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In order to study the effect of muonic-Li on the µ− SR spectrum for Li battery materials, the transverse field (TF) µ− SR spectra have been measured for natural Li metal and 6Li metal samples in the temperature range between 5 and 300 K. Here, TF denotes the magnetic field perpendicular to the initial µ− spin polarization. For both samples, the TF-µ− SR spectrum showed a clear oscillation without relaxation down to the lowest temperature measured: i.e., about 5 K. This clearly excludes the scenario that the muonic-Li starts to diffuse at a certain temperature between 5 and 300 K. Although the mechanism on such a zero TF relaxation rate is not fully understood, we could ignore the contribution from the muonic Li on the asymmetry spectrum for the Li-ion battery materials at temperatures above 5 K.

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 lower critical field of type-II organic layered superconductor l-(BETS)2GaCl4 has been estimated by magnetic measurements. The demagnetization factor of a needle-like sample shape has been taken into account for the measurements by applying the external field, parallel and perpendicular to the conducting plane. The lower critical field for the field parallel to the conducting plane is 5.5(2) G, in contrast with the previous studies. This allows us to discuss the anisotropy of lower critical field Hc1 in a quasi-two-dimensional organic layered superconductor l-(BETS)2GaCl4.

We have investigated the low-temperature magnetism of sodium superoxide (NaO2), in which spin, orbital, and lattice degrees of freedom are closely entangled. The magnetic susceptibility shows anomalies at T1 = 220 K and T2 = 190 K, which correspond well to the structural phase transition temperatures, and a sudden decrease below T3 = 34 K. At 4.2 K, the magnetization shows a clear stepwise anomaly around 30 T with a large hysteresis. In addition, the muon spin relaxation experiments indicate no magnetic phase transition down to T = 0.3 K. The inelastic neutron scattering spectrum exhibits magnetic excitation with a finite energy gap. These results confirm that the ground state of NaO2 is a spin-singlet state. To understand this ground state in NaO2, we performed Raman scattering experiments. All the Raman-active libration modes expected for the marcasite phase below T2 are observed. Furthermore, we find that several new peaks appear below T3. This directly evidences the low crystal symmetry, namely, the presence of the phase transition at T3.We conclude that the singlet ground state of NaO2 is due to the spin-Peierls instability.

The lower critical field of type-II organic layered superconductor λ-(BETS)2GaCl4 has been estimated by magnetic measurement. In this study, the demagnetization factor of a needle-like sample shape has been taken into account for the measurements by applying external field, parallel and perpendicular to the conducting plane. The lower critical field for the field perpendicular to the conducting plane is 8(1) G, convincing the previous study. This estimation allows us to predict the ideal external field that should be applied for London penetration depth measurement by using muon-spin rotation (SR) spectroscopy.

Polycrystalline rubidium superoxide (RbO2) has been synthesized by using solution method followed by the reaction process under the cooling condition of-40 °C. X-ray Powder Diffraction (XRD) spectra showed that RbO2 was successfully synthesized by this method. The magnetic susceptibility and pulsed muon spin relaxation (μSR) measurements were carried out in order to study the magnetic properties of RbO2.

The internal magnetic field in a sodium battery compound, i.e., the paramagnet ${\mathrm{Na}}_{0.7}{\mathrm{CoO}}_{2}$, was investigated with negative muon spin rotation and relaxation (${\ensuremath{\mu}}^{\ensuremath{-}}\mathrm{SR}$), and the result was compared with the results previously obtained with ${\ensuremath{\mu}}^{+}\mathrm{SR}$. The majority of implanted ${\ensuremath{\mu}}^{\ensuremath{-}}$ is captured on an oxygen nucleus, while ${\ensuremath{\mu}}^{+}$ locates an interstitial site. Therefore, a ${\ensuremath{\mu}}^{\ifmmode\pm\else\textpm\fi{}}\mathrm{SR}$ work provides information on the internal magnetic field, which is formed by nuclear magnetic moments of $^{23}\mathrm{Na}$ and $^{59}\mathrm{Co}$, from the two different viewpoints. Besides a slight decrease in the field distribution width ($\mathrm{\ensuremath{\Delta}}$) around 300 K, the nuclear magnetic field detected with ${\ensuremath{\mu}}^{\ensuremath{-}}\mathrm{SR}$ was found to be almost static and temperature independent up to 400 K, even though Na ions are known to start to diffuse above 290 K based on ${\ensuremath{\mu}}^{+}\mathrm{SR}$, Na-NMR, neutron scattering, and electrochemical measurements. Such a discrepancy is caused by the fact that the Na contribution to $\mathrm{\ensuremath{\Delta}}$ is only about 3% at the O site whereas it is about 13% at the interstitial site, where the ${\ensuremath{\mu}}^{+}$ is presumably located.

