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Magnetic properties of Mott–Hubbard systems are generally dominated by strong antiferromagnetic interactions produced by the Coulomb repulsion of electrons. Although theoretical possibility of a ferromagnetic ground state has been suggested by Nagaoka and Penn as single-hole doping in a Mott insulator, experimental realization has not been reported more than half century. We report the first experimental possibility of such ferromagnetism in a molecular Mott insulator with an extremely light and homogeneous hole-doping in π-electron layers induced by net polarization of counterions. A series of Ni(dmit)2 anion radical salts with organic cations, where dmit is 1,3-dithiole-2-thione-4,5-dithiolate can form bi-layer structure with polarized cation layers. Heat capacity, magnetization, and ESR measurements substantiated the formation of a bulk ferromagnetic state around 1.0 K with quite soft magnetization versus magnetic field (M–H) characteristics in (Et-4BrT)[Ni(dmit)2]2 where Et-4BrT is ethyl-4-bromothiazolium. The variation of the magnitude of net polarizations by using the difference of counter cations revealed the systematic change of the ground state from antiferromagnetic one to ferromagnetic one. We also report emergence of metallic states through further doping and applying external pressures for this doping induced ferromagnetic state. The realization of ferromagnetic state in Nagaoka–Penn mechanism can paves a way for designing new molecules-based ferromagnets in future.

The $B$-site ordered double perovskites ${\mathrm{Sr}}_{2}\mathrm{Cu}({\mathrm{Te}}_{1\ensuremath{-}x}{\mathrm{W}}_{x}){\mathrm{O}}_{6}$ provide an excellent arena for investigating exotic phases expected for the ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ square-lattice Heisenberg antiferromagnet. Here, combining magnetic susceptibility and specific-heat measurements with electron spin resonance (ESR) and muon spin rotation/relaxation $(\ensuremath{\mu}\mathrm{SR})$ techniques, we explore a spin-liquid-like state in the vicinity of the N\'eel critical end point $(x=0.05--0.1)$. The specific heat and the ESR and muon relaxation rates give evidence for an energy hierarchy of low-energy excitations, reminiscent of randomness-induced singlet states. In addition, the weak transverse $\ensuremath{\mu}\mathrm{SR}$ data show a fraction of frozen magnetic moments in the random-singlet background. The origin of a random-singlet-like state near the phase boundary is discussed in terms of concomitant exchange randomness and local strain generated by the ${\mathrm{W}}^{6+}\text{\ensuremath{-}}\mathrm{for}\text{\ensuremath{-}}{\mathrm{Te}}^{6+}$ substitution.

Magnetization, specific heat, and electron spin resonance (ESR) measurements are carried out to clarify the low-energy excitations for the $S=1/2$ polyhedral clusters ${\mathrm{M}{\mathrm{o}}_{72}{\mathrm{V}}_{30}}$ and ${{\mathrm{W}}_{72}{\mathrm{V}}_{30}}$. The clusters provide unique model systems of a kagom\'e network on a quasisphere. The linear field variation of magnetization at low temperatures indicates that the ground state is singlet for both clusters. The temperature and the magnetic field dependence of specific heat shows a distinct difference between the two clusters with differing structural symmetries. In ${{\mathrm{W}}_{72}{\mathrm{V}}_{30}}$ with ${I}_{\mathrm{h}}$ symmetry, the existence of several tens of low-energy singlet excited states below the lowest triplet excited state is revealed. The specific heat of the slightly distorted ${\mathrm{M}{\mathrm{o}}_{72}{\mathrm{V}}_{30}}$ with ${D}_{5\mathrm{h}}$ symmetry leads to a drastic decrease of the singlet contribution, which is consistent with the partial lifting of the frustration and the decrease of degenerated low-energy states. The singlet excitation existence is confirmed further by the temperature dependence of the ESR spectra. Comprehensive experimental studies have demonstrated unique low-energy excitations of the spherical kagom\'e networks and their sensitivity to the cluster symmetry.

