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In order to clarify the carrier density dependence of the microscopic magnetic nature in ${\text{Na}}_{x}{\text{CoO}}_{2}\ensuremath{\cdot}y{\text{H}}_{2}\text{O}$, we have performed a positive muon-spin rotation/relaxation $({\ensuremath{\mu}}^{+}\text{SR})$ study of ${\text{H}}_{2}\text{O}$ and ${\text{D}}_{2}\text{O}$ intercalated samples. Based on the zero-field (ZF) ${\ensuremath{\mu}}^{+}\text{SR}$ measurements, there was no clear difference between the two superconducting phases (SCI and SCII). This is also likely to exclude the exotic scenario for the superconductivity of the SCII phase, in which the superconducting state breaks the time-reversal symmetry of the Cooper pairs, resulting in the appearance of a weak internal magnetic field below ${T}_{c}$. Furthermore, the ZF spectrum for the ${\text{H}}_{2}\text{O}$ intercalated sample exhibits a clear oscillation in the whole $T$ range measured (1.4--100 K), suggesting the formation of ``${[{\text{H}}_{3}\text{O}]}^{+}$-like'' ${\text{H}}_{2}{\ensuremath{\mu}}^{+}\text{O}$ ions in the sample. The absence of the oscillation in the ${\text{D}}_{2}\text{O}$-intercalated sample also evidences the presence of the ${\text{H}}_{2}{\ensuremath{\mu}}^{+}\text{O}$ complex. Considering the fraction of the ${\text{H}}_{2}{\ensuremath{\mu}}^{+}\text{O}$ signal, we have demonstrated the coexistence of ${[{\text{H}}_{3}\text{O}]}^{+}$ ions and ${\text{H}}_{2}\text{O}$ in this compound.

We synthesized a polycrystalline sample of SmCoAsO and measured its magnetization $(M)$ at various of temperatures $(T)$ and magnetic fields $(H)$. As decreasing $T$, a paramagnetic to ferromagnetic transition occurs at 70 K, and then a ferromagnetic to antiferromagnetic transition occurs at 42 K. In the antiferromagnetic phase, we observed the behavior characteristic of metamagnetic transitions in $M\text{\ensuremath{-}}H$ curves. From the results of magnetization measurements up to $H=56\text{ }\text{T}$, we successfully draw the magnetic phase diagram of SmCoAsO. We observed convex behavior in Arrott plots in the ferromagnetic temperature region as seen in MnSi, ${\text{Fe}}_{1\ensuremath{-}x}{\text{Co}}_{x}\text{Si}$, and isostructural compound LaCoAsO. We discussed the magnetic property of SmCoAsO above ${T}_{\text{C}}$ based on the spin-fluctuation theory.

Macroscopic physical properties of the novel layered superconducting system ${\text{Fe}}_{1+\ensuremath{\delta}}{\text{Te}}_{1\ensuremath{-}x}{\text{Se}}_{x}$ were investigated by means of magnetic-susceptibility, electric resistivity, and heat-capacity measurements. In addition to the substitution effect of the Te site, intercalated excess irons would suppress the bulk superconductivity. We have also performed $^{125}\text{T}\text{e}$ and $^{77}\text{S}\text{e}$ NMRs on a single crystal of ${\text{Fe}}_{1.04}{\text{Te}}_{0.67}{\text{Se}}_{0.33}$ with the highest superconducting transition temperature ${T}_{\text{c}}\ensuremath{\sim}14\text{ }\text{K}$. In the superconducting state, the spin part of Knight shifts for both $H\ensuremath{\parallel}a$ and $H\ensuremath{\parallel}c$ are suppressed, and the nuclear-spin-lattice relaxation rate $1/{T}_{1}$ shows the power-law like behavior without any coherent peaks, indicating the nodal spin-singlet superconductivity. In the normal state, $1/{T}_{1}T$ is enhanced by antiferromagnetic spin fluctuations with decreasing temperature. The superconductivity in ${\text{Fe}}_{1+\ensuremath{\delta}}{\text{Te}}_{1\ensuremath{-}x}{\text{Se}}_{x}$ is realized in the vicinity of the magnetic quantum phase transition and is possibly mediated by the growth of the antiferromagnetic spin fluctuations.

Carbon-intercalation effects on weakly ferromagnetic ${\text{Ni}}_{3}\text{Al}$ have been studied by $^{27}\text{A}\text{l}$ spin-echo NMR techniques. The Knight shift $K$ and the nuclear spin-lattice relaxation time ${T}_{1}$ of $^{27}\text{A}\text{l}$ have been measured in the carbon-intercalated ${\text{Ni}}_{3}{\text{AlC}}_{x}$ with $x=0$, 0.01, 0.02, 0.05, and 0.1, whose Curie temperatures are 36 K, 18 K, $l2\text{ }\text{K}$, $l2\text{ }\text{K}$ and $l2\text{ }\text{K}$, respectively. The magnitude of the negative $^{27}\text{A}\text{l}$ hyperfine coupling constants were found to decrease at first, and then increase with the carbon intercalation into the body-center site of ${\text{Ni}}_{3}\text{Al}$. The linear relations between the $1/{T}_{1}T$ and the magnetic susceptibility $\ensuremath{\chi}$ indicate that the three-dimensional ferromagnetic spin fluctuations are dominant in the ${\text{Ni}}_{3}{\text{AlC}}_{x}$ system. We estimate the evolution of the characteristic temperature of spin fluctuations, ${T}_{0}$, in frequency space when the system changes from weak ferromagnetism to a nearly ferromagnetic state. Then, we analyze the temperature dependence of inverse magnetic susceptibilities and discuss the feature of the spin fluctuations in this system. As a result, the carbon-intercalation effect was found to be over a long range, inducing three-dimensional ferromagnetic quantum phase transition at $x\ensuremath{\sim}0.02$.

