a few com- pounds have been known to date which possess a metallic property down to the lowest temperature with the geo- metrical frustrations, e.g. (YSc)Mn2 2 and LiV2O4. 3 The NaxCoO2 (0.5 < x < 0.78) compound is considered to be one of the promising metallic compounds with the geometrical frustrations at low temperature. 4 In this paper, we report the magnetic properties in Na0.7CoO2 revealed by our 23 Na-NMR experiments. Powder samples of Na0.7CoO2 were prepared from Na2CO3 (99.99%) and Co3O4(99.9%) by solid-state re- action. Its quality was checked by X-ray powder diffrac- tion. The Na content, which is very sensitive to physical properties, is estimated to be 0.702 by the inductive- coupled plasma atomic emission spectroscopy (ICP- AES) method. Using this well-characterized powder sample, 23 Na- and 59 Co-NMR measurements were per- formed.

We have performed Co-nuclear quadrupole resonance (NQR) studies on Na$_{x}$CoO$_{2}\cdot y$H$_{2}$O compounds with different Na ($x$) and hydrate ($y$) contents. Two samples with different Na contents but nearly the same $T_c$ values ($x$ = 0.348, $T_c$ = 4.7 K ; $x$ = 0.339, $T_c$ = 4.6 K) were investigated. The spin-lattice relaxation rate $1/T_1$ in the superconducting (SC) and normal states is almost the same for the two samples except just above $T_c$. NQR measurements were also performed on different-hydrate-content samples with different $T_c$ values, which were prepared from the same Na-content ($x$ = 0.348) sample. From measurements of $1/T_1$ using the different-hydrate-content samples, it was found that a low-$T_c$ sample with $T_c = 3.9$ K has a larger residual density of states (DOS) in the SC state and a smaller increase of $1/T_1T$ just above $T_c$ than a high-$T_c$ sample with $T_c$ = 4.7 K. The former behavior is consistent with that observed in unconventional superconductors, and the latter suggests the relationship between $T_c$ and the increase in DOS just above $T_c$. This increase, which is seemingly associated with the two-dimensionality of the CoO$_2$ plane, is considered to be one of the most important factors for the occurrence of superconductivity.

The pseudo two-dimensional (2D) magnetic systems (LaS) 1.14 [ M x (NbS 2 ) 2 ] ( M = Mn, Fe, Co) were synthesized for the first time, and their magnetic and transport properties were investigated. (LaS) 1.14 [ M x (NbS 2 ) 2 ] show three-dimensional (3D) magnetic transitions at 4.4, 6.2 and 15 K for M = Mn, Co and Fe, respectively. The 3D transition temperatures are lowered by the quasi-2D magnetic property brought about the insertion of the extra layer LaS to the layered magnets M x NbS 2 , and the 2D short-range order effects are observed in the heat capacity at much higher than the transition temperatures. The minimum behavior of ρ and the maximum behavior of R H appear in the low temperatures. We consider that the weak localization in the quasi-2D transport system causes the anomalous behaviors of the transport properties.

We applied 57 Fe Mossbauer spectroscopy for investigating the Ising spin triangular lattice antiferromagnet (TLA) (CeS) 1.16 [Fe 0.33 (NbS 2 ) 2 ] between 2 and 300 K. The spectra revealed that the relaxation time of the hyperfine field markedly changes in the intermediate phase between T N1 =22 K and T N2 =15 K due to strong spin fluctuation. The relaxation of the hyperfine field is not sufficiently fast as a paramagnet even at 77 K, which is much higher than T N1 , and the inverse susceptibility of (LaS) 1.14 [Fe 0.33 (NbS 2 ) 2 ] deviates from the Curie–Weiss law below 100 K. These results indicate that an unusual short-range order exists above T N1 . The temperature dependence of the Mossbauer spectra can be explained by phase transition of the three-dimensional TLA model with weak interlayer exchange interactions.

