Search

We have investigated the current-voltage (

We have conducted precise magnetization measurements down to 0.5 K with a miniature 3He cryostat and a closed-cycle 3He gas handling system (GHS) for a superconducting quantum interference device magnetometer. The GHS contains two sorption pumps filled with granular charcoals. We pressurize 3He gas up to ambient pressure for the liquification at 3 K and then pump the vapor for cooling. The lowest sample temperature is ∼0.5 K and it can persist for 34 h. We demonstrate the performance of the system by observing the Meissner effect of aluminum below the superconducting transition temperature ∼1 K. We also measured the magnetization curve of the heavy-fermion superconductor CeCoIn5 resulting in successful observation of the lower critical field at 0.5 K.

The study of transition metal clusters exhibiting fast electron hopping or delocalization remains challenging, because intermetallic communications mediated through bridging ligands are normally weak. Herein, we report the synthesis of a nanosized complex, [Fe(Tp)(CN)3]8[Fe(H2O)(DMSO)]6 (abbreviated as [Fe14], Tp−, hydrotris(pyrazolyl)borate; DMSO, dimethyl sulfoxide), which has a fluctuating valence due to two mobile d-electrons in its atomic layer shell. The rate of electron transfer of [Fe14] complex demonstrates the Arrhenius-type temperature dependence in the nanosized spheric surface, wherein high-spin centers are ferromagnetically coupled, producing an S = 14 ground state. The electron-hopping rate at room temperature is faster than the time scale of Mössbauer measurements (, Fast intermetallic electron transfer is expected in principle in nanozised transition metal complexes, but has been prevented by the bridging ligands. Here the authors synthesize a mixed-valence iron metal-ligand nanocluster with cyanide bridges, showing extended delocalized electronic structure

The crystallographic and physical properties of the recently discovered filled skutterudite superconductor ${\mathrm{SrOs}}_{4}{\mathrm{P}}_{12}$, synthesized by a high-pressure and -temperature technique, are studied by measuring electrical resistivity, specific heat, and magnetization, and by performing electronic band calculations. X-ray powder diffraction with Rietveld refinement indicates that the lattice parameter of ${\mathrm{SrOs}}_{4}{\mathrm{P}}_{12}$ is 8.093(2) \AA{} and that fractional coordinates of the P site are [0, 0.3607(9), 0.1450(9)], which is also confirmed by calculations based on density functional theory. The electrical resistivity indicates a metallic nature of ${\mathrm{SrOs}}_{4}{\mathrm{P}}_{12}$, which is consistent with the density of states at Fermi energy with 7.5 (states/eV)/f.u. deduced from the electronic band calculations. The Sommerfeld coefficient $\ensuremath{\gamma}$ and Einstein temperature $\ensuremath{\theta}{}_{\mathrm{E}}$ of ${\mathrm{SrOs}}_{4}{\mathrm{P}}_{12}$ are deduced as $\ensuremath{\gamma}\ensuremath{\sim}26\phantom{\rule{4pt}{0ex}}\mathrm{mJ}/{\mathrm{mol}\phantom{\rule{0.16em}{0ex}}\mathrm{K}}^{2}$ and $\ensuremath{\theta}{}_{\mathrm{E}}\ensuremath{\sim}150$ K, respectively. A larger isotropic atomic displacement parameter ${U}_{\mathrm{eq}}$ of Sr compared to other atomic species as obtained from a Rietveld analysis and a specific heat anomaly around 30 K refers to anharmonic lattice vibrations of Sr in ${\mathrm{SrOs}}_{4}{\mathrm{P}}_{12}$. ${\mathrm{SrOs}}_{4}{\mathrm{P}}_{12}$ exhibits two superconducting transitions at ${T}_{\mathrm{c}1}=1.6$ K and ${T}_{\mathrm{c}2}=1.0$ K. Specific-heat data indicate that the observed superconductivity is of bulk nature with approximate volume fractions of $27%$ and $38%$ for superconductivity at ${T}_{\mathrm{c}1}$ and ${T}_{\mathrm{c}2}$, respectively. The electrical resistivity under field and pressure as well as the specific heat under field indicate that ${T}_{\mathrm{c}1}$ is sensitive to the magnetic field and ${T}_{\mathrm{c}2}$ is sensitive to pressure. The results show that ${\mathrm{SrOs}}_{4}{\mathrm{P}}_{12}$ is an $s$-wave weakly coupled superconductor with an electron-phonon mass enhancement ${\ensuremath{\lambda}}_{\text{ep}}\ensuremath{\sim}0.47$.