Pb2V3O9 was found to have antiferromagnetic alternating chains of S=1/2 and show the antiferromagnetic long range ordered (AFLRO) state under the magnetic field between 4 and 38 T. We succeeded in growing single crystals of Pb2V3O9 by floating zone method and determined the asymmetric H-T phase diagram of Pb2V3O9 from measurements of the magnetization and the heat capacity. Previous reports focused on the AFLRO state in the low magnetic field region and that in high magnetic field region was not discussed so much. In this paper, we examined the AFLRO state in terms of the mean field theory and the picture of Bose-Einstein condensation of magnons to discuss the whole phase diagram. Consequently, the asymmetry of the phase boundary in Pb2V3O9 is explained by the mixing contribution of excited states and by interchain interactions., Comment: 14 pages, 14 figures

We present our NMR studies of double-layer hydrated cobalt oxides NaxCoO2-yH2O (x ~ 0.35, y ~ 1.3) with various Tc = 0 - 4.8 K and magnetic transition temperatures. High-resolution $^{1}$H NMR spectrum served as an evidence for the existence of H$_{3}$O$^{+}$ oxonium ions. $^{23}$Na nuclear spin-lattice relaxation rates served to detect local field fluctuations sensitive to Tc. $^{59}$Co nuclear quadrupole resonance (NQR) spectra served to classify the various Tc samples. From the classification by $^{59}$Co NQR frequency, the double-layer hydrated compounds were found to have two superconducting phases closely located to a magnetic phase. In the normal state and at a magnetic field in the $ab$-plane, two $^{59}$Co NMR signals with different Knight shifts and different $^{59}$Co nuclear spin-lattice relaxation times $^{59}T_{1}$ were observed. The two $^{59}$Co NMR signals suggest magnetic disproportionation of two Co sites or in-plane (XY) anisotropy of a single Co site. Non Korringa behavior and power law behavior in zero-field NQR 1/$^{59}T_{1}$ above and below Tc suggest non-Fermi liquid and unconventional superconductivity.

We report 7Li NMR studies of single crystals of triangular-lattice Heisenberg antiferromagnet Li7RuO6. Slow critical divergence with a wide critical region of |T/TN - 1|< 7 was observed in 7Li nuclear spin-lattice relaxation rate. The slowing down of staggered spin fluctuations was analyzed in a renormalized classical region of a two-dimensional triangular-lattice non-linear sigma model. A spin stiffness constant was found to reduce to about 20 % from the value in a spin-wave approximation. The effect of spin frustration, e.g., Z2 vortex excitations on the critical phenomena is suggested., 4 pages, 5 figures, the references were updated, to be published in J. Phys. Soc. Jpn. 78 (2009) No.2

59Co NQR studies of low frequency spin fluctuations of double‐layer hydrated triangular‐lattice superconductors and nonsuperconductors NaxCoO2−yH2O are presented. For all the samples, 59Co nuclear spin‐lattice relaxation rates 1/59T1 indicated non‐Korringa behaviors in the normal states. For the nonsuperconductor, 1/59T1 indicated a magnetic critical slowing down effect. The triangular‐lattice superconductivity emerges near a magnetic instability.

Co nuclear magnetic resonance (NMR) measurements are performed on superconducting ${\mathrm{Na}}_{x}{({\mathrm{H}}_{3}\mathrm{O})}_{z}\mathrm{Co}{\mathrm{O}}_{2}∙y{\mathrm{H}}_{2}\mathrm{O}$ with a bilayered hydrate structure. External fields are applied exactly parallel to the $\mathrm{Co}{\mathrm{O}}_{2}$ plane on a high-quality powdered sample, which is aligned in a strong magnetic field. When superconductivity is suppressed by external magnetic fields, the nuclear spin-lattice relaxation rate divided by temperature $(1∕{T}_{1}T)$ continues to increase down to ${T}_{c}(H)$, which is the superconducting transition temperature under a magnetic field $H$. From the analyses of the temperature variation, it was found that a sample with ${T}_{c}\ensuremath{\sim}4.8\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, which is the maximum ${T}_{c}$, possesses magnetic fluctuations with a quantum critical character. This suggests the intimate relationship between superconductivity and quantum critical fluctuations in the hydrate cobaltate. We determined ${T}_{c}(H)$ and constructed the ${H}_{c2}\ensuremath{-}{T}_{c}$ phase diagram from the present NMR measurements. The field dependence of ${T}_{c}(H)$ is discussed.