We investigated macroscopic and microscopic physical properties of S = 1/2 Mo3 cluster magnets Li2ScMo3O8 and Li2InMo3O8. Li2InMo3O8 shows magnetic ordering at TN 12 K, while no magnetic ordering is observed down to 0.5 K in Li2ScMo3O8 in spite of the strong antiferromagnetic interaction among clusters probed by the Weiss temperature. 115In and 45Sc NMR measurements demonstrate that there should be difference in charge fluctuation in clusters between Li2InMo3O8 and Li2ScMo3O8. Our result suggests that the origin of different ground states realized in Li2InMo3O8 and Li2ScMo3O8 is different condition in charge and local structure as one of characteristics of the cluster magnet.

We investigated the effect of Co substitution in Fe1−x Co x Ga3 by means of electric resistivity and magnetic measurements. Nearly ferromagnetic behaviors were observed in Fe1−x Co x Ga3 system by the chemical substitution of Co for Fe in diamagnetic mother compound FeGa3, accompanying with a semiconducting to metallic transition. With the substitution of Co, the magnetization of Fe1−x Co x Ga3 increases first, and then decreases and finally it becomes diamagnetic. The magnetic properties of Fe1−x Co x Ga3 were analyzed in terms of self-consistent renormalization (SCR) theory and Takahashi's theory. The spin-fluctuation parameters, fourth order expansion coefficients of magnetic free energy (), the magnetic susceptibility in the ground state X(0), the spectral widths of the spin fluctuation spectrum T 0 and Ta in the frequency and wave-number spaces, respectively, were estimated from the parameters derived from magnetic measurements. The magnetic properties of Fe1−x Co x Ga3 can be understood almost quantitatively by the SCR theory and Takahashi's theory of spin fluctuations.

We have investigated the physical properties of the magnetic diluted triangular lattice antiferromagnetic system Li2Sc1-xSnxMo3O8. For all compounds, no mangetic ordering has been observed. On the other hand, the partial spin disappearing behavior is found in all Sn-substituted compounds except x = 0, which has been also observed in the similar magnetic system LiZn2Mo3O8. Considering the relationship between the crystal structure and the magnetism, the partial spin disappearance is properly explained by a formation of the valence bond glass derived from the randomness effect

Magnetic properties of the layered itinerant system ${\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{Co}}_{2}{\mathrm{P}}_{2}$ were investigated under a magnetic field up to 70 T. As for the exchange-enhanced Pauli paramagnetic metal $\mathrm{Sr}{\mathrm{Co}}_{2}{\mathrm{P}}_{2}$, the magnetization curve shows two characteristic anomalies. The high-field anomaly corresponds to an itinerant-electron metamagnetic transition (IEMT), while the low-field one is small and broad without any obvious hystereses just as the crossover phenomenon between different energy states. Such a successive transition in the magnetization curve cannot be explained by the conventional phenomenological theory for IEMT based upon the Landau expansion of the magnetic free energy, but by the extended Landau expansion theory dealing with two distinguishable energy states. In the systematical study on ${\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{Co}}_{2}{\mathrm{P}}_{2}$, furthermore, the metamagnetic transition field decreases and goes to zero as $x$ increases up to 0.5, indicating that the ferromagnetic quantum critical point exists at $x\ensuremath{\sim}0.5$.

We report physical properties of a chromium dichalcogenide 1T-${\text{CrSe}}_{2}$ with tetravalent Cr cations. Interplay between orbital degrees of freedom and the valence instability of Cr is studied by means of magnetic, electrical, electron diffraction, and x-ray diffraction measurements. Associated with the phase transitions, a space group of ${\text{CrSe}}_{2}$ varies from trigonal $P\overline{3}m1$ to rhombohedral $R\overline{3}m$ through monoclinic $I2/m$. By considering behaviors of $\ensuremath{\chi}$ and $\ensuremath{\rho}$ in addition to possible ordering patterns of occupied ${t}_{2g}$ orbitals, we have concluded that the origin of successive phase transitions is simultaneous occurrence of orbital ordering and valence change of Cr through each phase transition.