Geometrically frustrated kagome-lattice antiferromagnets have received much attention because of their exotic magnetic behaviors. Here we report the synthesis, structure, and magnetism of an $S=5/2$ quasiclassical new spin kagome compound. Polycrystalline compounds of $\mathrm{M}{\mathrm{g}}_{x}\mathrm{M}{\mathrm{n}}_{4\ensuremath{-}x}{(\mathrm{OH})}_{6}\mathrm{C}{\mathrm{l}}_{2}$, with a nominal ideal chemical formula of $\mathrm{MgM}{\mathrm{n}}_{3}{(\mathrm{OH})}_{6}\mathrm{C}{\mathrm{l}}_{2}$, have been successfully synthesized by selectively substituting the triangular-lattice-plane $\mathrm{M}{\mathrm{n}}^{2+}$ with nonmagnetic $\mathrm{M}{\mathrm{g}}^{2+}$. The compounds studied crystallize in rhombohedral structure in space group $R\text{\ensuremath{-}}3m$, in a similar crystal structure to the much-researched quantum spin liquid candidates herbertsmithite $\mathrm{ZnC}{\mathrm{u}}_{3}{(\mathrm{OH})}_{6}\mathrm{C}{\mathrm{l}}_{2}$ and tondiite $\mathrm{MgC}{\mathrm{u}}_{3}{(\mathrm{OH})}_{6}\mathrm{C}{\mathrm{l}}_{2}$. Antiferromagnetic transition below ${T}_{\mathrm{N}}\ensuremath{\sim}8\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and a 120\ifmmode^\circ\else\textdegree\fi{} nearest-neighbor spin ordering confined in the kagome plane with positive spin chirality have been revealed by magnetic susceptibility measurements and neutron diffraction experiment. The obtained value of critical exponent $\ensuremath{\beta}=0.35$ agrees with a three-dimensional Heisenberg spin model. The present work suggests the intrinsic nature of long-range order in classical Heisenberg kagome aniferromagnet and provides a classical reference system to quantum kagome antiferromagnets.

Doping ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ with Ti stabilizes the corundum paramagnetic metallic phase and restricts the transition to the monoclinic antiferromagnetic insulating phase at lower temperatures. In this study, we investigated the dependence of phase stability on Ti concentration for ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ nanocrystals as small as 20 nm. Ti doping of several percent induces a high-temperature insulating phase preserving the magnetic transition without the crystal symmetry change. The emergence of the insulating phases, which are peculiar to this crystal size, can be attributed to the enhancement of the on-site Coulomb interaction $U$ and increased mixing between ${a}_{1g}$ and ${e}_{g}^{\ensuremath{\pi}}$ states accompanied by characteristic lattice parameter changes in the high Ti doping region.

We studied hydrogen (H) and deuterium (D) impurity effects of superconducting Josephson current flowing through the superconductor-constriction-superconductor Josephson junctions (ScS-JJ). When H or D impurities are adsorbed on the surface of the ScS-JJ prepared by niobium or lead, many spike-like peaks with almost the same spacing appear inside the superconducting gap in addition to anomalies owing to the multiple Andreev reflection in the differential conductance spectra. The spacing between the adjacent peaks is independent of the temperature variation. These indicate that H or D impurities adsorbed on the JJ are sources of noise for the Josephson current.

We have performed the differential conductance (dI/dV) measurements of palladium (Pd) nanoconstrictions made by a mechanically controllable break junction technique to examine the origin of Fano resonance observed in atomic sized contacts of ferromagnetic metals such as Ni. As a quasimagnetic metal of Pd undergoing ferromagnetic transition by downsizing, the dI/dV spectra exhibit zero-bias anomalies with a dip, peak or asymmetric shape and are well-fitted by the Fano formula. Moreover, the amplitude of the anomalies varies with the temperature in logarithmic scale, suggesting that the origin of the anomaly is caused by the Kondo effect. These results indicate that the appearance of Kondo effect would be ubiquitous in ferromagnetic atomic scale contacts.