We report $^{125}\mathrm{Te}$ NMR studies for single crystals of $\mathrm{Ce}{\mathrm{Te}}_{3}$ between 10 and $307\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, under an applied field of $H=7.4847\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ along the $a$ or $b$ axis $H\ensuremath{\Vert}ab$ and the $c$ axis $H\ensuremath{\Vert}c$, respectively. We observed that the $^{125}\mathrm{Te}$ NMR spectra consist of a superposition of broad and sharp peaks, which we assign to the signals of $^{125}\mathrm{Te}(1)$ in double Te(1) sheets and $^{125}\mathrm{Te}(2)$ in CeTe(2) bilayers, respectively. For $H\ensuremath{\Vert}ab$, a broad $^{125}\mathrm{Te}(1)$ NMR spectrum shows a powder pattern with three split lines, which is evidence for an incommensurate charge-density wave modulation. The $^{125}\mathrm{Te}(1)$ NMR spectrum with three lines broadens with cooling. Knight shifts widely distributed from $\ensuremath{-}0.16%$ to $+0.58%$ at $110\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ indicate that a spin density of conduction electron is polarized from Ce local moments. For $H\ensuremath{\Vert}c$, a spectrum has a fine structure with three lines, and the linewidth of the $^{125}\mathrm{Te}(1)$ NMR spectrum is narrow compared with that for $H\ensuremath{\Vert}ab$. On the other hand, the anisotropic Knight shift of the $^{125}\mathrm{Te}(2)$, which is located at the CeTe(2) bilayer, is positive with proportion to the anisotropic bulk susceptibility for $H\ensuremath{\Vert}ab$ and $H\ensuremath{\Vert}c$. The hyperfine coupling constants of $^{125}\mathrm{Te}(2)$ are nearly isotropic but the nuclear spin-lattice relaxation rate is strongly anisotropic, indicating the anisotropic spin fluctuations in this system. The nuclear spin-lattice relaxation rate of the $^{125}\mathrm{Te}(2)$ diverges due to the slowing down of spin fluctuations.

We report on the anion substitution and pressure effects on the layered compound 1T-CrSe2 with unusual-valent chromium. Owing to the competition between the orbital degrees of freedom and the valence instability of Cr4+, the systems of Cr(Se1−xSx)2 and Cr(Se1−yTey)2 exhibit several types of phase transition. As well as the parent compound CrSe2, Te-substituted samples and slightly S-substituted samples of x ≤ 0.025 show two phase transitions, which are likely to be related to both the valence change and orbital ordering of Cr4+. The highly S-substituted samples of x > 0.04 show one phase transition, which can be attributed to orbital ordering without a valence change. The intermediate S-substituted samples of \(0.025 < x \lesssim 0.04\) exhibit the above three types of phase transition and, in addition, another type of transition. In contrast, the pressure effect on CrSe2 is qualitatively different from these anion substitution effects, which indicates that these anion substitution effects are not simply ...

We report the magnetic properties of Sr- and Bi-substituted samples of the one-dimensional alternating $S=1∕2$ spin chain compound ${\mathrm{Pb}}_{2}{\mathrm{V}}_{3}{\mathrm{O}}_{9}$. In the Sr-substituted system, we obtained two series of samples synthesized by different heat treatments; one series shows the reduction of the spin gap without antiferromagnetic long-range order (AF-LRO) and the other shows AF-LRO at low temperatures. We also observed impurity-induced AF-LRO in the Bi-substituted system. The fitting results of magnetic susceptibilities imply the possible coexistence of a spin gap and AF-LRO in both AF-LRO systems. These observations of AF-LRO with a small amount of substitution indicate that the magnetic instability involving a quantum critical point is inherent in the spin-gap system ${\mathrm{Pb}}_{2}{\mathrm{V}}_{3}{\mathrm{O}}_{9}$.

Co nuclear quadrupole resonance (NQR) measurements were performed on several superconducting (SC) NaxCoO2⋅yH2O samples with different values of a SC transition temperature (Tc). The measurements were done for the investigation of the relationship between Tc and microscopic physical quantities derived from the Co NQR. We measured Co‐NQR frequency νQ and the nuclear‐lattice relaxation rate 1/T1 the Co site, and found the relationship between νQ and the value of 1/T1T at Tc: the higher‐Tc sample possesses the higher νQ and larger value of 1/T1T at Tc. When νQ exceeds a critical value (∼12.45 MHz), magnetic ordering was observed. A possible phase diagram in NaxCoO2⋅yH2O is proposed, in which the NQR frequency νQ is the tuning parameter and determines the ground states. In this phase diagram, the SC phase is adjacent to the magnetic phase, suggesting that the superconductivity is intimately related to magnetic fluctuations. We found the coexistence of the superconductivity and the magnetic ordering in the same...

