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Anomalous successive structural transitions in layered 1T-CrSe2 with an unusual Cr4+ valency were investigated by synchrotron X-ray diffraction. 1T-CrSe2 exhibits dramatic structural changes in in- ...

An $A$-type antiferromagnet, ${\mathrm{NaNiO}}_{2}$, was examined by means of positive muon spin rotation and relaxation (${\ensuremath{\mu}}^{+}\mathrm{SR}$) measurements and first-principles calculations based on a density functional theory (DFT). Below ${T}_{\mathrm{N}}=20$ K, a clear muon spin precession signal was observed in the ${\ensuremath{\mu}}^{+}\mathrm{SR}$ time spectrum recorded under zero field, due to the formation of a static internal magnetic field. The microscopic origin of such an internal field was computed as a sum of dipolar and hyperfine contact fields at the site (0.624, 0, 0.854), where both the muon site and the local spin density at such a site were predicted with DFT calculations. While the computed values were consistent with experimentally obtained ones, in both the antiferromagnetic and the paramagnetic states, the contribution of the hyperfine contact field was shown to be insignificant even below ${T}_{\mathrm{N}}$. Finally, measurements at higher temperatures signified thermally activated Na-ion diffusion with ${E}_{\mathrm{a}}=50(20)$ meV and ${D}_{\mathrm{Na}}(300\phantom{\rule{0.16em}{0ex}}\mathrm{K})=8.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{2}$/s, commonly observed in layered-type compounds.

The physical properties of novel cluster-based triangular lattice antiferromagnets Na3 A2 (MoO4 )2 Mo3 O8 (A=In, Sc), synthesized through a topochemical Na-intercalation to nonmagnetic Na2 A2 (MoO4 )2 Mo3 O8 , are reported. The S=1/2 [Mo3 ]11+ clusters form a regular triangular lattice, which gives the magnetic system a strong geometrical spin frustration effect. Despite the strong antiferromagnetic couplings among [Mo3 ]11+ clusters, they show no long-range magnetic orderings down to 0.5 K with the finite residual magnetic entropy. The ground states of Na3 A2 (MoO4 )2 Mo3 O8 have been characterized as a quantum spin liquid, owing to the strong spin frustration of cluster spins on the triangular lattice.

We investigated the magnetic properties of the ilmenite-type manganates $\mathrm{MgMn}{\mathrm{O}}_{3}$ and $\mathrm{ZnMn}{\mathrm{O}}_{3}$, both of which are composed of a honeycomb lattice of magnetic $\mathrm{M}{\mathrm{n}}^{4+}$ ions. Both compounds show antiferromagnetic order with weak ferromagnetic moments. In particular, $\mathrm{MgMn}{\mathrm{O}}_{3}$ exhibits a magnetization ``reversal'' behavior which can be described by the $N$-type ferrimagnetism in the N\'eel's classification. The relationship between the magnetic properties and the crystal and magnetic structures probed by the neutron diffraction experiments indicates that the two honeycomb lattice magnets have different ${J}_{1}\ensuremath{-}{J}_{2}$ parameter sets, placing them in the distinct regions in the phase diagram; both nearest neighbor (NN) and next nearest neighbor (NNN) exchange interactions are antiferromagnetic in $\mathrm{MgMn}{\mathrm{O}}_{3}$, while NN and NNN interactions become ferromagnetic and antiferromagnet, respectively, in $\mathrm{ZnMn}{\mathrm{O}}_{3}$.

We synthesized a kagome fluoride ${\mathrm{Cs}}_{2}{\mathrm{LiTi}}_{3}{\mathrm{F}}_{12}$ with $S=1/2$ spins, and studied magnetic properties of the compound. The temperature dependence of the magnetic susceptibility indicates that it has dominant antiferromagnetic interactions and that it has no magnetic order down to 2 K. We found two magnetization plateaus in its magnetization process approximately at 1/3 and 0.8 ${\ensuremath{\mu}}_{\mathrm{B}}$ per Ti. The monoclinic crystal structure gives four inequivalent nearest-neighbor exchange interactions. Our density functional theory calculations suggest that three of them are antiferromagnetic and one of them is weakly ferromagnetic, resulting in a magnetic system composed of antiferromagnetically coupled linear chains and $\mathrm{\ensuremath{\Delta}}$ chains. This explains the observed suppression of magnetic order. Numerical diagonalization gives a magnetization curve in good agreement with the experimental results.