We fabricated quasiantiferromagnetic (quasi-AFM) layers with alternating antiparallel magnetization in the neighboring domains via 90° magnetic coupling through an Fe-O layer. We investigated the magnetic properties and the relationship between the magnetic domain size and the 90° magnetic coupling via experiments and calculations. Two types of samples with a Ru buffer and a (Ni80Fe20)Cr40 buffer were prepared, and we found that with the NiFeCr buffer, the sample has a flatter Fe-O layer, leading to stronger 90° magnetic coupling and a smaller domain size compared with the Ru buffer sample. This trend is well explained by the bilinear and biquadratic coupling coefficients, A12 and B12, in Landau–Lifshitz–Gilbert simulations, suggesting the possibility of using both AFM and FM properties by controlling the quasi-AFM domain size.

As practical applications of superconductivity have been made in electric power engineering, the breakdown voltage superconductor coolants, such as liquid helium or supercritical helium, have been needed intensively. Furthermore, in our discharge experiment in liquid helium to search for a novel carbon nanotube structure, it was predicted that the breakdown voltage was much higher. So, using the metal spherical electrodes, d.c. breakdown voltages in 4.2K gaseous helium (just above the liquid helium) and in liquid helium have been measured. As a result of the experiment, it was observed that the value is several times larger. Moreover, it found that there was no difference in the discharge phenomenon before and after the superfluid transition temperature.

We report a simple and accurate method to address the inevitable radiative heat loss in the Thomson coefficient measurement. The additional steps required are the measurement of the Joule heat arising from the ac current, measurement of the electrical resistance of the sample, and calculation of the ratio of the two measurement signals arising from the Joule and Thomson effects. The underlying concept is that most of the radiative heat loss that occurs during the measurement of Joule and Thomson heats can be compensated for by calculating the ratio of the two signals. This is because the heat loss during the Joule heat measurement will be highly similar to that during the Thomson heat measurement. Heat transfer analysis indicates that radiative heat loss is reduced by at least a factor of six. Once the Thomson coefficient is measured, accurate Seebeck and Peltier coefficients can be obtained in a single run. This approach was demonstrated by performing measurements on fine platinum wires in the temperature range of 80 K–300 K. The difference between the compensated and uncompensated curves became significant as the temperature increased; moreover, this difference was proportional to the cube of the temperature for a long fine-wire sample, where there is substantial radiative heat loss. Thus, the proposed approach is completely different from a conventional one, wherein the measurement accuracy degrades owing to inevitable radiative heat loss without prior knowledge of the thermal conductivity and emissivity of the sample.

We studied the dependence of the electronic specific heat Cel/T on the magnetic field up to H = 8 T in a dilute quadrupolar compound Pr0.05La0.95Pb3 with a non-Kramers Γ3 doublet in the crystal-ele...

The superconductivity of palladium–hydride (Pd–H) system was discovered by Skoskiewicz in 1972. Thereafter, many studies have been carried out on Pd–H and palladium deuteride (Pd–D) systems along w...

The intrinsic properties of superconductors enable the direct determination of the absolute Seebeck coefficient at low temperature due to the disappearance of the Seebeck effect to obey the Meissner effect. We report a precision absolute Seebeck coefficient measurement for the fine Pt sample determined using the high-Tc YBa2Cu3O7-x (YBCO) superconductor as a reference and an analysis of the measurement uncertainty. To make a precision measurement and aid in the verification of the uncertainty components, we developed a cryostat system that enables temperature control in a stable manner. The expected performance of the reference superconductor yielded a zero value well below Tc, which was validated by a superconductor-superconductor thermocouple experiment. Uncertainty analysis shows that the main limiting factor for this measurement is the accuracy of the temperature difference measurement using the resistance temperature sensors, along with its analog noise. We obtained values of S = 5.6 ± 0.2 µV/K with a relative expanded uncertainty of 3% at 80 K and precisely compared the Pt value with that determined by the high-Tc Bi2Sr2Ca2Cu3O8+δ (Bi-2223) superconductor, which has a higher Tc. We found that there was no difference between the Seebeck coefficient values obtained from the YBCO and Bi-2223 references up to its Tc within the expanded measurement uncertainties of 0.3 µV/K (2σ). These results provide accurate validation that the high-Tc superconductor is a useful reference up to the liquid nitrogen temperature.