We report 23Na NMR studies of the polycrystalline samples of double-layer hydrated cobalt oxides NaxCoO2.yH2O (x ~ 0.35 and y ~ 1.3) with the superconducting transition temperatures Tc < 1.8K and ~4.5K, and the dehydrated NaxCoO2 (x ~ 0.35). The hyperfine field and the electric field gradient at the Na sites in the non-hydrated Na0.7CoO2 and the dehydrated Na0.35CoO2 are found to be significantly reduced by the hydration, which indicates a strong shielding effect of the intercalated water molecules on the Na sites. The temperature dependence of 23 Na nuclear spin-lattice relaxation rate 1/23T1 of the non-superconducting double-layer hydrate NaxCoO2.yH2O is found to be similar to that of the non-hydrated Na0.7CoO2, whose spin dynamics is understood by A-type (intra-layer ferromagnetic and inter-layer antiferromagnetic) spin fluctuations. The superconducting phase is located close to the quantum critical point with the A-type magnetic instability., 4 pages, 4 figures

We succeeded in synthesizing the powder samples of bilayer-hydrate sodium cobalt oxide superconductors NaxCoO2-yH2O with Tc = 0 ~ 4.6 K by systematically changing the keeping duration in a 75 % relative humidity atmosphere after intercalation of water molecules. From the magnetic measurements, we found that the one-day duration sample does not show any superconductivity down to 1.8 K, and that the samples kept for 2 ~ 7 days show superconductivity, in which Tc increases up to 4.6 K with increasing the duration. Tc and the superconducting volume fraction are almost invariant between 7 days and 1month duration. The 59Co NQR spectra indicate a systematic change in the local charge distribution on the CoO2 plane with change in duration., 4 pages, 5 figures, submitted to Journal of the Physical Society of Japan

The Co Knight shift was measured in an aligned powder sample of Na_xCoO_2yH_2O, which shows superconductivity at T_c \sim 4.6 K. The Knight-shift components parallel (K_c) and perpendicular to the c-axis (along the ab plane K_{ab}) were measured in both the normal and superconducting (SC) states. The temperature dependences of K_{ab} and K_c are scaled with the bulk susceptibility, which shows that the microscopic susceptibility deduced from the Knight shift is related to Co-3d spins. In the SC state, the Knight shift shows an anisotropic temperature dependence: K_{ab} decreases below 5 K, whereas K_c does not decrease within experimental accuracy. This result raises the possibility that spin-triplet superconductivity with the spin component of the pairs directed along the c-axis is realized in Na_xCoO_2yH_2O., Comment: 5 pages, 5 figures, to be published in Journal of Physical Society of Japan vol. 75, No. 1

The magnetic properties of $R{\mathrm{Te}}_{3}$ $(R=\mathrm{Ce},$ Pr, Nd, Gd, Dy), which has a structure consisting of the alternate stacking of one $R\mathrm{Te}$ layer and two Te layers, were investigated using magnetization and electrical resistivity measurements. The magnetic transition temperatures were found at 3.0 K for $R=\mathrm{Ce},$ 3.2 K for Nd, 11.5 K for Gd, and 4.5 K for Dy, respectively, and the Pr compound showed van Vleck paramagnetism. The ordered magnetic moment of $R{\mathrm{Te}}_{3}$ lies within the layer. In contrast, the ordered magnetic moments of $R{\mathrm{Te}}_{2},$ having alternate stacking of one $R\mathrm{Te}$ and one Te layer, point to the layer-stacking direction, although the point symmetry at the R site and the coordination of the Te atoms to the R atoms are almost the same. The difference of the magnetic anisotropy in $R{\mathrm{Te}}_{2}$ and $R{\mathrm{Te}}_{3}$ was discussed in terms of the effective charge of the Te atoms in the Te layer with an electron charge transferred from the $R\mathrm{Te}$ layer. We propose magnetic compounds designed by charge introduction based on this result.

We report 59Co NMR studies on the magnetically oriented powder samples of Co-oxide superconductors NaxCoO2yH2O with Tc ~ 4.7 K. From two-dimensional powder pattern in the NMR spectrum, the ab-plane Knight shift in the normal state was estimated by the magnetic field dependence of second-order quadrupole shifts at various temperatures. Below 50 K, the Knight shift shows a Curie-Weiss-like temperature dependence, similarly to the bulk magnetic susceptibility chi. From the analysis of so-called K-chi plot, the spin and the orbital components of K and the positive hyperfine coupling constant were estimated. The onset temperature of superconducting transition in the Knight shift does not change so much in an applied magnetic field up to 7 T, which is consistent with the reported high upper critical field Hc2. The Knight shift at 7 T shows an invariant behavior below Tc. No coherence peak just below Tc was observed in the temperature dependence of the nuclear spin-lattice relaxation rate 1/T1 in both cases of NMR and NQR. We conclude that the invariant behavior of the Knight shift below Tc and unconventional behaviors of 1/T possibly indicate the spin-triplet superconductivity with p- or f-wave symmetry., Comment: 17 pages, 10 figures. Extended version