We have investigated the structural and magnetic properties of $S=3/2\phantom{\rule{4pt}{0ex}}{\mathrm{Cr}}^{3+}$ Heisenberg-like kagome lattice antiferromagnets ${\mathrm{Cs}}_{2}{\mathrm{K}}_{}{\mathrm{Cr}}_{3}{\mathrm{F}}_{12}$ and ${\mathrm{Cs}}_{2}{\mathrm{Na}}_{}{\mathrm{Cr}}_{3}{\mathrm{F}}_{12}$ using single crystals. Each compound has a slightly distorted kagome lattice, although the space groups differ for the two compounds. The magnetic data suggest that each compound exhibits the formation of antiferromagnetic ordering with in-plane-spin canting approximately below 6 K. The in-plane coplanar structures are clearly different from disordered ground states of the isostructural ${\mathrm{Ti}}^{3+}$ compounds and out-of-plane coplanar structures of the ${\mathrm{V}}^{3+}$ compounds, which is mainly caused by the differences in the strength of quantum fluctuation and the strength of magnetic anisotropy for these three spin systems. In contrast, as well as the ${\mathrm{Ti}}^{3+}$ and ${\mathrm{V}}^{3+}$ compounds, the magnetization curves show 1/3-magnetization-plateaulike anomalies.

We have successfully synthesized the novel antiferromagnets with Ir$^{4+}$ honeycomb lattice ZnIrO$_3$ and MgIrO$_3$ and investigated their magnetic and thermodynamic properties. The two iridates are isomorphic but exhibit qualitatively different magnetic properties. ZnIrO$_3$ shows antiferromagnetic ordering below 46.6 K, whereas MgIrO$_3$ displays weak ferromagnetic behavior below 31.8 K owing to formation of a canted antiferromagnetic ordering. The measurement of magnetic susceptibility with using an oriented powder sample revealed the presence of an XY-like magnetic anisotropy and a tilting magnetic structure which is possibly stabilized by the Kitaev interaction. Moreover, magnetization curves of MgIrO3 and ZnIrO3 up to 60 T show different behaviors, demonstrating that each magnetic ground state is different with each other. We discuss the difference in the ground state between MgIrO$_3$ and ZnIrO$_3$ from the viewpoint a magnetic model consisting of the Kitaev and Dzyaloshinskii-Moriya interactions with the spin frustration effect on the honeycomb lattice.

In order to elucidate the dependence of the magnetic ground state on the Ca content (x) in Sr1-xCaxCo2P2 (0 ≤x ≤1, ThCr2Si2-type structure), we have performed muon spin rotation− and relaxation (μ+SR) experiments on Sr1-xCax Co2P2 powder samples mainly in a zero applied field. The end member compound, SrCo2P2, is found to be paramagnetic down to 19 mK. As x increases, such a paramagnetic ground state is observed down to 1.8K until x = 0.45. Then, as x increases further, a short-range antiferromagnetic (AF) ordered phase appears at low temperatures for 0.48 ≤ x ≤ 0.75, and finally, a long-range AF ordered phase is stabilized for x > 0.75. The internal magnetic field of the other end member compound, CaCo2P2, is well consistent with that of the A-type AF order state, which was proposed from neutron scattering experiments. The phase diagram determined with μ+SR is different from that proposed by macroscopic measurements. For an isostructural compound, LaCo2P2, static magnetic order is found to be formed below