Magnetodielectric properties of the tetragonal magnetic insulator Ba(TiO)Cu4(PO4)4 consisting of asymmetric Cu4O12 square cupolas have been investigated in a magnetic field along the [001] axis (B[001]), where a metamagnetic transition occurs at Bc||[001] ~ 12 T and 1.4 K. Clear anomalies associated with the transition to the high-field phase are observed in dielectric constants both along the [100] (e[100]) and [001] (e[001]) axes. It is found that the B dependence of e[001] and e[100] across Bc||[001] is anisotropic: e[001] decreases while e[100] increases. The origin of this anisotropic magnetodielectric response is discussed.

We have performed X-band electron spin resonance (ESR) measurements on a single crystal of the metallic chiral helimagnet ${\mathrm{CrNb}}_{3}{\mathrm{S}}_{6}$ from 3.5 to 180 K and for the external magnetic fields ${H}_{\mathrm{ext}}$, up to 4 kOe, perpendicular to the $c$ axis (the helical axis of ${\mathrm{CrNb}}_{3}{\mathrm{S}}_{6}$). This field-crystalline configuration is expected to provide the chiral soliton lattice (CSL) state in this system. The main resonance line can be fit with a Dysonian function above ${T}_{\mathrm{c}}=127\phantom{\rule{0.0pt}{0ex}}\phantom{\rule{4pt}{0ex}}\mathrm{K}$, but additional features in the spectra were observed below 105 K. Specifically, spiked anomalies superposed on the main signals were observed for magnetic fields between ${H}_{\mathrm{c}1}$ and ${H}_{\mathrm{c}2}$ that are the appearing and disappearing fields of the spiked anomalies, respectively. The resulting magnetic field vs temperature phase diagram possesses three regions, which are interpreted as different dynamical responses in the CSL phase. In addition, the values of ${H}_{\mathrm{c}2}$ are close to those reported by the ${d}^{2}M/d{H}^{2}$ curve [Tsuruta et al., Phys. Rev. B 93, 104402 (2016)]. Furthermore, the field range between ${H}_{\mathrm{c}1}$ and ${H}_{\mathrm{c}2}$, where the spiked anomalies exist, depends on the field direction and shifts to higher fields when turning to the $c$ axis, thereby providing additional evidence that these spiked anomalies must be related to the chiral soliton dynamics.

Potassium metal was loaded into K-form zeolite low-silica $\mathrm{X}$ $(\mathrm{LSX})$ under the loading pressure $P$ up to 1.5 GPa. A ferromagnetism is observed at $P\ensuremath{\approx}$ 0.9 GPa below 13 K. The loading density of K atom $n$ is estimated to be $\ensuremath{\approx}15$ per cage at the ferromagnetic loading pressure, and the pressure-derivative loading density $dn/dP$ has a remarkable peak $\ensuremath{\approx}11\phantom{\rule{4pt}{0ex}}{\mathrm{GPa}}^{\ensuremath{-}1}$ at $P\ensuremath{\approx}0.95$ GPa. The density of states at the Fermi energy is estimated to be $\ensuremath{\approx}46$ states/eV per cage from the value of $dn/dP$ on a simple model. The observed ferromagnetism is discussed in terms of the Stoner condition and the theory of the revised Rhodes-Wohlfarth plot.