In cobaltate superconductor Na x (H 3 O) z CoO 2 . yH 2 O with bilayered hydrate (BLH) structure, Co nuclear magnetic resonance (NMR) measurement was performed to investigate the low-temperature magnetic excitations in magnetic field. The nuclear spin-lattice relaxation rate (1/T 1 ) of Co was measured in the field range of 1.5-14T parallel to the CoO 2 plane. In the normal state, 1/T 1 T follows the temperature dependence expressed as 1/T 1 T ∞ I/√T-θ in all the field range. At the field lower than 10T, 1/T 1 T continues to increase down to T c and decrease due to superconductivity below T c . T 1 T = Const. behavior is not observed at all above T c . When the field is higher than 10 T, I/T 1 T does not show clear decrease, but stop increasing below Τ*. Using T c and Τ* we determine, a H-T phase diagram is developed. The field dependence of T c at low fields is as small as dT c /dH ∼ -0.06 K/T. A novel phase characterized by a small kink of 1/T 1 T seems to be present at high-field region above 10T.

We measured 23 Na -NMR spectra and nuclear spin-lattice relaxation rates 23 ( 1 / T 1 ) of superconducting and non-superconducting bilayer hydrates Na x CoO 2 · y H 2 O ( x ∼ 0.3 , y ∼ 1.3 ). The central resonance frequencies show small but various shifts due to differences in the shielding effect by intercalated H 2 O molecules. The different shielding effect also gives a large difference in the magnitude of 23 ( 1 / T 1 ) .

We studied the vortex state of an oriented polycrystalline high- T c superconductor Tl 2 Ba 2 CuO 6 + δ ( T c ∼ 85 K ) by Tl 205 NMR spin-echo technique. Although more than 10 years have passed since the sample was synthesized, no aging effects were found in the low-field magnetic susceptibility and the zero-field Cu 63 , 65 nuclear quadrupole resonance spectrum. From Tl 205 NMR spectra at 2 T, we observed vortex melting, vortex partial melting, imperfect vortex lattices, and the absence of static antiferromagnetic ordering at vortex cores.

Pb 2 V 3 O 9 is a quasi-one-dimensional spin-gapped Mott insulator and exhibits a magnetic field-induced antiferromagnetic ordering together with the Bose–Einstein condensation (BEC) of triplons. In order to study impurity effects on BEC of triplons, we synthesized Sr-substituted samples for Pb sites. We found that the two types of samples suffered by different heat treatments at 600 and 650 ∘ C show different magnetic properties. From the temperature dependence of the magnetic susceptibility, we observed the reduction of a spin-gap and the impurity-induced antiferromagnetic ordering for 600 ∘ C series and 650 ∘ C series, respectively. Since Pb 2 V 3 O 9 has two crystallographic Pb sites, it might be due to the fact that the Sr occupation sites can be changed by the heat treatment.

Successive phase transition of the cubic ( F 4 ¯ 3 m ) compound GeV 4 S 8 has been studied by the magnetic susceptibility, the specific heat and the neutron diffraction experiments. In the temperature dependences of the susceptibility and the specific heat, two anomalies have been observed at T S = 33 and T N = 18 K . Sharp peaks in the specific heat at T S and T N indicate that both transitions are of the first order. The neutron diffraction revealed that, GeV 4 S 8 undergoes successive structural phase transitions from cubic to rhombohedral (R3m) at T S , and to orthorhombic (Imm2) at T N with the decrease of temperature. Consequently, the antiferromagnetic ordering at T N is found to be accompanied with the structural transition.

We have performed Co nuclear quadrupole resonance (NQR) measurements in various bilayered-hydrate (BLH) Na x CoO 2 · y H 2 O compounds, showing superconducting (SC) and non-SC characteristics. A weak magnetic order was found in a BLH sample with a longer c -axis lattice parameter. We also found that the NQR frequency ν Q arising from the ± 7 2 ↔ ± 5 2 transition is related to the ground state of this system. A phase diagram is developed, in which the superconducting and magnetic-order temperature T c and T M are plotted with respect to ν Q .

The field-swept nuclear magnetic resonance (NMR) spectra of 59Co in the superconductor Na 0.35 CoO 2 · 1.3 H 2 O have been measured at several magnetic fields below T c . The anisotropic Knight shift K y seems to decrease with decreasing temperature without broadening of the spectrum, indicating either the site-selective diamagnetic effect, which may result in the spin-triplet superconductivity, or the decrease of the intrinsic spin shift. Analysis of the magnetic field dependence of the Knight shift at 2 K revealed that the superconductivity occurs in an unconventional way.

We have successfully synthesized a single-crystal sample of the layered structure ferromagnet Fe3GeTe2 and present the results of its complete characterization using powder X-ray diffraction (XRD), magnetic susceptibility χ(T), isotherm magnetization \(M(H)\), specific heat \(C(T)\), and electrical resistivity ρ(T) measurements. The rietveld refinement of the powder XRD data confirms that Fe3GeTe2 crystallizes in the space group \(p6_{3}/mmc\). The χ(T), \(C(T)\), and ρ(T) data indicate bulk ferromagnetic ordering at \(T_{\text{C}} = 220\) K with a saturation moment of 1.625 µB/Fe at zero temperature. The magnetic measurements of the external magnetic field \(H\) applied along the \(c\)-axis and \(ab\)-plane show a large anisotropy in this material. We found that the modified Arrott plot (\(M^{4}\)–\(H/M\)) rather than the \(M^{2}\)–\(H/M\) plot is obeyed in this material. The generalized Rhodes–Wohlfarth ratio indicates an itinerant magnetism in this material. The spin fluctuation parameters are estimate...