Quantum spins on a triangular lattice may bring out intriguing and exotic quantum ground states. Here we report a magnetodielectric system of CuOHCl wherein $S=1/2\mathrm{C}{\mathrm{u}}^{2+}$ spins constitute a two-dimensional triangular lattice with the layers weakly coupled via Cl-H-O bonding. Despite strong magnetic interactions, as expected from the relatively high value of ${\ensuremath{\theta}}_{\mathrm{CW}}=\ensuremath{-}100\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, antiferromagnetic transition occurred at ${T}_{N}=11\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, followed by an uprising turn of the magnetic susceptibility below \ensuremath{\sim}7 K. Neutron-diffraction experiment revealed a coplanar spin structure on the triangular lattice below the ${T}_{N}$, with each spin pointing toward the center of a triangle. Of the three spins on a triangle, two are antiparallel and the third one is angled ${120}^{\ensuremath{\circ}}$ to the antiparallel spins. A concerted effect of geometric frustration in the triangular lattice and superexchange interactions through a zig-zag path via double Cu-O-Cu and double Cu-Cl-Cu bridges counted for this spin arrangement. Further investigation using dielectric constant and heat capacity measurements, as well as a microscopic probe of muon spin rotation, revealed a magnetodielectric effect and the possibility of multiferroic transition at ${T}^{*}\ensuremath{\sim}5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, which is suspected to be in close relation to geometric frustration in this triangular lattice. The present paper presents a magnetodielectric system on a two-dimensional triangular lattice with chemical stoichiometry. It can also serve as a rare reference to the hotly debated quantum spin-orbital liquid compound $\mathrm{LiNi}{\mathrm{O}}_{2}$.

Fedotovite K_{2}Cu_{3}O(SO_{4})_{3} is a candidate of new quantum spin systems, in which the edge-shared tetrahedral (EST) spin clusters consisting of Cu^{2+} are connected by weak intercluster couplings forming a one-dimensional array. Comprehensive experimental studies by magnetic susceptibility, magnetization, heat capacity, and inelastic neutron scattering measurements reveal the presence of an effective S=1 Haldane state below T≅4 K. Rigorous theoretical studies provide an insight into the magnetic state of K_{2}Cu_{3}O(SO_{4})_{3}: an EST cluster makes a triplet in the ground state and a one-dimensional chain of the EST induces a cluster-based Haldane state. We predict that the cluster-based Haldane state emerges whenever the number of tetrahedra in the EST is even.

Spin behaviors on kagome lattices have received increased attention because of their exotic magnetic states. Here, we report magnetic ordering in the $S=2$ kagome antiferromagnet $\mathrm{MgF}{\mathrm{e}}_{3}{(\mathrm{OH})}_{6}\mathrm{C}{\mathrm{l}}_{2}$. The compound has been synthesized by selectively replacing the magnetic ions in the triangular planes of its parent compound of deformed pyrochlore $\mathrm{F}{\mathrm{e}}_{2}{(\mathrm{OH})}_{3}\mathrm{Cl}$ with nonmagnetic Mg. Whereas $\mathrm{F}{\mathrm{e}}_{2}{(\mathrm{OH})}_{3}\mathrm{Cl}$ showed antiferromagnetic order below ${T}_{\mathrm{N}}=8.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ with persistent spin fluctuations, $\mathrm{MgF}{\mathrm{e}}_{3}{(\mathrm{OH})}_{6}\mathrm{C}{\mathrm{l}}_{2}$ showed an antiferromagnetic transition at an enhanced ${T}_{\mathrm{N}}$ value of 9.9 K. Susceptibility, high-field magnetization, and neutron-diffraction studies suggest that $\mathrm{MgF}{\mathrm{e}}_{3}{(\mathrm{OH})}_{6}\mathrm{C}{\mathrm{l}}_{2}$ is a Heisenberg-like spin system with a ${120}^{\ensuremath{\circ}}$ nearest-neighbor spin structure confined in the kagome plane and spin-vector chirality of $q=\ensuremath{-}1$ below ${T}_{\mathrm{N}}$. Muon spin-rotation/-relaxation studies demonstrate that the persisting spin fluctuations are suppressed relative to $\mathrm{F}{\mathrm{e}}_{2}{(\mathrm{OH})}_{3}\mathrm{Cl}$. The present paper reports the experimental realization of an $S=2$ kagome antiferromagnet, highlighting a real system with a quasiclassical Heisenberg spin, which may also be a valuable reference system for quantum Heisenberg kagome antiferromagnets.