We have investigated crystal structure and magnetic properties of three $S=1\phantom{\rule{4pt}{0ex}}{\mathrm{V}}^{3+}$ Ising-like anisotropic kagome lattice antiferromagnets, ${\mathrm{Cs}}_{2}\mathrm{K}{\mathrm{V}}_{3}{\mathrm{F}}_{12},{\mathrm{Cs}}_{2}\mathrm{Na}{\mathrm{V}}_{3}{\mathrm{F}}_{12}$, and ${\mathrm{Rb}}_{2}\mathrm{Na}{\mathrm{V}}_{3}{\mathrm{F}}_{12}$, using single crystals. Each compound crystallizes in a monoclinic system and has a slightly distorted kagome lattice. Although the magnetic properties are similar, the details depend on the magnitude of magnetic anisotropy. The magnetization and magnetic susceptibility are highly anisotropic owing to anisotropic $g$ factors and Ising-like single ion anisotropy originating from partially unquenched orbital moments of ${\mathrm{V}}^{3+}$, and the easy axis of Ising-like anisotropy is perpendicular to the kagome plane. In contrast to disordered ground states in the isostructural ${\mathrm{Ti}}^{3+}$ $(S=1/2)$ compounds, the ${\mathrm{V}}^{3+}$ $(S=1)$ compounds exhibit antiferromagnetic ordering with distorted ${120}^{\ensuremath{\circ}}$ structure or other nearly coplanar magnetic structure whose basal spin plane includes the easy axis, which is mainly due to large magnetic anisotropy and decrease of quantum fluctuation. Moreover, when magnetic fields are applied perpendicular to the kagome plane, magnetization curves of them show distinct 1/3 and 2/3 magnetization plateaus, which are stabilized by Ising-like single ion anisotropy. In particular, the 2/3 magnetization plateaus are notable magnetic phenomena in kagome lattice antiferromagnets and are due to the combination of spin frustration, Ising-like single ion anisotropy, and the small monoclinic distortion of kagome lattices.

We took $^{31}\text{P}$ NMR measurements of mainly paramagnetic phase ${\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{Co}}_{2}{\mathrm{P}}_{2}$ ($0\ensuremath{\le}x\ensuremath{\le}0.5$) to reveal the itinerant-electron metamagnetic transition, and of its magnetically ordered phase ($0.7\ensuremath{\le}x\ensuremath{\le}1$), and characterized their spin fluctuations by estimating the spin fluctuation parameter ${T}_{0}$ corresponding to the width of the spin fluctuation in the spectrum in frequency space. ${\mathrm{SrCo}}_{2}{\mathrm{P}}_{2}$ has a quasi-two-dimensional uncollapsed tetragonal (ucT) cell without interlayer P-P bonds, whereas ${\mathrm{CaCo}}_{2}{\mathrm{P}}_{2}$ has a three-dimensional collapsed tetragonal (cT) cell with P-P bonds. The $ab$-in-plane component of ${T}_{0}$ is much larger than the out-of-plane component in ${\mathrm{SrCo}}_{2}{\mathrm{P}}_{2}$. As $x$ increases from 0 to 0.5, the in-plane component of ${T}_{0}$ decreases proportionally with the metamagnetic transition field. In the antiferromagnetic cT phase ($0.7\ensuremath{\le}x\ensuremath{\le}1$), ${T}_{0}$ is constant and spin fluctuations show an isotropic character in contrast to their behavior in the paramagnetic ucT phase ($0\ensuremath{\le}x\ensuremath{\le}0.5$). These results indicate that the in-plane spin fluctuations due to the quasi-two-dimensional crystal structure play a significant role in the metamagnetic transition of this system.