We investigated five \(S = 1/2\) (Ti3+) double perovskite fluorides of the form \(A_{2}B\)TiF6 (\(A\) = \(K\), Rb, Cs; \(B\) = Na, K, Rb; \(A \neq B\)). All five compounds are cubic at room temperature and show various phase transitions at low temperatures, depending on lattice instability. Rb2NaTiF6 shows a Jahn–Teller distortion at 24 K. For Cs2RbTiF6 and Rb2KTiF6, structural transitions with octahedral rotations are observed at 115 and 230 K, respectively. In contrast, K2NaTiF6 shows successive structural transitions at 170 and 110 K. Moreover, Cs2KTiF6 exhibits a unique phase transition at 12 K, which is a result of the competition among the Jahn–Teller effect, lattice instability, and spin frustration. At high temperatures, all have the negative Curie–Weiss temperature \(\theta_{\text{CW}}\simeq -40\) K, indicating dominant antiferromagnetic interactions. At low temperatures, \(g\)-factors decrease and \(\theta_{\text{CW}}\) reaches about 0 K, although all five compounds have different low-temperatur...

We synthesized polycrystalline samples of layered compounds LnCoAsO (Ln = La - Gd) and measured magnetization of the samples, especially, in the cases of Ln = Nd, Sm and Gd, which show ferromagnetic-antiferromagnetic transitions (FAFT). From the results of magnetic measurements, we successfully draw the magnetic phase diagrams of these compounds. We showed that the FAFT temperatures TN at various magnetic fields in the cases of Ln = Nd and Sm well scale to the de Gennes factors of the trivalent ions of Nd and Sm, showing that the Ruderman-Kittel-Kasuya-Yoshida interaction is the origin of the FAFT in these compounds. We also draw the total magnetic phase diagram of LnCoAsO (Ln = La - Gd).

We successfully synthesized a new ternary compound La3Ru4Al12 using an arc-melting technique and systematically measured magnetization of a series of ternary compounds RE3Ru4Al12 (RE = La-Nd). X-ray diffraction results demonstrated that all RE3Ru4Al12 possess the same crystal structure with space group P63/mmc . La3Ru4Al12 and Ce3Ru4Al12 showed paramagnetic behaviors in magnetization, while Pr3Ru4Al12 and Nd3Ru4Al12 showed a ferromagnetic ordering at about 40 K. Their Curie temperatures TC were carefully estimated from so-called Arrott plots.

We successfully synthesized the single crystal of the itinerant ferromagnetic compound La12Fe57.5As41 by Sn-flux method and studied its magnetic properties by magnetization measurements. The temperature dependence of magnetic susceptibility obeys the modified Curie-Weiss law, χ−1 = (χ0 + C/(T − θ))−1, quite well in the high temperature region. The effective moment Peff and the Weiss temperature θ are estimated to be 1.13 μB/Fe and 128.5 K, respectivelly. The magnetization of La12Fe57.5As41 shows the convex behavior when plotted in a form of M2 vs H/M at low temperatures, while the M4 shows the linear relation against H/M in a wide temperature range near TC.

We synthesized single crystals of NH4CuPO4 H2O by a chemical reaction in aqueous solutions. Magnetization and specific heat are well reproduced by a dimer model, and NH4CuPO4 H2O does not show any field-induced magnetic phase transitions. The interdimer interactions would be too weak to observe field-induced phase transitions.

We study the normal state properties of a noncentrosymmetric superconductor Mo 3 Al 2 C by means of the nuclear magnetic resonance (NMR) experiment. The change of NMR line shape and the peak of the nuclear spin-echo decay rate at ≃130 K indicate that the Mo 3 Al 2 C exhibits the phase transition prior to the emergence of superconductivity. The reduction in the conduction electron density is inferred from the decrease in the nuclear spin–lattice relaxation rate. By considering the result of the energy band calculation, we discussed the nature of the newly found phase transition.

Temperature dependences of the electrical resistivity, magnetic susceptibility and specific heat have been measured on the single crystal Ca 3 Ir 4 Sn 13 . This compound shows a bulk superconducting transition at ≈7.0 K. We observe peak-like anomalies, which are attributed to the ferromagnetic spin-fluctuations, in susceptibility and resistivity. The resistivity shows a non Fermi-liquid behavior as ρ=ρ 0 + A * T n ( n =1.2 for H =0) in normal state at low temperatures, and develops into a Fermi-liquid behavior by the suppression of the ferromagnetic spin fluctuation on increasing magnetic fields ( n =2 for H =14 T). The superconductivity disappears for magnetic field H ≥7 T as well as the diminution of the ferromagnetic spin fluctuations. We find that the superconductivity coexists with the ferromagnetic spin fluctuations and seems to cooperate in this material. The large values of Δ C /γ n T c =2.78, Kadowaki–Woods ratio A /γ n 2 =1.14×10 -5 µΩ·cm (K·mol/mJ) 2 and Wilson ratio R w =π 2 k B 2 χ p /3µ B 2 ...