$\mathrm{G}{\mathrm{d}}_{2}\mathrm{S}{\mathrm{n}}_{2}{\mathrm{O}}_{7}$ and $\mathrm{G}{\mathrm{d}}_{2}\mathrm{T}{\mathrm{i}}_{2}{\mathrm{O}}_{7}$ have been regarded as good experimental realizations of the classical Heisenberg pyrochlore antiferromagnet with dipolar interaction. The former was found to adopt the Palmer-Chalker state via a single, first-order transition at ${T}_{\mathrm{N}}\ensuremath{\approx}1\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, while the latter enters a distinct, partially ordered state through two successive transitions at ${T}_{\mathrm{N}1}\ensuremath{\approx}1\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and ${T}_{\mathrm{N}2}=0.75\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. To shed more light on their distinct magnetic ground states, we have synthesized two more gadolinium-based pyrochlore oxides, $\mathrm{G}{\mathrm{d}}_{2}\mathrm{G}{\mathrm{e}}_{2}{\mathrm{O}}_{7}$ and $\mathrm{G}{\mathrm{d}}_{2}\mathrm{P}{\mathrm{t}}_{2}{\mathrm{O}}_{7}$, under high-pressure conditions and performed detailed characterizations via x-ray powder diffraction, dc and ac magnetic susceptibility, and specific heat measurements down to 100 mK. We found that both compounds enter a long-range antiferromagnetically ordered state through a single, first-order transition at ${T}_{\mathrm{N}}=1.4\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for $\mathrm{G}{\mathrm{d}}_{2}\mathrm{G}{\mathrm{e}}_{2}{\mathrm{O}}_{7}$ and ${T}_{\mathrm{N}}=1.56\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for $\mathrm{G}{\mathrm{d}}_{2}\mathrm{P}{\mathrm{t}}_{2}{\mathrm{O}}_{7}$, with the specific heat anomaly similar to that of $\mathrm{G}{\mathrm{d}}_{2}\mathrm{S}{\mathrm{n}}_{2}{\mathrm{O}}_{7}$ rather than $\mathrm{G}{\mathrm{d}}_{2}\mathrm{T}{\mathrm{i}}_{2}{\mathrm{O}}_{7}$. Interestingly, the low-temperature magnetic specific heat values of both $\mathrm{G}{\mathrm{d}}_{2}\mathrm{G}{\mathrm{e}}_{2}{\mathrm{O}}_{7}$ and $\mathrm{G}{\mathrm{d}}_{2}\mathrm{P}{\mathrm{t}}_{2}{\mathrm{O}}_{7}$ were found to follow nicely the ${T}^{3}$ dependence as expected for a three-dimensional antiferromagnet with gapless spin-wave excitations. We have rationalized the enhancement of ${T}_{\mathrm{N}}$ in terms of the reduced Gd-Gd distances for the chemically pressurized $\mathrm{G}{\mathrm{d}}_{2}\mathrm{G}{\mathrm{e}}_{2}{\mathrm{O}}_{7}$ and the addition of extra superexchange pathways through the empty $\mathrm{Pt}\ensuremath{-}{e}_{g}$ orbitals for $\mathrm{G}{\mathrm{d}}_{2}\mathrm{P}{\mathrm{t}}_{2}{\mathrm{O}}_{7}$. Our current study has expanded the family of gadolinium-based pyrochlores and permits us to achieve a better understanding of their distinct magnetic properties in a more comprehensive perspective.