We report on the dynamics of the spin-1/2 quasi-one-dimensional frustrated magnet LiCuVO$\mathrm{_4}$ measured by nuclear spin relaxation in high magnetic fields 10--34 T, in which the ground state has spin-density-wave order. The spin fluctuations in the paramagnetic phase exhibit striking anisotropy with respect to the magnetic field. The transverse excitation spectrum probed by $^{51}$V nuclei has an excitation gap, which increases with field. On the other hand, the gapless longitudinal fluctuations sensed by $^7$Li nuclei grow with lowering temperature, but tend to be suppressed with increasing field. Such anisotropic spin dynamics and its field dependence agree with the theoretical predictions and are ascribed to the formation of bound magnon pairs, a remarkable consequence of the frustration between ferromagnetic nearest neighbor and antiferromagnetic next-nearest-neighbor interactions., Comment: 7 pages, 6 figures

We have investigated the crystal structure and magnetic properties of three kagome lattice antiferromagnets, ${\mathrm{Rb}}_{2}\mathrm{Na}{\mathrm{Ti}}_{3}{\mathrm{F}}_{12}, {\mathrm{Cs}}_{2}\mathrm{Na}{\mathrm{Ti}}_{3}{\mathrm{F}}_{12}$, and ${\mathrm{Cs}}_{2}\mathrm{K}{\mathrm{Ti}}_{3}{\mathrm{F}}_{12}$, using single crystals. These compounds represent a $S=1/2$ kagome system consisting of magnetic ${\mathrm{Ti}}^{3+}$ ions, which is expected to have negligibly small Dzyaloshinsky-Moriya interaction. The structural analyses revealed that each of the three compounds has a slightly distorted kagome lattice. The distortion of the kagome lattice becomes small as the ionic radii of constituent alkali metals increase. All three compounds have nearly the same Weiss temperature of $\ensuremath{-}45$ K, and the ground states are disordered and strongly depend on the distortion. The ground states of ${\mathrm{Rb}}_{2}\mathrm{Na}{\mathrm{Ti}}_{3}{\mathrm{F}}_{12}, {\mathrm{Cs}}_{2}\mathrm{Na}{\mathrm{Ti}}_{3}{\mathrm{F}}_{12}$, and ${\mathrm{Cs}}_{2}\mathrm{K}{\mathrm{Ti}}_{3}{\mathrm{F}}_{12}$ are found to be a two-component state including approximately 1/3 nearly free spins, a gapless disordered state, and a gapped disordered state, respectively. Our experimental results suggest that the ground state of the ideal $S=1/2$ Heisenberg kagome lattice antiferromagnet is gapped. In addition, the magnetization curves of ${\mathrm{Cs}}_{2}\mathrm{Na}{\mathrm{Ti}}_{3}{\mathrm{F}}_{12}$ and ${\mathrm{Cs}}_{2}\mathrm{K}{\mathrm{Ti}}_{3}{\mathrm{F}}_{12}$ show anomalies at approximately 1/3 of the full magnetic moment of ${\mathrm{Ti}}^{3+}$, which are a notable observation of signs of the theoretically proposed 1/3 magnetization plateau in $S=1/2$ kagome antiferromagnets.

Physical properties of new S = 3/2 triangular-lattice compounds LiCrSe2, LiCrTe2, and NaCrTe2 have been investigated by X-ray diffraction and magnetic measurements. These compounds crystallize in the ordered NiAs-type structure, where alkali metal ions and Cr atoms stack alternately. Despite their isomorphic structures, magnetic properties of these three compounds are different; NaCrTe2 has an A-type spin structure with ferromagnetic layers, LiCrTe2 is likely to exhibit a helical spin structure, and LiCrSe2 shows a first-order-like phase transition from the paramagnetic trigonal phase to the antiferromagnetic monoclinic phase. In these compounds and the other chromium chalcogenides with a triangular lattice, we found a general relationship between the Curie-Weiss temperature and magnetic structures. This relation indicates that the competition between the antiferromagnetic direct d-d exchange interaction and the ferromagnetic superexchange interaction plays an important role in determining the ground state of chromium chalcogenides.

The magnetic nature of a metallic two-dimensional triangular compound, ${\mathrm{CrSe}}_{2}$, has been investigated by muon spin rotation and relaxation ($\ensuremath{\mu}^{+}\mathrm{SR}$) measurements using both powder and single crystal samples. It is found that ${\mathrm{CrSe}}_{2}$ enters into a static antiferromagnetic (AF) ordered state below 157 K ($={T}_{\mathrm{N}}$). Furthermore, the AF state is slightly changed below around 20 K ($={T}_{\mathrm{N}2}$). Based on the analysis of the internal magnetic fields at the muon sites predicted with DFT calculations, collinear AF and helical ${120}^{\ensuremath{\circ}}$ AF are clearly eliminated for the ground state of ${\mathrm{CrSe}}_{2}$. The most probable one is an incommensurate spin density wave order.