A new layered manganese(II) phosphite, |NH4|4[Mn4(PO3H)6] (JIS-10), has been synthesised via the ionothermal method by using 1-pentyl-3-methylimidazolium bromide ([Pmim]Br) as the solvent. JIS-10 is the first manganese phosphite with a Mn/P ratio of 2/3, whose layered framework is built by the alternate connection of Mn2O9 dimers and PO3H pseudo-tetrahedra. JIS-10 represents an antiferromagnetic dimer system with S = 5/2 for each Mn2+ ion.

The ground state of alkali metals when the particle size decreases from bulk to nanometric atomic clusters is inevitably accompanied by quantum effects that can suppress their pristine metallic state. We demonstrate that the metallic nature of rubidium clusters confined and arrayed in the framework of insulating low-silica X zeolite is preserved. The $^{87}$Rb NMR spin-lattice relaxation assigned to rubidium clusters in supercages shows a Korringa behavior from 190~K down to 10~K, which is compatible with a macroscopic observation of low electrical resistivity. The density of states at the Fermi level is found to be enhanced compared to the analogous sodium case, consistent with a Holstein-Hubbard model of alkali-loaded zeolites., Comment: Extended version showing new data, 4+epsilon pages, 4 figures

We report on the experimental results of magnetic susceptibility, specific heat, electron spin resonance (ESR), and high-field magnetization measurements on a polycrystalline sample of the spin-$1/2$ distorted honeycomb-lattice antiferromagnet Cu$_2$(pymca)$_3$(ClO$_4$). Magnetic susceptibility shows a broad peak at about 25~K, which is typical of a low dimensional antiferromagnet, and no long range magnetic order is observed down to 0.6~K in the specific heat measurements. Magnetization curve up to 70~T at 1.4~K shows triple stepwise jumps. Assuming three different exchange bonds $J_{\rm A}$, $J_{\rm B}$ and $J_{\rm C}$ from the structure, the calculated magnetization curve reproduces the observed one when $J_{\rm A}/k_{\rm B} = 43.7~{\rm K}$, $J_{\rm B}/J_{\rm A} = 1$ and $J_{\rm C}/J_{\rm A} = 0.2$ except the magnetization near 70~T, where the observed magnetization indicates another step while the calculated magnetization becomes saturated. The relationship between magnetization plateaus and exchange bonds is discussed based on the numerical calculations., Comment: 5 pages, 5 figures

Alkali superoxide CsO2 is one of candidates for the spin-1/2 one-dimensional (1D) antiferromagnet, which may be sequentially caused by an ordering of the pi-orbital of O2- molecule below TS ~ 70 K. Here, we report on the magnetism in powder CsO2 and high-magnetic field magnetization measurements in pulsed-magnetic fields of up to 60 T. We obtained the low temperature phase diagram around the antiferromagnetic ordering temperature TN = 9.6 K under the magnetic field. At 1.3 K, remarkable up-turn curvature in the magnetization around a saturation field of ~ 60 T is found, which corresponds to the spin-1/2. We will compare it with the theoretical calculation., Comment: 11 pages, 3 figures

The evolution of the electronic properties of guest Na and Rb atoms in a disordered deformable lattice is investigated for a series of guest-atom densities $n$. The quasi-two-dimensional host ${M}_{7.8\ensuremath{-}\ensuremath{\delta}}{\mathrm{Al}}_{7.8}{\mathrm{Si}}_{8.2}{\mathrm{O}}_{32.0}$ ($M$=Na, Rb), known as zeolite P, is used. The Na system is a stubborn bipolaronic insulator to the maximum $n$ of 1.03. In contrast, the Rb system exhibits a crossover from a bipolaronic insulator to a conducting phase analogous to a disordered metal at $n$ = 0.89. A critical region undergoing polaronic melting appears in the vicinity of the crossover on the insulating side, evidenced by a reduction in the small bipolaron absorption band and a drop in the activation energy. Transition to the conducting phase coincides with the appearance of a midinfrared band and an increase in the charge-carrier decay length, suggesting the polaronic and extended nature of the carriers. These findings constitute rare examples of electron-lattice coupling opening (or closing) a mobility gap and scaling the continuity (or discontinuity) of a conducting transition in the face of disorder.