The spin-fluctuation effect in the Se-substituted single crystalline Fe 1+δ Te 1- x Se x ( x = 0, 0.05, 0.12, 0.20, 0.30, 0.33, 0.45, and 0.48; 0≤δ≤0.12) and the polycrystalline Fe 1.11 Se has been studied by the measurements of the X-ray diffraction, the magnetic susceptibility under high magnetic fields and the electrical resistivity under magnetic fields up to 14 T. The samples with x = 0.05, 0.12, 0.20, 0.30, 0.33, 0.45, and 0.48 show superconducting transition temperatures in the ranger of 10–14 K. We obtained their intrinsic susceptibilities by the Honda–Owen method. A nearly linear-in- T behavior in magnetic susceptibility of Se-rich superconducting samples was observed, indicating the antiferromagnetic spin fluctuations have a strong link with the superconductivity in this series. The upper critical field µ 0 H c2 orb for T →0 was estimated to exceed the Pauli paramagnetic limit. The Kadowaki–Woods and Wilson ratios indicate that electrons are strongly correlated in this system. Furthermore, the s...

The structural and magnetic properties of Li 7 RuO 6 were investigated in single crystals. This ruthenate is composed of quasi-two-dimensional distorted triangular lattices of RuO 6 octahedra isolated from each other. Because of the ( t 2 g ) 3 electron configuration of Ru 5+ , a Heisenberg-type magnetic behavior of S =3/2 spins is expected. The magnetic susceptibility reveals an antiferromagnetic transition at T N =6.5 K, much lower than the absolute value of the Weiss temperature Θ=-75 K, indicating a strong geometric frustration. The small and almost isotropic drop of the susceptibility below T N suggests a helical magnetic structure. Specific heat revealed an additional phase transition at T ' N =12 K, suggesting an unconventional magnetic phase diagram.

The Si-intercalated compounds Ni 3 AlSi x ( x = 0, 0.01, 0.02, 0.05, 0.07, and 0.1) and Si substituted compounds Ni 3 Al 1- y Si y ( y = 0, 0.01, 0.015, 0.02, 0.04, 0.06, 0.1, and 0.2) were synthesized and investigated by macroscopic and microscopic magnetic measurements. We found that the common features to these two systems are: (i) drastic disappearance of ferromagnetism in Ni 3 Al with only a small Si concentration x c ≃0.01 or y c ≃0.02, (ii) T 4/3 -temperature dependences in both square spontaneous magnetization M (0, T ) 2 and inverse initial susceptibility χ 0 -1 near the Curie temperature T C for ferromagnetic metal. T 4/3 -temperature dependence of χ 0 -1 are found to hold even for the paramagnetic metals that are classified as nearly itinerant ferromagnets very close to the ferromagnetic instability. On the other hand, our 27 Al NMR results show that the Si intercalation leads to the changes of the hyperfine coupling constant A hf , the characteristic parameters of spin fluctuations, T 0 and T ...

$^{75}$As and $^{139}$La field-swept NMR spectra were obtained for the novel weakly itinerant ferromagnet LaCoAsO with 2D layered structure above the Curie temperature of 55 K. By analyzing NMR spectra, temperature dependences of Knight shift $K$ and nuclear quadrupole resonance frequency $\nu_Q$ were obtained successfully for each nucleus. We confirmed from the so-called $K$-$\chi$ plots that the macroscopic magnetization of our {LaCoAsO} powder sample is intrinsic and does not contain the contribution from impurity phases. We estimated hyperfine coupling constants from the slope of $K$-$\chi$ plots and compared to that of iron-arsenide superconductor., Comment: 5 pages, 5 figures, published on J. Phys. Soc. Jpn. at Vol.79, pp.054703 (2010).

We report magnetic, calorimetric, and transport properties of an iron-based itinerant electron magnet Fe 3 Mo 3 N. Magnetic susceptibility shows a Curie–Weiss behavior at high temperatures and takes a broad maximum at around 75 K. The absence of magnetic long range order was confirmed by 57 Fe-Mossbauer and neutron diffraction measurements. C / T shows a divergent behavior following -log T at low temperatures and reaches 128 mJ/(f.u.mol K 2 ) at 0.5 K. The deviation from the T 2 power law of resistivity also suggests a non-Fermi-liquid (NFL) behavior. The observed C / T and χ are enhanced compared with the values estimated from the theoretical density of states, suggesting a strong magnetic enhancement. The NFL behaviors indicate that Fe 3 Mo 3 N is one of the ideal systems located in the vicinity of the ferromagnetic quantum critical point.