We have investigated structural, electrical, and magnetic properties of single crystals of modified pyrochlore fluorides ${\mathrm{Rb}}_{}{\mathrm{V}}_{2}{\mathrm{F}}_{6}$ and ${\mathrm{Cs}}_{}{\mathrm{V}}_{2}{\mathrm{F}}_{6}$, which have mixed-valent V atoms. At room temperature, they have orthorhombic structures. With increasing temperature, each of them exhibits two structural transitions, and electrical resistivity rapidly decreases accompanied with one of these structural changes. The changes of unit cell volume and electrical resistivity at these transition temperatures indicate that the structural instability and the charge ordering cause structural transitions of ${\mathrm{Rb}}_{}{\mathrm{V}}_{2}{\mathrm{F}}_{6}$ and ${\mathrm{Cs}}_{}{\mathrm{V}}_{2}{\mathrm{F}}_{6}$, respectively. At low temperatures, ${\mathrm{Cs}}_{}{\mathrm{V}}_{2}{\mathrm{F}}_{6}$ shows antiferromagnetic ordering at $5\phantom{\rule{4pt}{0ex}}\mathrm{K}$, and ${\mathrm{Rb}}_{}{\mathrm{V}}_{2}{\mathrm{F}}_{6}$ shows two-step magnetic transitions.

In order to elucidate the details of successive magnetic transitions in the rare earth cobalt arsenic oxides ( RE CoAsO), we have measured muon-spin rotation and relaxation( μ + SR) spectra of powder samples with RE = La, Ce, Pr, Nd, Sm, and Gd. Together with the result of magnetization measurements, it was found that all the compounds enter into abulk static ferromagnetic ordered phase below around 70 K(= T C ). Furthermore, additional transitions into a static antiferromagnetic ordered phase were found for the RE = Nd, Sm, and Gd compounds; namely T N1 = 15 K and T N2 = 7 K for Nd, T N1 = 41.5 K and T N2 = 17.5 K for Sm, and T N = 3K for Gd.

A topotactic ion-exchange reaction of a layered perovskite RbSr2Ta3O10 with NiCl2 yielded a novel two-dimensional nickel-oxyhalide (NiCl)Sr2Ta3O10, the first S = 1 compound among related series of metal-oxyhalides. The room temperature structure is isostructural with (CuCl)Ca2Nb3O10 adopting the space group P4/mmm. We found a possible structural transition at 230 K that does not lead to drastic changes in magnetic character such as nickel clustering. Despite a large Weiss temperature of θ = −125 K, magnetic long-range order is significantly suppressed down to TN1 ≈ 50 K because of two-dimensionality and strong frustration. The magnetically ordered state below TN1 has a partial volume fraction coexisting with a paramagnetic component, followed by complete long-range ordering below TN2 = 20 K. The reaction process and requirement will also be discussed.

The S = 1/2 triangular-lattice Heisenberg antiferromagnet with distortion is investigated by the numerical-diagonalization method. The examined distortion type is \(\sqrt{3} \times \sqrt{3} \). We study the case when the distortion connects the undistorted triangular lattice and the dice lattice. For the intermediate phase reported previously in this system, we obtain results of the boundaries of the intermediate phase for a larger system than those in the previous report and examine the system size dependence of the boundaries in detail. We also report the specific heat of this system, which shows a marked peak structure related to the appearance of the intermediate state.