There are few reports on zero-field-cooled (ZFC) magnetization measurements for Fe@FeOx or FeOx particles synthesized by laser ablation in liquids (LAL) of Fe, and the minimum blocking temperature (TB) of 120 K reported so far is still much higher than those of their counterparts synthesized by chemical methods. In this work, the minimum blocking temperature was lowered to 52 K for 4&ndash, 5 nm &alpha, Fe2O3 particles synthesized by femtosecond laser ablation of Fe in acetone. The effective magnetic anisotropy energy density (Keff) is calculated to be 2.7&ndash, 5.4 &times, 105 J/m3, further extending the Keff values for smaller hematite particles synthesized by different methods. Large amorphous-Fe@&alpha, Fe2O3 and amorphous-Fe@C particles of 10&ndash, 100 nm in diameter display a soft magnetic behavior with saturation magnetization (Ms) and coercivities (Hc) values of 72.5 emu/g and 160 Oe at 5 K and 61.9 emu/g and 70 Oe at 300 K, respectively, which mainly stem from the magnetism of amorphous Fe cores. Generally, the nanoparticles obtained by LAL are either amorphous or polycrystalline, seldom in a single-crystalline state. This work also demonstrates the possibility of synthesizing single-crystalline &alpha, Fe2O3 hematite crystals of several nanometers with (104), (113), (116) or (214) crystallographic orientations, which were produced simultaneously with other products including carbon encapsulated amorphous Fe (a-Fe@C) and Fe@FeOx core-shell particles by LAL in one step. Finally, the formation mechanisms for these nanomaterials are proposed and the key factors in series events of LAL are discussed.

There are few reports on zero-field-cooled (ZFC) magnetization measurements for Fe@FeOx or FeOx particles synthesized by laser ablation in liquids (LAL) of Fe, and the minimum blocking temperature (TB) of 120 K reported so far is still much higher than those of their counterparts synthesized by chemical methods. In this work, the minimum blocking temperature was lowered to 52 K for 4–5 nm α-Fe2O3 particles synthesized by femtosecond laser ablation of Fe in acetone. The effective magnetic anisotropy energy density (Keff) is calculated to be 2.7–5.4 × 105 J/m3, further extending the Keff values for smaller hematite particles synthesized by different methods. Large amorphous-Fe@α-Fe2O3 and amorphous-Fe@C particles of 10–100 nm in diameter display a soft magnetic behavior with saturation magnetization (Ms) and coercivities (Hc) values of 72.5 emu/g and 160 Oe at 5 K and 61.9 emu/g and 70 Oe at 300 K, respectively, which mainly stem from the magnetism of amorphous Fe cores. Generally, the nanoparticles obtained by LAL are either amorphous or polycrystalline, seldom in a single-crystalline state. This work also demonstrates the possibility of synthesizing single-crystalline α-Fe2O3 hematite crystals of several nanometers with (104), (113), (116) or (214) crystallographic orientations, which were produced simultaneously with other products including carbon encapsulated amorphous Fe (a-Fe@C) and Fe@FeOx core-shell particles by LAL in one step. Finally, the formation mechanisms for these nanomaterials are proposed and the key factors in series events of LAL are discussed.

We previously reported the importance of induced nuclear transglutaminase (TG) 2 activity, which results in hepatic cell death, in ethanol-induced liver injury. Here, we show that co-incubation of either human hepatic cells or mouse primary hepatocytes derived from wild-type but not TG2−/− mice with pathogenic fungi Candida albicans and C. glabrata, but not baker’s yeast Saccharomyces cerevisiae, induced cell death in host cells by enhancing cellular, particularly nuclear, TG activity. Further pharmacological and genetic approaches demonstrated that this phenomenon was mediated partly by the production of reactive oxygen species (ROS) such as hydroxyl radicals, as detected by a fluorescent probe and electron spin resonance. A ROS scavenger, N-acetyl cysteine, blocked enhanced TG activity primarily in the nuclei and inhibited cell death. In contrast, deletion of C. glabrata nox-1, which encodes a ROS-generating enzyme, resulted in a strain that failed to induce the same phenomena. A similar induction of hepatic ROS and TG activities was observed in C. albicans-infected mice. An antioxidant corn peptide fraction inhibited these phenomena in hepatic cells. These results address the impact of ROS-generating pathogens in inducing nuclear TG2-related liver injuries, which provides novel therapeutic targets for preventing and curing alcoholic liver disease.

The antiferromagnetic insulating ground state of the π–d molecular conductor λ-(BETS)2FeCl4 has been under intense debate for the last decades. One of the difficulties in studying this system comes...

A micro-calorimeter working at ultra-low temperature down to 75 mK and high magnetic field up to 17.5 T has been developed. A typical sample weight is as small as 100 μg. A magnetic phase diagram of magnon Bose-Einstein condensation (BEC) in Ba3Cr2O8 is determined. The scaling index of the phase boundary is very close to that of the isotropic three dimensional BEC at low temperature, in spite of the existence of Dzyaloshinskii-Moriya (DM) interaction which is confirmed in the previous ESR measurement.