In order to study the phase diagram from a microscopic viewpoint, we have measured wTF- and ZF-$\mu^+$SR spectra for the Sr$_{1-x}$Ca$_x$Co$_2$P$_2$ powder samples with $x=0$, 0.2, 0.4, 0.5, 0.6, 0.8, and 1. Due to a characteristic time window and spatial resolution of $\mu^+$SR, the obtained phase diagram was found to be rather different from that determined by magnetization measurements. That is, as $x$ increases from 0, a Pauli-paramagnetic phase is observed even at the lowest $T$ measured (1.8~K) until $x=0.4$, then, a spin-glass like phase appears at $0.5\leq x\leq0.6$, and then, a phase with wide field distribution probably due to incommensurate AF order is detected for $x=0.8$, and finally, a commensurate $A$-type AF ordered phase (for $x=1$) is stabilized below $T_{\rm N}\sim80~$K. Such change is most likely reasonable and connected to the shrink of the $c$-axis length with $x$, which naturally enhances the magnetic interaction between the two adjacent Co planes., Comment: 5 pages, 5 figures, conference paper of muSR2014 (accepted for publication)

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.

Low dimensional triangle magnetism was studied for transition metal intercalates of incommensurate misfit layer compounds (RS) x [M 0 33 (NbS 2 ) 2 ] (R = La, Ce, M = Fe, Mn). Magnetization measurements for the single crystals of the Fe intercalated compounds (RS) x [Fe 0.33 (NbS 2 ) 2 ] show the successive magnetic transition at 14 K and 22 K. The strong frustration appears between two transition temperatures as quasi two-dimensional antiferromagnetic triangular Ising spin system. In contrast, the Mn compounds (RS) x [Mn 0 33 (NbS 2 ) 2 ] has very low transition temperature of 3.0 K due to the nature of quasi two-dimensional Heisenberg spin system.

We synthesized the Fe intercalated misfit-layer compounds $(R\mathrm{S}{)}_{x}[{\mathrm{Fe}}_{0.33}({\mathrm{NbS}}_{2}{)}_{2}]$ $(R=\mathrm{L}\mathrm{a},\mathrm{C}\mathrm{e}),$ and investigated their magnetic properties. The intercalated Fe atoms form the $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ superlattice to the ${\mathrm{NbS}}_{2}$ lattice in these compounds, and show the successive magnetic transition at 15 and 22 K. The strong frustration appears between two transition temperatures in their quasi-two-dimensional antiferromagnetic triangular Ising spin system. The temperature dependence of the susceptibility of $(\mathrm{CeS}{)}_{1.16}[{\mathrm{Fe}}_{0.33}({\mathrm{NbS}}_{2}{)}_{2}]$ shows three magnetic transitions at 3.4, 15, and 22 K corresponding to the antiferromagnetic transition of Ce and Fe. This suggests that the magnetic interactions of Ce and Fe occur independently.

The temperature dependence of magnetic susceptibility was measured for the S = 1 2 quasi one dimensional antiferromagnet Pb 2 V 3 O 9 under the steady magnetic field up to μ 0 H = 30 T . This material has alternating exchange interaction and a spin-gap at zero magnetic field. An anomaly of magnetic susceptibility indicating the field-induced antiferromagnetic long-range order was observed in high magnetic fields. The Neel temperature at high fields is much lower than the calculated value based on the standard mean-field theory of field-induced magnetic order.

We report 125Te NMR studies for single crystals of CeTe 3 between 22 and 307 K, under an applied field of H = 7.4847 T along a- or b-axis. The 125Te NMR spectrum consists of superposition of broad and sharp peaks, which are assigned to the signals of 125Te(1) in Te(1) sheets and 125Te(2) in CeTe(2) bi-layers, respectively. The broad 125Te(1) NMR spectrum consists of three distinguishable lines, regarded as an evidence for the presence of the incommensurate charge-density wave (ICDW) modulation. The Knight shifts of 125Te(1) widely distribute from - 0.16 % to + 0.58 % at 110 K and the temperature dependence of each Knight shift is proportional to the bulk susceptibility, indicating that the conduction electron spin density is polarized by the Ce local moments in the CDW state.

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.

We synthesized four series of bilayer hydrated Na x CoO 2 · y H 2 O samples and studied their duration dependences of superconducting transition temperatures T c 's in a high humidity atmosphere. After the long duration of a year, T c of two series of samples decreased gradually down to 2.7 K, while the other series became nonsuperconductors and were partially resolved into CoOOH. The difference in the duration dependence of superconductivity is ascribed to the difference in an initial content of Na, which results from the reduction during immersing water. A monotonic relation between the superconducting volume fraction and T c suggests an unconventional superconducting mechanism, similarly to high- T c cuprates.