The spin-1/2 triangular-lattice Heisenberg antiferromagnet with a √3 × √3 -type distortion is studied by the numerical-diagonalization method. We examine this model between the two cases, one is the undistorted triangular lattice and the other is the model on the honeycomb lattice with isolated spins. When the distortion is controlled, we find a nontrivial region where the ground states shows spontaneous magnetization; the magnitude increases gradually as the distortion is larger and is smaller than one third of the saturated magnetization., 28th International Conference on Low Temperature Physics (LT28) 9–16 August 2017, Gothenburg, Sweden.

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.

Spin transition has attracted the interest of researchers in various fields since the early 1930s, with thousands of examples now recognized, including those in minerals and biomolecules. However, so far the metal centres in which it has been found to occur are almost always octahedral six-coordinate 3d4 to 3d7 metals, such as Fe(II). A five-coordinate centre is only rarely seen. Here we report that under pressure SrFe(II)O2, which features a four-fold square-planar coordination, exhibits a transition from high spin (S = 2) to intermediate spin (S = 1). This is accompanied by a transition from an antiferromagnetic insulating state to a ferromagnetic so-called half-metallic state: only half of the spin-down (dxz, dyz) states are filled. These results highlight the square-planar coordinated iron oxides as a new class of magnetic and electric materials., 四本の手をもつ金属原子の磁性の変換に成功 －磁気記録、スイッチ素子の革新につながるか－. 京都大学プレスリリース. 2009-07-21.

The influence of composition on the structural ordering and magnetism in the V x Nb 1+ y S 2 system has been investigated by X-ray diffraction and magnetic measurements. Stoichiometric V 1/3 NbS 2 did not exhibit the structural ordering of vanadium between the NbS 2 layers. In the ordered structure, the vanadium composition deviated from the ideal value of x = 1 3 to both higher and lower values, while the niobium composition was in the range of 0.05⩽ y ⩽0.18. Excess niobium, y >0, is thought to play an essential role in the structural ordering in this system. For samples with excess niobium and ordered structures, a magnetic transition was observed at 20–50 K, depending on the composition. The spontaneous magnetization of 3–5×10 −3 μ B /V atom is thought to be intrinsic to this system. The magnetization curves consisted of a constant and a proportional parts of the magnetic field, which correspond to the spontaneous magnetization and high-field susceptibility, respectively. The magnetization curves and the temperature dependencies of the high-field susceptibility were quite similar to those of the canted antiferromagnetic NiS 2 . A correlation between the structural and magnetic ordering is suggested.

Two new tetranuclear complexes of macrocyclic oxamide [Cd(CuL)3](NO3)2·2.5H2O 1, [Mn(CuL)3(OH)2](ClO4)2·Mn(H2O)6·4.5H2O 2 (L = 1,4,8,11-tatraazacyclotradecanne-2,3-dione) have been synthesized, structurally characterized and preliminary investigated by magnetic studies. The structures of the title complexes consist of a tetranuclear units MCu3 (M = Cd, Mn), the packing diagram shows two-dimensional and three-dimensional system through intermolecular weak interactions. The temperature-dependent magnetic susceptibilities of complex 2 were analyzed by an approximate treatment leading to J = −33 cm−1, gCu = 2.10, gMn = 1.95 indicating antiferromagnetic exchange between Cu(II) and Mn(II) ions.

A transition metal-radical heterospin complex [Ni(salox) 2 (IM4Py) 2 ] ( 1 ) (salox = salicylaldoxime, IM4Py = 2-(4′-pyridinyl)-4,4,5,5-tetramethylimidazoline-l-oxyl) ( 1 ) has been synthesized based on the substitution reaction of Ni(salox) 2 (py) 2 and IM4Py. Compound 1 exhibits a chain structure created by the intermolecular hydrogen bonds. Magnetic measurements show intermolecular antiferromagnetic interactions in 1 .