Spins in a two-dimensional triangular lattice are geometrically frustrated and cannot form an ordered ground state. Instead, a spin-liquid state is expected, and now thermodynamic measurements suggest that a spin liquid exists down to the lowest temperatures. In two-dimensional triangular lattices, geometric frustration prohibits the formation of ordering even at the lowest temperatures, and therefore a liquid-like ground state is expected. The spin-liquid problem has been one of the central topics of condensed-matter science for more than 30 yr in relation to the resonating-valence-bond model1. One of the characteristic features proposed is the existence of a linear temperature-dependent contribution to the heat capacity, as the degeneracy of the energy states should give rise to gapless excitations. Here, we show thermodynamic evidence for the realization of a spin-liquid ground state through a single-crystal calorimetric study of the dimer-based organic charge-transfer salt κ-(BEDT-TTF)2Cu2(CN)3, with a triangular lattice structure down to 75 mK. In addition, we report an unexpected hump structure in the heat capacity around 6 K, which may indicate a crossover into the quantum spin liquid.

ESR measurements of β-(BDA-TTP)2FeCl4 have been performed to investigate its magnetic properties. At room temperature, the angular dependence of the ESR linewidth shows the typical behavior of a one-dimensional magnetic system. The ESR line shape profiles also support this result. These results suggest that significant π-d interactions exist in the system. The angular dependence of ESR at several temperature ranges will be presented.

The magnetic properties of the ferromagnetic ring-shaped single-molecule magnet (n-BuNH3)12[(CuCl)6 (AsW9O33)2] 6H2O, known as Cu6, have been studied by electron spin resonance (ESR). The ESR spectra show several sharp absorptions, which originates from the multiplet splitting of the high spin ground state S = 3. Meanwhile, the frequency-field plot of the observed ESR shows a gap at zero-field suggesting the existence of an anisotropic exchange interaction in the system. Moreover, forbidden ESR transitions of ΔSz = ±2 have been also observed where the origin comes from the mixing of the spin state by virtue of the transverse field component of the anisotropy.

The detailed topology of the Fermi surface of the quasi-one-dimensional conductor (DMET)2I3 was investigated by the magnetooptical measurements. A pair of planar Fermi surface which has higher corrugations of Fourier components was observed. This result seems to suggest that the metallic state of this salt is stabilized by the higher corrugations of the Fermi surface.

The πd molecular conductor λ‐(BETS)2FeCl4, where BETS is bis(ethylenedithio) tetraselenafulvalene, has attracted considerable interest for the discovery of its field induced superconducting state. A mystery of this system is its antiferromagnetic insulating ground state. The point still under strong debate is whether the d spins in Fe3+ are ordered or not. Here, we review experimental and theoretical studies on the antiferromagnetic insulating phase in λ‐(BETS)2FeCl4 and mention our perspective based on our ESR measurements for λ‐(BETS)2FexGa1−xCl4. Our ESR results indicate that the π‐d interaction in the system is very strong and there is no sign of paramagnetic Fe spins in the antiferromagnetic ground state.

A novel bilayer Mott system, (Et-4BrT)[Ni(dmit)2]2 (Et-4BrT = ethyl-4-bromothiazolium; dmit = 1,3-dithiole-2-thione-4,5-dithiolate), contains two nonequivalent Ni(dmit)2 anion layers, where both layers form Mott insulating states. Supramolecular Br(cation)···S(anion) and S(cation)···S(anion) interactions play a crucial role in constructing the bilayer structure. The ferro- and antiferromagnetic short-range-ordering layers coexist in the crystal, which achieves large negative magnetoresistance (Δρ/ρ0 ≈ -75% at 70 kOe) at 5 K under 1 GPa.

Recently, advanced research into fine filament technology for tape-shaped superconducting-coated conductors composed of REBa2Cu3O7–δ (RE123, RE: rare earth such as Gd or Y, 0 < δ < 1) has been carried out to improve performance in high magnetic fields by reducing the large diamagnetism of the RE123 superconducting layer. The major challenge for high-field NMR/MRI applications is to obtain high tensile stress tolerance above 500 MPa with a high critical current. In this study, a RE123 multi-core superconductor was fabricated via an 'inner split' method using a commercially available RE123 single-core coated conductor, where only the ceramics (RE123 and buffer layers) in wire are electrically separated to multi-filaments without superconducting current flow between the filaments. Experimental results show that wires having 2, 3, 4, or 5 cores have a high critical current (above 95% of the original) and maintain tensile stress tolerance above 650 MPa. The diamagnetism of the five-core wire is reduced ~85% of the original at 7 T. Thus, the wire was optimized via inner split method for high-field use.