We report results of our magnetization and resistivity measurements using single crystals of the conductive antiferromagnet PdCrO2 with a layered structure, consisting of alternating stacks of a triangular lattice of Pd1+ and of Cr3+ along the c axis. We confirmed that the magnetic susceptibility is nearly isotropic above TN but becomes slightly anisotropic below TN (χab > χc). These results, combined with previously known facts, indicate that PdCrO2 is a Heisenberg spin system, and the spins lie in a plane containing the c axis below TN (an "easy-axis type" 120° structure). We also found that the resistivity exhibits a highly two-dimensional metallic behavior in the whole measured temperature range with an anisotropy ratio ρc/ρab ≥ 150. Interestingly, despite such a strongly anisotropic conductivity, the inter-Pd-layer hopping and the intra-Pd-layer conductivity are both affected by the localized Cr spins in comparable magnitude. The present results make PdCrO2 a promising candidate for the emergence of the unconventional anomalous Hall effect.

We have measured the high-field magnetization of a quasi-one dimensional S=1/2 chain compound Sb2VO5, which was proposed as a new candidate of the inorganic spin-Peierls (SP) system. The magnetization measured at 4.2 K exhibits a clear inflection at around 23 T, indicating obviously the excitation from a spin singlet ground state to a triplet state. Absence of anomalies in specific heat and X-ray diffraction points to no SP transition, and the analysis of the susceptibility suggests that this compound is an alternating spin chain system.

77Se NMR signals were observed in the metallic and insulating states of the quasi-one-dimensional organic compound (DIETSe)2GaCl4. The 77Se NMR spectra at low temperatures are broadened, indicating the presence of magnetic ordering. The shape of the spectra in the magnetically ordered state is characteristic of the spin density wave (SDW) ordering. The divergent behavior of the temperature dependence of the nuclear spin-lattice relaxation rate suggests that the SDW ordering occurs at about 7 K which is lower than the metal-insulator transition temperature of 12 K.

The itinerant-electron ferromagnet Ni 3 Al and its carbon-intercalated compounds Ni 3 AlC x ( x = 0.01, 0.02, 0.04, 0.05, 0.08, and 0.1) were synthesized and investigated by magnetization measurements between 2 and 300 K with the magnetic field H up to 5 T and 27 Al NMR measurements at H = 7.4847 T. The Curie temperature is suppressed and disappears only by the carbon intercalation with x = 0.02. For the samples with x ≤0.02, the T 4/3 -temperature dependence of M s 2 ( M s : spontaneous magnetization) and χ 0 -1 (χ 0 : initial susceptibility) are newly observed, being consistent with the predication of the self-consistent renormalization theory of spin fluctuations for weak itinerant ferromagnets. The coupling constant between the 27 Al Knight shift and the bulk susceptibility of Ni 3 AlC 0.1 is three times larger than that of Ni 3 Al, suggesting the drastic change of the electronic state by the carbon intercalation.

We report 125 Te and 139 La NMR studies for single crystals of LaTe 3 between 10 and 160 K under an applied field of H = 7.4841 T. We observed the broad 125 Te(1) NMR signals of metallic Te(1) sheets with a superlattice modulation and the sharp 125 Te(2) and 139 La NMR signals of LaTe(2) b i -layers. Temperature dependence of 125 Te(1) nuclear spin–lattice relaxation times of the modulated Te(1) sheets obeys a modified Korringa relation. The results indicate that the electronic state on the Te(1) sheets is a Landau–Fermi liquid on a misfit superlattice or a Tomonaga–Luttinger liquid in a two-dimensional charge-density wave ordering state.

Co nuclear-quadrupole-resonance (NQR) measurements were performed on various bilayered hydrate cobaltate Na x (H 3 O) z CoO 2 · y H 2 O with different values of the superconducting and magnetic-ordering temperatures, T c and T M , respectively. From measurements of the temperature and sample dependence of the NQR frequency, it was revealed that the NQR frequency is changed by the change of the electric field gradient (EFG) along the c axis ν z z rather than the asymmetry of EFG within the a b -plane. In addition, it is considered that the change of ν z z is gaverned mainly by the trigonal distortion of the CoO 2 block layers along the c axis, from the relationships between ν z z and the various physical parameters. We found the tendency that samples with ν z z larger than 4.2 MHz show magnetic ordering, whereas samples with lower ν z z show superconductivity. We measured the nuclear spin–lattice relaxation rate 1/ T 1 in these samples, and found that magnetic fluctuations depend on samples. The higher-ν z...

We report 59Co nuclear quadrupole resonance (NQR) studies of bilayer water intercalated sodium cobalt oxides NaxCoO2.yH2O (BLH) with the superconducting transition temperatures, 2 K < T_c +-7/2 and found a dome shape superconducting phase. The 59Co NQR spectrum of the non-superconducting BLH shows a broadening below T_M without the critical divergence of 1/T_1 and 1/T_2, suggesting an unconventional magnetic ordering. The degree of the enhancement of 1/T_1T at low temperatures increases with the increase of nu_3 though the optimal nu_3~12.30 MHz. In the NaxCoO2.yH2O system, the optimal-T_c superconductivity emerges close to the magnetic instability. T_c is suppressed near the phase boundary at nu_3~12.50 MHz, which is not a conventional magnetic quantum critical point., 4 pages, 5 figures