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.

Na 23 NMR was measured for newly synthesized superconducting and non-superconducting bilayer-hydrated (BLH) Na x CoO 2 · y H 2 O compounds systematically prepared by time-controlling duration-effect method of the sample preparation in high humidity atmosphere. The nuclear spin-lattice relaxation rate 1 / T 1 of Na 23 shows a ferromagnetic power-law behavior ( T 0.7 ) for both superconducting and non-superconducting BLH compounds in the low temperature regime, which has been also observed in Na 0.7 CoO 2 , while the order of amplitude of 1 / T 1 is substantially suppressed in BLH cases. Therefore, the in-plane ferromagnetic fluctuation still remains after the intercalation of water molecules although the inter-plane antiferromagnetic correlation is weakened, suggesting that the superconductivity occurs in the vicinity of the quantum critical point of the A-type spin fluctuations in the phase diagram of the novel Na x CoO 2 · y H 2 O system.

We present site-selective Zeeman-perturbed plane-site 63Cu(2) NQR studies of vortex cores in the dilute magnetic flux lattice of oriented powder YBa 2 Cu 3 O 7 - δ ( T c = 92 K ) at a magnetic field of 96 mT along the c -axis. The local spin correlation around the vortex cores near a lower critical field H c 1 was found to be moderately enhanced, in contrast to the strongly enhanced local spin correlation around the in-plane non-magnetic impurities Zn.

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.

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.

The presence of antiferromagnetic (AF) order seems to be a common feature for the parent compounds of cuprate as well as some pnictide high-temperature superconductors. In order to search for antiferromagnetic order in the closely related rare-earth cobalt arsenic oxides ($R$CoAsO), we have measured muon-spin rotation and relaxation (${\ensuremath{\mu}}^{+}$SR) spectra on a series of powder samples with $R=\text{La}$, Ce, Pr, Nd, Sm, and Gd. It was found that, besides GdCoAsO, all the other five compounds enter into a static ferromagnetic ordered phase below around 70 K ($=\phantom{\rule{-0.16em}{0ex}}{T}_{\mathrm{C}}$), while additional transitions into a static AF ordered phase were found for NdCoAsO and SmCoAsO. For GdCoAsO, a static ferrimagnetic phase appeared below 60.5 K and then an incommensurate spin-density-wave ordered phase followed below 3.2 K. The AF spin structure was also found to strongly depend on $R$.

A large magnetoresistance (MR) effect was observed in the layered compounds NdCoAsO and SmCoAsO, in which ferromagnetically ordered itinerant-electrons of Co are sandwiched by localized 4$f$-electrons of $Ln^{3+}$, below ferromagnetic-antiferromagnetic transition (FAFT) temperature $T_\mathrm{N}$ as observed in other FAFT compounds. In SmCoAsO, the large MR effect is also observed up to the Curie temperature $T_\mathrm{C}$, and it is found to be originating in the presence of another antiferromagnetic phase in the low-magnetic field region of the ferromagnetic phase.

Intrinsic spin susceptibility of the novel layered superconducting and magnetic system Fe1+δTe1−xSex was investigated by means of the magnetization measurements in comparing with the 125Te NMR Knight shift 125K. The macroscopic uniform susceptibility in Fe1+δTe1−xSex consists of the itinerant magnetization originated in the Fe(1) site, localized one in the Fe(2) site and the ferromagnetic‐like impurity which is frequently sandwiched by the thin film‐like single crystals. Unlike the macroscopic magnetization, Knight shift 125K is mainly attributed to the itinerant magnetism of the Fe(1) site, which is important for the superconductivity and the magnetism in the Fe1+δTe1−xSex system. The magnetic susceptibility estimated in the high‐field region agrees well with 125K. The uniform susceptibility of the superconducting Fe1+δTe1−xSex gradually decreases with decreasing temperature in the normal state accompanied by the growth of antiferromagnetic spin afluctuations.