We performed combined magnetotransport and cyclotron resonance experiments on two-dimensional electron systems confined in the Mg(x)Zn(1-x)O/ZnO heterostructures over a wide range of carrier densities, from 1.9 to 12 × 10(11) cm(-2) (3.5

A new class of Ni(dmit)(2) anion radical salt (Et-2,5-DBrP)[Ni(dmit)(2)](2) (1) (Et-2,5-DBrP = ethyl-2,5-dibromopyridinium) was developed. Single-crystal X-ray diffraction analysis indicates that this salt contains two crystallographically independent anion layers in the crystal with effective Br···S halogen bonds between the cation and the anion. The crystal and electronic structures, and electrical and magnetic measurements reveal that 1 is a novel bilayer Mott system, in which two different Mott-insulating anion layers coexist in one crystal. Selective halogen substitution of Br with I at the 2-position in the cation affords the isostructural bilayer salt (Et-2I-5BrP)[Ni(dmit)(2)](2) (2) (Et-2I-5BrP = ethyl-2-iodo-5-bromopyridinium), while substitution at the 5-position results in a structural change, yielding the monolayer salt (Et-2Br-5IP)[Ni(dmit)(2)](2) (3) (Et-2Br-5IP = ethyl-2-bromo-5-iodopyridinium). These results indicate that the halogen bond plays an important role to realize the bilayer system, and that the crystal structure is controlled by tuning the strength of the halogen bond. The low temperature magnetic properties of the two isostructural salts 1 and 2 are significantly different, because they are affected by fluctuated spins that do not participate in the formation of short-range antiferromagnetic domains. The bilayer salt generates the fluctuated spins more easily than conventional monolayer salts, and such fluctuated spins are expected to result in unique physical properties.

In Mott insulators, the strong electron-electron Coulomb repulsion prevents metallicity and charge excitations are gapped. In dimensions greater than one, their spins are usually ordered antiferromagnetically at low temperatures. Geometrical frustrations can destroy this long-range order, leading to exotic quantum spin liquid (QSL) states. However, their magnetic ground states have been a long-standing mystery. Here we show that a QSL state in the organic Mott insulator EtMe$_3$Sb[Pd(dmit)$_2$]$_2$ with two-dimensional triangular lattice has Pauli-paramagnetic-like low-energy excitations, which are a hallmark of itinerant fermions. Our torque magnetometry down to low temperatures (30 mK) up to high fields (32 T) reveal distinct residual paramagnetic susceptibility comparable to that in a half-filled two-dimensional metal. This demonstrates that the system is in a magnetically gapless ground state, a critical state with infinite magnetic correlation length. Moreover, our results are robust against deuteration, pointing toward the emergence of an extended `quantum critical phase', in which low-energy spin excitations behave as in paramagnetic metals with Fermi surface, despite the frozen charge degree of freedom., Comment: 7 pages, 3 figures. Published in Nature communication

The quasi-two-dimensional molecular conductor $\ensuremath{\lambda}$-(BETS)${}_{2}$FeCl${}_{4}$, where BETS is bis(ethylenedithio)tetraselenafulvalene, shows a superconductivity in the high magnetic field environment. This is due to the compensation effect between the external field and the internal field created by the Fe${}^{3+}$ magnetic moment. Here, we report the simultaneous transport and electron spin resonance (ESR) measurements in the field-induced superconducting state down to 1.65 K. We find that the field-induced superconductivity is partially destroyed by ESR transitions, namely, by dynamical spin reversals of Fe${}^{3+}$. Moreover, it is found from our ESR results that the field-induced superconducting state is inhomogeneous, coexisting with the residual paramagnetic metal state.

The magnetism of the polyoxometalate cluster {${\text{Mo}}_{75}{\text{V}}_{20}$}, containing a sawtooth ring of 10 corner-sharing triangles located on the equator of the barrel-shaped molecule, has remained debatable since it is masked by contributions from impurities as well as temperature-independent paramagnetism. In this paper, we demonstrate the usefulness of electron spin resonance (ESR) measurements, since the temperature dependence of the ESR intensity can discriminate between impurity and molecular contributions. We determine the exchange parameters and therefore also the low-lying spectrum of {${\text{Mo}}_{75}{\text{V}}_{20}$}, especially the low-lying singlet states which so far have been probed solely by specific-heat measurements.