Crystal structures of sodium clusters incorporated in LSX zeolite [Na12Al12Si12O48 (Z = 8)] with FAU-type topology are analyzed by powder X-ray diffraction. The two different Na-loaded samples, Na9.4/Na12-LSX and Na16.7/Na12-LSX, show insulating and metallic states, respectively. The insulating state is changed to the metallic state upon increasing the loading density of Na atoms. The two samples have the space group Fd3 attributed to cubic symmetry and lattice constants of a = 2.49646(3) nm for Na9.4/Na12-LSX and a = 2.495060(11) nm for Na16.7/Na12-LSX. In both samples, three cation sites at the centers of two types of 6-ring of the sod-cage and the centers of the d6r prism are fully occupied by Na ions. In addition, a large number of Na cations forming Na clusters are distributed in the cavity (supercage), and Na distribution inside the cavity is disorderly, which is represented by several independent sites with low site occupancy. Electron-density distribution analysis clearly reveals the covalent bon...

X-ray powder diffraction (XRPD), magnetic susceptibility and muon-spin relaxation (μSR) measurements were carried out to investigate lattice symmetries and magnetic properties of one of alkali-meta...

Zeolite LSX (low-silica X) crystals have an aluminosilicate framework with regular supercages and β-cages. They are arrayed in a double diamond structure. The loading density of guest K atoms per supercage (or β cage), n, can be controlled from 0 to ≈ 9. At n 6. These properties are explained by the polaron effect including the electron correlation. Ferrimagnetic properties are observed at n ≈ 9. A remarkable increase in the resistivity is observed at very low temperatures at n ≈ 9, and is discussed in terms of the hypothesis of a Kondo insulator.

Alkali metal nanoclusters can be stabilized in the regular cages of zeolite crystals by the loading of guest alkali metals. Cages are connected by the sharing of windows of the framework, and arrayed in simple cubic, diamond and body centered cubic structures in zeolites A, X and sodalite, respectively. The s-electrons have the localized nature of nanoclusters with magnetic moments, and have mutual interactions through the windows of cages. They show exotic magnetism depending on the structure type of zeolites, the kind of alkali metals and the average loading density of alkali atoms per cage. In zeolite A, potassium clusters are formed in α-cages that have an inside diameter of 11 A. They exhibit ferromagnetic properties explained by the canted antiferromagnetism of the Mott insulator, where the 1p-like degenerate orbitals of clusters play an essential role in the magnetic properties. Na-K alloy clusters generated at supercages and β-cages of low-silica X (LSX) zeolite exhibit Neel’s N-type ferrimagnetism at specific loading densities of alkali metals. Alkali metal clusters in sodalite show the ideal Heisenberg antiferromagnetism of the Mott insulator.

We prepared Rb-rich K-Rb alloy nanoclusters arrayed in the regular nanospace of aluminosilicate sodalite which has a bcc arrangement of cages. The average chemical formula of the cluster is (K1.5Rb2.5)3+, where one unpaired s-electron is shared by four alkali cations and is confined in a cage. The magnetic susceptibility and the electron spin resonance clearly show an antiferromagnetic phase transition at a Neel temperature TN of approximately 90–100 K. The observed TN is higher than that in K43+ (TN = 72 K) and (K3Rb)3+ clusters (TN = 80 K) in sodalites. This result indicates a systematic enhancement of the antiferromagnetic exchange coupling between the adjacent nanoclusters by substituting Rb atoms for K ones. The size and the spatial distribution of the s-electron wave function in the nanocluster play a key role in the exchange coupling.