We report on the electronic ground state of a layered perovskite vanadium oxide ${\mathrm{Sr}}_{2}{\mathrm{VO}}_{4}$ studied by the combined use of synchrotron radiation x-ray diffraction (SR-XRD) and muon spin rotation/relaxation $(\ensuremath{\mu}\mathrm{SR})$ techniques, where $\ensuremath{\mu}\mathrm{SR}$ measurements were extended down to 30 mK. We found an intermediate orthorhombic phase between ${T}_{\mathrm{c}2}\ensuremath{\sim}130$ K and ${T}_{\mathrm{c}1}\ensuremath{\sim}100$ K, whereas a tetragonal phase appears for $Tg{T}_{\mathrm{c}2}$ and $Tl{T}_{\mathrm{c}1}$. The absence of long-range magnetic order was confirmed by $\ensuremath{\mu}\mathrm{SR}$ at the reentrant tetragonal phase below ${T}_{\mathrm{c}1}$, where the relative enhancement in the $c$-axis length versus that of the $a$-axis length was observed. However, no clear indication of the lowering of the tetragonal lattice symmetry with superlattice modulation, which is expected in the orbital order state with superstructure of ${d}_{yz}$ and ${d}_{zx}$ orbitals, was observed by SR-XRD below ${T}_{\mathrm{c}1}$. Instead, it was inferred from $\ensuremath{\mu}\mathrm{SR}$ that a magnetic state developed below ${T}_{\mathrm{c}0}\ensuremath{\sim}10$ K, which was characterized by the highly inhomogeneous and fluctuating local magnetic fields down to 30 mK. We argue that the anomalous magnetic ground state below ${T}_{\mathrm{c}0}$ originates from the coexistence of ferromagnetic and antiferromagnetic correlations.

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.

A novel copper(II)-radical complex [Cu(NITmPy)(PDA)(H2O)] · (H2O) (1) (NITmPy = 2-(3′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, H2PDA = 2,6-pyridinedicarboxylic acid) has been synthesized and structurally characterized by X-ray diffraction methods. It crystallizes in the triclinic space group P 1 ¯ . The Cu(II) ion exists in a distorted square pyramid environment. The molecules of [Cu(NITmPy)(PDA)(H2O)] · (H2O) are connected as a two-dimensional structure by the intermolecular hydrogen bonds. Magnetic measurements show intramolecular ferromagnetic interactions between NITmPy and Cu(II) ion and intermolecular antiferromagnetic interactions in 1.

High-field magnetization measurements have been performed up to 56 T for a two-dimensional S = 1/2 frustrated square-lattice antiferromagnet (CuCl)LaNb 2 O 7 , a recently discovered spin gap system (Δ/ k B = 26.7 K). It is found that the spin gap closes at a surprisingly low field H c1 = 10.3 T compared with that expected from the zero-field spin gap (Δ/ g µ B = 18.4 T). For H > H c1 , the magnetization exhibits a linear increase without any trace of anomalies such as fractional plateaus until it saturates at H c2 = 30.1 T. This means that the gapless phase, where the field-induced magnetic ordering is expected to occur at low temperatures, is stable over a wide field region. These results suggest strong correlations of triplet excitations in the layer and the proximity of the spin-liquid phase to the magnetically ordered phase.

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 .

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.

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...

High-field ESR technique has been applied to the novel frustrated spin chain system KCu5V3O13, to reveal the peculiar ground state proposed by the previous results of the magnetic susceptibility and the magnetization measurements. We successfully observed the antiferromagnetic resonance with the easy axis type anisotropy below 7 K . In addition, small shifts of the resonance field probably due to the re-arrangements of spin configuration in the ordered phase were also observed at about 4 K in the detailed temperature dependence measurements. This result confirmed the observation of double peaks at 3.9 and 7 K in the specific heat measurements performed in advance to the high-field ESR measurements. We will discuss about the ground state of KCu5V3O13 based on these results together with those obtained in the KMgCu4V3O13, where no antiferromagnetic resonance was observed.