A fundamental understanding of the conduction mechanisms in single-wall carbon nanotube (SWCNT) networks is crucial for their use in thin-film transistors and conducting films. However, the uncontrollable mixture state of metallic and semiconducting SWCNTs has always been an obstacle in this regard. In the present study, we revealed that the conduction mechanisms in nanotube networks formed by high-purity metallic and semiconducting SWCNTs are completely different. Quantum transport was observed in macroscopic networks of pure metallic SWCNTs. However, for semiconducting SWCNT networks, Coulomb-gap-type conduction was observed, due to Coulomb interactions between localized electrons. Crossovers among a weakly localized state and strongly localized states with and without Coulomb interactions were observed for transport electrons by varying the relative content of metallic and semiconducting SWCNTs. It was found that hopping barriers, which always exist in normal SWCNT networks and are serious obstacles to achieving high conductivity, were not present in pure metallic SWCNT networks.

We report on theoretical and experimental results concerning the low-temperature specific heat of the frustrated spin-tube material [(CuCl(2)tachH)(3)Cl]Cl-2 (tach denotes 1,3,5-triaminocyclohexane). This substance turns out to be an unusually perfect spin-tube system which allows to study the physics of quasione- dimensional antiferromagnetic structures in rather general terms. An analysis of the specific-heat data demonstrates that at low enough temperatures the system exhibits a Tomonaga-Luttinger liquid behavior corresponding to an effective spin-3/2 antiferromagnetic Heisenberg chain with short-range exchange interactions. On the other hand, around 2 K the composite spin structure of the chain is revealed through a Schottky-type peak in the specific heat. We argue that the dominating contribution to the peak originates from gapped magnon-type excitations related to the internal degrees of freedom of the rung spins.

The intrinsic magnetotransport effect of the single-walled carbon nanotube (SWNT) has been observed by the cavity perturbation technique, which is a noncontact method for evaluating transport properties. The inverse Q factor of the cavity resonator, which corresponds to the resistance of the sample, shows a linear increase as a function of the magnetic field. The angular and tube diameter dependence of oriented SWNT thin films, and measurements using sorted SWNTs reveal that the observed positive magnetoresistance is due to the Aharonov-Bohm effect of metallic nanotubes.

By using bulk magnetization, electron spin resonance (ESR), heat capacity, and neutron scattering techniques, we characterize the thermodynamic and quantum phase diagrams of ${\mathrm{Ba}}_{3}{\mathrm{Cr}}_{2}{\mathrm{O}}_{8}$. Our ESR measurements indicate that the low field paramagnetic ground state is a mixed state of the singlet and the ${S}_{z}=0$ triplet for $H\ensuremath{\perp}c$. This suggests the presence of an intradimer Dzyaloshinsky-Moriya (DM) interaction with a DM vector perpendicular to the $c$ axis.

Our periodic orbit resonance (POR) results on quasi-two-dimensional (q2D), highly anisotropic q2D and quasi-one-dimensional (q1D) organic conductors are reviewed together with our rotational cavity magneto-optical measurement system. Higher order POR up to seventh order has been observed in the q2D system (BEDT-TTF)2Br(DIA), and the experimental conditions to observe POR and the cyclotron resonance (CR) are discussed. Highly anisotropic q2D Fermi surface (FS) in β''-(BEDT-TTF)(TCNQ), which was considered to have q1D FS previously, is proposed by our POR measurements, and the possible interpretations of other experimental results of β''-(BEDT-TTF)(TCNQ) are discussed assuming the highly anisotropic q2D FS. Finally, detailed q1D FS of (DMET)2I3, obtained from our POR results, is discussed in connection with the typical q1D system (TMTSF)2ClO4.

Electron spin resonance reveals the spin behavior of conduction ($\ensuremath{\pi}$) and localized ($d$) electrons in $\ensuremath{\beta}\mathrm{\text{\ensuremath{-}}}(\mathrm{BDA}\mathrm{\text{\ensuremath{-}}}\mathrm{TTP}{)}_{2}M{\mathrm{Cl}}_{4}$ ($M=\mathrm{Fe}$, Ga). Both the ${\mathrm{Ga}}^{3+}(S=0)$ and ${\mathrm{Fe}}^{3+}(S=5/2)$ compounds exhibit a metal-insulator transition at 113 K with the simultaneous formation of a spin-singlet ground state in the $\ensuremath{\pi}$ electron system of the donor molecules. The behavior is consistent with charge ordering in $\ensuremath{\beta}\mathrm{\text{\ensuremath{-}}}(\mathrm{BDA}\mathrm{\text{\ensuremath{-}}}\mathrm{TTP}{)}_{2}M{\mathrm{Cl}}_{4}$ at the metal-insulator transition. At 5 K, the ${\mathrm{Fe}}^{3+}$ compound orders antiferromagnetically, even though the $\ensuremath{\pi}$ electrons, which normally would facilitate magnetic exchange, are localized nonmagnetic singlets.