27 Al NMR property of rubidium-loaded potassium-type sodalite, which has antiferromagnetic transition temperature T N of 80 K, is reported. Similar to the case of potassium-loaded one, monotonous narrow spectrum is seen above T N and broadened one is observed below T N . Separately shifted component, which is seen in the case of sodium-loaded one, is not observed as the potassium-loaded one. When two Gaussian functions are used for fitting, widths of each Gaussian component fairly scale to each other. The ratio between two Gaussian widths takes close value to the case of potassium loading below 65 K and shows difference above 65 K. This difference comes from the raising of T N by replacement of K to Rb.

Electrical resistivity was measured for Na-doped low-silica X (LSX) zeolite at various Na-loading densities. Many s-electrons are introduced into the regular array of zeolite nanocages by the loading of guest Na atoms. The average Na-loading density per unite cage, n , was changed from 0 to ≈ 12 . Nonmagnetic and insulating properties are observed for n ≲ 11 . A drastic decrease in the resistivity is observed at n ≈ 12 , indicating that the insulating phase is changed to metallic one by the addition of less than one Na-atom per unite cage. At the same time, a remarkable increase in paramagnetic susceptibility is observed at room temperature. Insulating states are explained by spin-singlet clusters which are assigned to the self-trapped s-electron pairs (small bipolarons) due to the strong electron–phonon interaction against the Coulomb repulsive interaction between two s-electrons. Pairs of s-electrons occupy successively the quantum states of clusters in zeolite cages with increasing the Na-loading density. The metallic phase transition is explained by the formation of large polarons which are mobile over many cages through the zeolite windows. The increase in the paramagnetic susceptibility is explained by the thermal excitation of small polarons expected in the adiabatic potential.

A new layered manganese(II) phosphite, |NH4|4[Mn4(PO3H)6] (JIS-10), has been synthesised via the ionothermal method by using 1-pentyl-3-methylimidazolium bromide ([Pmim]Br) as the solvent. JIS-10 is the first manganese phosphite with a Mn/P ratio of 2/3, whose layered framework is built by the alternate connection of Mn2O9 dimers and PO3H pseudo-tetrahedra. JIS-10 represents an antiferromagnetic dimer system with S = 5/2 for each Mn2+ ion.

We report a systematic nuclear magnetic resonance investigation of the 23Na spin-lattice relaxation rate, 1/T1, in sodium loaded low-silica X (LSX) zeolite, Nan/Na12-LSX, for various loading levels of sodium atoms n across the metal-to-insulator crossover. For high loading levels of n ≥ 14.2, 1/T1T shows nearly temperature-independent behaviour between 10 K and 25 K consistent with the Korringa relaxation mechanism and the metallic ground state. As the loading levels decrease below n ≤ 11.6, the extracted density of states (DOS) at the Fermi level sharply decreases, although a residual DOS at Fermi level is still observed even in the samples that lack the metallic Drude-peak in the optical reflectance. The observed crossover is a result of a complex loading-level dependence of electric potential felt by the electrons confined to zeolite cages, where the electronic correlations and disorder both play an important role.

In this article, we have developed pressure loading technique to extend the loading density of guest alkali metals in nanoporous crystals of zeolites. Zeolite crystals have solid framework and open regular nanospace. In the nanocages of zeolite crystals, s-electrons provided by the guest alkali metals occupy quantum electronic states of clusters successively. Under the pressure by the use of the pressure medium of alkali metals, we have observed significant change in the magnetic properties, indicating that the pressure loading increases loading densities which are closely related to the s-electron occupation at the quantum states of clusters.

We have carried out electron spin resonance (ESR) measurements on powder samples of sodalite loaded with Na at several frequencies between 9.7 and 35 GHz and at temperatures between 1.5 and 60 K. The ESR absorption spectrum below a Neel temperature TN turns into an asymmetric spectrum with a long tail at low fields from a symmetric one above TN. The line shape of the spectra below TN is analyzed by a powder pattern simulation of the antiferromagnetic resonance spectra with easy-plane anisotropy. The calculated line shape reproduces the experimental one considerably well by assuming a Gaussian distribution of the zero-field energy gap. We have evaluated a small anisotropy field of about 2×10−4 T by using the exchange coupling constant calculated from the Weiss and the Neel temperatures. This result indicates that the sodalite loaded with Na is quite an ideal Heisenberg antiferromagnet as expected from the s-electron character of Na clusters and the cubic arrangement of nano-spaces in the sodalite.