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

The magnetic properties of Ca 3 FeRhO 6 , which is isostructural with the rhombohedral K 4 CdCl 6 -type structure, were investigated by magnetic susceptibility and high-field magnetization measurements using field-oriented samples and 57 Fe Mossbauer spectroscopy using a powder sample. We observed anisotropy in the magnetic susceptibility below 12 K and the spin–flop transition in the magnetization curve at 4.2 K. The 57 Fe Mossbauer spectra show that the Fe ions occupy the trigonal prism site in the trivalent state with the high-spin configuration. It has been confirmed from our investigations that Ca 3 FeRhO 6 orders below 12 K antiferromagnetically with the strong magnetic anisotropy along the c -axis. The quantitative analysis suggests that the Rh ions occupy the trigonal prism site partially in place of the Fe ions.

We report magnetic properties of CuSb 2− x Ta x O 6 with tri-rutile type structure. Solubility limit was determined to be x =1.0 by the solid-state reaction and X-ray diffraction measurements. The value of J , the magnetic interaction obtained by Bonner–Fisher fitting, was found to decrease gradually with Ta content x . The value of T N also decreases with x and seems to be zero at x =0.6. As a result of our structural analysis, this fact shows the crossover from one-dimensional to two-dimensional magnetic system with a local distortion caused by Ta substitution. Although the ground state of the compound with x >0.6 is not clear, it can be considered that the long-range antiferromagnetic order disappears and that the quantum critical regime such as a spin-singlet state is realized in this system.

The magnetic susceptibility and the 63,65 Cu nuclear quadrupole resonance have been measured in the quasi-one-dimensional cuprate Ca 0.85 CuO 2 which contains edge-sharing CuO 2 chains separated by Ca layers. The behaviors of the magnetic susceptibility and the 63 Cu nuclear spin–lattice relaxation rate are well explained by assuming the coexistence of an antiferromagnetic ordering and spin gap states which can be realized in the hole doped 1D Cu–O chain.

51 V nuclear magnetic resonance and relaxation are reported for the Hollandite Bi 1.77 V 8 O 16 system. Bi x V 8 O 16 having the Hollandite structure with 1.6 x x T 1 of 51 V NMR to investigate the magnetic and electric properties of Bi 1.77 V 8 O 16 , which will provide information on the electronic states below and above the MIT temperature T MIT in this system. Above T MIT , the temperature dependence of 1/ T 1 T obeys a modified Korringa relaxation with a large correlation factor K ( α )=3.2, implying that the antiferromagnetic spin fluctuations are dominant in the metallic regime of the present system.

The magnetic susceptibility, the magnetization process, the specific heat and the 51 V NMR have been investigated on the powder sample of Bi 4 Cu 3 V 2 O 14 , which has a characteristic chain structure. The magnetic susceptibility has a broad maximum around 20.5 K. The magnetization curve bends upward at 6.7 T and around 15 T, and increases linearly below 6.7 T, between 7 T and 11 T, and above 20 T. From the NMR measurement, it has been crucially proved that the ground state of this compound is an antiferromagnetically ordered state. The Neel temperature T N is determined to be 6 K from the specific heat measurement. The hyperfine field at the vanadium site at 4.2 K is obtained to be 2.12 kOe. The isotropic and anisotropic hyperfine coupling constants are determined as A hf iso =20.4 kOe/µ B and A hf aniso =4.97 kOe/µ B in the paramagnetic region. It has been, furthermore, suggested that the physical properties of this compound are due to the novel spin chain.

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 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

A powder sample of KCu 5 V 3 O 13 was synthesized and is expected to represent a novel frustrated spin chain system based on its characteristic crystal structure. The magnetic susceptibility and the high-field magnetization process were investigated in order to elucidate the ground state of this spin chain system. From the results, the ground state of this compound appears to be an antiferromagnetically ordered state. The transition temperature was determined to be T N =7.8 K. However, there are some anomalous behaviors evident in both the susceptibility and the magnetization curves: the Curie constant and the Weiss temperature change markedly around 75 K, the gradient of the magnetization curve becomes small after a spin-flop transition, and the number of the ordered spins is only 1/5 of all the copper spins. Assuming that the other spins vanish by forming a spin-singlet state, the energy gap was estimated to be 44.3 K from the magnetization curve. Thus, the classical renormalized ordered state may coexi...

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.

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 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.

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.

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.