Two unique materials based on Mn4 single-molecule magnet (SMM) clusters (ST=9) and integer or non-integer average valent platinum maleonitriledithiolate (mnt2-) complexes, [{MnII2MnIII2(hmp)6(MeCN)2}{Pt(mnt)2}2][Pt(mnt)2]2.2MeCN (1) and [{MnII2MnIII2(hmp)6(MeCN)2}{Pt(mnt)2}4][Pt(mnt)2]2 (2), were synthesized by the material diffusion method and electrochemical oxidation, respectively (hmp-=2-hydroxymethylpyridinate). 1 and 2 are comprised of four and six [Pt(mnt)2]n- units, respectively, in addition to a common MnII2MnIII2 double-cuboidal unit, [MnII2MnIII2(hmp)6(MeCN)2]4+ (hereinafter [Mn4]4+). Among the [Pt(mnt)2]n- units, two units in 1 and four units in 2 are coordinated with the [Mn4]4+ unit, forming a 1D chain of {-[Mn4]-[Pt(mnt)2]2-} for 1 and a discrete subunit of {[Pt(mnt)2]2-[Mn4]-[Pt(mnt)2]2} for 2. The other two [Pt(mnt)2]n- units, occupying void space of the packing, form a stacking column with the coordinating [Pt(mnt)2]n- units, finally constructing hybrid frames of aggregates consisting of [Mn4]4+ units and [Pt(mnt)2]n- units. Electronic conductivity measurements revealed that 1 is an insulator and 2 is a semiconductor with sigma=0.22 S.cm(-1) at room temperature and an activation energy of 136 meV. Detailed magnetic measurements proved that the [Mn4]4+ units in 1 and 2 behave as SMMs with an ST=9 ground state at low temperatures. There is no significant interaction between [Mn4]4+ units and [Pt(mnt)2]n- units, but interactions between localized spins of [Pt(mnt)2]n- were detected even in 2 at low temperatures where the conductivity is electronically insulated. 2 is the first example of a hybridized material exhibiting SMM behavior and electronic conductivity.

Magnetooptical measurements of a quasi-two-dimensional (q2D) organic conductor (BEDT-TTF)2Br(DIA) (DIA=diiodoacetylene) were performed using a cavity perturbation technique with a millimeter vector network analyzer (MVNA). Harmonic resonances were observed periodically as a function of the inverse field up to the 7th order. This is the first observation of higher-order harmonics up to the 7th order in an organic conductor. The observed resonance is assigned as a periodic orbit resonance (POR) which arises from a q2D elliptic Fermi surface (FS). The obtained effective mass (4.7me) is consistent with Shubnikov-de Haas measurements. Temperature dependence of the spectra observed in two different sample configurations will be presented., 7 pages, 5 figures, to be published in J. Phys. Soc. Jpn Vol. 71 No.4

A high-field magnetization process for the triangular spin prism Na 17 [Mn 6 (H 2 O) 2 (AsW 9 O 34 ) 2 (AsW 6 O 26 )]·38H 2 O, which consists of six Mn 2+ ions ( S =5/2), has been investigated. The magnetization at low temperature shows a 1/3 plateau around 5.5 T. It is examined by theoretical calculations using exact diagonalization. The experimental results can be reproduced, but only in a restricted parameter range. It implies that the plateau originates from a delicate balance of exchange couplings. We propose that the plateau is stabilized by some external perturbations, such as thermal/quantum fluctuations.

A rotational resonant cavity equipped with a millimeter vector network analyzer (MVNA) and a 14 T solenoid type superconducting magnet has been developed. The available frequency range is about 50–100 GHz. The temperature can decrease to 1.5 K. The cavity can rotate within the precision of one degree. As an example of the application of the new resonant cavity, we have performed detailed magnetooptical measurements of an organic conductor to estimate the Fermi surface topology. The Fermi surface of the quasi-one-dimensional conductor (DMET)2I3 is discussed.