Na concentration (x) dependence of ferrimagnetic properties is investigated for Na–K alloy clusters incorporated in low-silica X (LSX) zeolite. In the LSX zeolite, β-cages of inner diameter ≈7 A are arranged in a diamond structure, and supercages of inner diameter ≈13 A are formed among them. The used LSX zeolite contains xNa+ and (12−x)K+ cations per β-cage or supercage. Guest nK atoms are loaded into the zeolite, namely the loading density is given by n per β-cage. The samples at x=4 have been reported to show Neel’s N-type ferrimagnetism in the specific region of n. This ferrimagnetism is explained by the model of antiferromagnetic coupling between two non-equivalent magnetic sublattices of clusters, the ones in β-cages and the others in supercages. In the present study, the value of x is changed from 4 to 0. Ferrimagnetic properties are found to show strong x-dependence. A systematic increase in loading densities of ferrimagnetic region is clearly observed with decreasing x. A remarkable change in temperature dependence of spontaneous magnetization is observed depending on x. Na+ cations are known to be mainly distributed in β-cages. Hence, the decrease in Na concentration is proposed to change the electronic potential depth for clusters in β-cage, which leads to important differences in the interaction between electrons localized in β-cages and those in supercages.

Optical and magnetic properties are investigated for low-silica X (LSX) zeolite loaded with Na metals at various loading densities. In LSX, β-cages with the inside diameter of ∼7 A are arrayed in a diamond structure and the supercages with that of ∼13 A are formed among them. When the average number of guest Na atoms per β cage, n, is smaller than ∼2, optical reflectance shows a peak at ∼2.5 eV. This corresponds to the 1s–1p transition of the cluster formed in β cage. At n>2, this peak disappears and several strong peaks are seen at 1–3 eV. The oscillator strength increases with n. They can be attributed to surface-plasmon-like excitations of the Na clusters formed in supercages. At n≤10, clear absorption tails with energy gaps are observed at near IR region indicating insulating states. However, when n is increased up to ∼12, a clear Drude reflection suddenly appears in the IR region, indicating that an insulator-to-metal transition abruptly occurs. This dramatic change of the electronic state may be caused by the successive connection between adjacent clusters in supercages due to some special arrangement of Na+ ions as well as the delocalized wave function of electrons at high Na-loading density.

27Al NMR property of potassium-loaded sodalite, which shows antiferromagnetic transition around 70 K, is reported. Monotonic narrow spectrum above 70 K is broadened below 70 K. The broadened spectrum is analyzed with an assumption that the broadening is given by dipolar field from magnetic moment in the cage of sodalite. Two Gaussian functions are used for fitting. Widths of each component proportionally scale each other. The ratio between the Gaussian widths of each component of the narrower and the broader components is 15±3.

We performed μ SR experiments on rubidium clusters arrayed in porous crystals of zeolite A. These clusters are known to show spontaneous magnetization of ferromagnetism at higher loading densities of Rb atoms in a previous study. The development of the internal field is observed below ≃ 4 K in the temperature dependence of zero-field μ SR spectra in the sample n = 5.8 , where n is the average loading density of Rb atoms per unit cage. The Curie temperature of this sample is estimated to be ≃ 5 K from the Arrott plot analysis. The amplitude of the relaxation is large enough to indicate the magnetic ordering in the major volume of sample. The internal field is confirmed to be almost static in the longitudinal-field μ SR spectra below ≃ 4 K . Difference of the ferromagnetic properties between K and Rb clusters is also discussed from the viewpoint of μ SR study.

Potassium clusters arrayed in zeolite A are known to show ferromagnetic properties at low temperatures. A remarkable decrease in the initial asymmetry was observed previously below the Curie temperature in zero-field μ SR by using pulsed muons. In the present work by using dc muons, we clearly observed the fast decay component which was assigned to the decrease in the initial asymmetry in the previous pulsed muon experiment. The relaxation rate amounts to ≃ 20 μ s - 1 which corresponds to ≃ 200 Oe in the random static field. This value cannot be explained by the ordinary dipole field, but by the Fermi-contact interaction with electrons in K clusters. The fast decay is easily quenched by applying a weak longitudinal field of ≃ 10 Oe . The low field decoupling of the fast decay component can be explained by the magnetization by the spin-canting mechanism of antiferromagnet under the assumption that some muons stop near the oxygen in 8-membered ring of zeolite framework.

Potassium nanoclusters in aluminosilicate zeolite A shows ferromagnetic properties, although bulk metal of K is nonmagnetic. K clusters are prepared by adsorbing guest K atoms into the supercages (α cages) of dehydrated zeolite A, where supercages with the inside diameter of ∼ 11 A are arrayed in a simple cubic structure. By the loading of guest K atoms, s-electrons are provided for clusters, and successively occupy 1s- and 1p-like quantum states of cluster. The average number of guest K atoms in a cluster, n, is widely controlled up to 7.2. This material shows ferromagnetism at n> 2a t low temperatures, where s-electrons in the 1p state of clusters are responsible for the ferromagnetism. We have found a fine step at n = 2 in magnetization and g value. The g values of ferromagnetic samples with 2

Colour patterns of animals' bodies are usually produced by the spatial distribution of pigments with different colours. However, some animals use the spatial variation of colour-producing microstructures. We have studied one distinctive example of such structurally produced colour patterns, the wing of the Madagascan sunset moth, to clarify the physical rules that underlie the colour variation. It is known that the iridescent wing scale of the sunset moth has the alternate air–cuticle multilayer structure that causes optical interference. The microscopic and optical investigations of various parts of the wing have confirmed that the thickness of the cuticle layers within the scale largely varies to produce the colour pattern. However, it varies in very different ways between the dorsal and ventral sides of the hind wing; the thickness gradually varies on the dorsal side from scale to scale, while the abrupt changes are found on the ventral side to form distinctive borders between differently coloured areas. It is also revealed that an unusual coloration mechanism is involved in the green part of the ventral hind wing: the colour is caused by higher order optical interference of the highly non-ideal multilayer structure. The physical mechanism of the colour pattern formation is briefly discussed with the several mathematical models proposed so far.

Fluorescence from copper phthalocyanine thin films was first observed using tunneling electrons from a scanning tunneling microscope on the Au substrate. The plasmon enhancement effect enables the detection of the fluorescence emission even though the intrinsic fluorescence from a copper phthalocyanine molecule is extremely weak. Moreover, this emission appeared under an energy-forbidden condition, where the fluorescence at the energy of ∼1.7 eV could be observed with bias voltages lower than 1.7 V. As the threshold bias voltage of this emission is ∼1.1 eV, this emission can be explained by the up-conversion transfer resulting from the plasmon-enhanced triplet–triplet annihilation of molecules.

Anomalous temperature dependence of T 2 for 27 Al NMR in dehydrated zeolite A is found. T 2 of the satellite transition shows a minimum around 75 K and a rapid decrease below 140 K, in spite that T 2 of the central transition changes gradually. Since T 1 shows monotonous dependence on temperature for both transitions below 140 K, the anomaly of T 2 cannot be caused by the fluctuation of the local magnetic field. Some lattice dynamics which reveal coherence only among the satellite transitions, such as an alternation of the electrical field gradient, may be an origin of those behaviors.

We have studied orbital dynamics in the spin liquid candidate $\mathrm{B}{\mathrm{a}}_{3}\mathrm{CuS}{\mathrm{b}}_{2}{\mathrm{O}}_{9}$ using multifrequency electron-spin resonance. We prepared two high-quality single crystals. The crystal with a slight copper deficiency shows a structural phase transition at around 200 K due to the cooperative Jahn-Teller effect, accompanied with orbital ordering. In contrast, the crystal with almost perfect stoichiometry shows no orbital ordering down to the lowest temperature of 1.5 K. Dramatic change in the $g$ factor anisotropy as a function of frequency and temperature demonstrates orbital quantum fluctuations at a nearly constant time scale of $\ensuremath{\sim}100\phantom{\rule{0.16em}{0ex}}\mathrm{ps}$ below 20 K, evidencing the emergence of an orbital liquid state in this quantum spin liquid compound.

Synchrotron-radiation-based M\"ossbauer absorption spectroscopy of $^{40}\mathrm{K}$ nuclei was performed. We investigated potassium nanoclusters arrayed in a porous crystal of sodalite. The nanoclusters exhibit antiferromagnetic (AFM) ordering below $\ensuremath{\simeq}72$ K. The energy-domain $^{40}\mathrm{K}$ M\"ossbauer spectra were successfully obtained in the temperature range of 8--140 K. Precise analysis of the spectra indicates the appearance of a hyperfine magnetic field at low temperatures. The hyperfine field was evaluated to be $9.2\ifmmode\pm\else\textpm\fi{}3.0$ T at 8 K. This result signifies the spontaneous polarization of s-electron spins in three-dimensionally arrayed potassium nanoclusters in AFM-ordered states.

Mordenite (structure type MOR) is one of nano-porous crystals of aluminosilicate zeolites. The framework of mordenite has one-dimensional channels along the c-axis. Cations, such as Na, are distributed at the side pockets of channels. We measured polarized far infrared absorption spectra of Na-type mordenite single crystals with the size of less than ∼100 μm. The measurements were performed by the microspectroscopy station of BL43IR at SPring-8. The polarization directions are set for parallel and perpendicular to the c-axis. The polarization dependence is observed clearly in the spectra. Absorption peaks are observed at 140 and 320 cm−1 for parallel polarization and at 170 and 280 cm−1 for perpendicular polarization. They are assigned to the anisotropic motion of Na cations and framework. The spectra are compared with the ordinary absorption spectra of the pellet forms of Na-, Rb- and H-type mordenite powders.

Potassium clusters are stabilized in the cages of low silica X zeolite, where the cages with the inside diameter of ∼13 A are arrayed in a diamond structure. The average number of potassium atoms per cage, n, is changed from ∼6.3 to the saturated value of ∼8.8 by controlling the guest potassium loading density. The temperature dependence of magnetization shows the typical behavior of the N-type ferrimagnetism at n∼6.8 and n∼8.3. The zero field μSR spectra show significant increase in the relaxation rate below the Curie temperature, 5 K, in the sample with n∼6.8. The time dependence of asymmetry shows almost full amplitude of decrease, indicating that the internal field below the magnetic phase transition arises in the almost full volume of the sample. The longitudinal field μSR spectra at 1.7 K show the typical decoupling behavior of a static internal field. A model of ferrimagnetism is proposed based on the structure of the zeolite, where a magnetic sublattice of itinerant electron ferromagnetism is assumed.

A significant decrease in the initial asymmetry of zero-field μSR spectra is observed in dehydrated (nonloaded) zeolite X measured by using pulsed positive-muon beam. This result indicates an effective muonium (Mu) formation in the zeolite crystal. The Mu formation rate is estimated to be ∼40% of the implanted muons. From the analysis of the longitudinal-field decoupling behavior, the hyperfine field of the Mu is estimated to be 1530±100 Oe. This value is quite close to that for Mu in vacuum (∼1580 Oe), indicating that the electron in Mu scarcely hybridizes with the electronic states of zeolite framework. We also observe the significant suppression of Mu formation by the loading of guest potassium atoms into zeolite X. The interaction between the electron in Mu and electrons in potassium cluster in the zeolite cage may play an important role for the suppression of Mu formation.