The Seebeck coefficient is the most widely measured property specific to thermoelectric materials. The absolute Seebeck coefficient S determined from the Thomson effect is highly sensitive to systematic errors incurred in the determination of the material thermal conductivity and geometry and heat loss from the sample to surroundings caused by temperature differences. Here, we report a technique for the precision measurement of S based on the Thomson effect using an ac-dc technique. This technique utilizes accurate equivalent-amplitude ac and dc currents, which can eliminate the need for acquiring accurate thermal conductivity and geometry values. These parameters can be replaced by the precisely and readily measurable parameters of electrical resistance and temperature changes caused by the Joule effect. The correction term of the heat loss owing to heat transfer via the thermocouple vanishes upon calculating the ratio of the measured temperature changes for both ac and dc excitations. We obtain an S value of -4.8 μV/K ± 0.2 μV/K at a temperature of 300 K for platinum, which is most widely used as a reference, with an expanded relative uncertainty of 4% (2σ). The obtained S value of Pt is closely consistent with that obtained from the conventional method using the Thomson effect within the uncertainty, and importantly, the measurement uncertainty improves to an acceptable level, which is four times more precise.

We studied the superconducting properties of Pd hydride and deuteride prepared by a low temperature absorption method using in situ magnetization measurements down to T = 0.5 K. The absorption was ...

The Gd–Ho series of lanthanide ferromagnets, which includes gadolinium (Gd), terbium (Tb), dysprosium (Dy), and holmium (Ho), undergoes similar structural transitions, e.g., the hcp→Sm-type→dhcp→fcc transitions, under pressure. Through high-field DC magnetic measurements and structural analyses, we found that the ferromagnetic moments disappeared at a specified critical pressure, which resulted in volume shrinkage of 16.7±1.7% for each ferromagnet. The results of the present study suggest that the disappearance of the ferromagnetic moments of Gd–Ho under pressure could be understood within the framework of a band picture related to volume shrinkage.

We have studied the low temperature properties of PrPb3 and PrInAg2 with the crystal-electric-field ground state of a non-Kramers Γ 3 doublet diluted by non-magnetic La ions to examine the correlation between the Γ 3 quadrupolar moments and the conduction electrons. In PrxLa1−xPb3, a non-Fermi liquid (NFL) behavior is observed at Pr concentrations of x ≤ 0.05 . The specific heat C / T increases monotonically below T = 1.5 K, which can be scaled with a characteristic temperature T ∗ defined at each concentration x. Application of magnetic field raises C / T rapidly, which demonstrates the presence of the residual entropy at lower temperatures. In PrxLa1−xInAg2, NFL behavior is confirmed for x = 0.05 and 0.1 in the susceptibility below 15 K and in the specific heat below 7 K. It is supposed that the Kondo effect arising from the correlation between the dilute Γ 3 moments and the conduction electrons gives rise to NFL behavior in both systems.

We have attempted to grow single crystals of Ce-Ni-Ge ternary system having layered structure. Several polycrystalline samples, CeNiGe, (2 < x < 3), Ce 3 Ni x Ge y (1.6 < x < 2, 6.5 < y < 8.5) and Ce 2 NiGe 6 , were prepared by an arc-melting of constituent elements. All samples grown by the Czochralsky method are found to contain the phase of the orthorhombic CeNiGe 2 type structure. A Rietveld method was applied to analyze the crystal structure of CeNiGe 2.2 using X-ray powder diffraction data at room temperature. The refined lattice parameters were a = 4.260 A, b = 16.81 A and c = 4.209 A with the space group Cmmm. The temperature dependence of magnetic susceptibility showsa significant variation in the magnetic properties depending on the concentration of Ge, that is, magnetic phase transition temperature depends on starting materials. It may come from the fact that the magnetic property relies on a structural homogeneity and a stoichiometry.

Specific heat measurements down to 120mK have been performed on a quasi-one-dimensional $S=1/2$ spin-gapped system (CH$_3$)$_2$NH$_2$CuCl$_3$ in a magnetic field up to 8 T. This compound has a characteristic magnetization curve which shows a gapless ground state and a plateau at 1/2 of the saturation value. We have observed a spontaneous antiferromagnetic ordering and a field-induced one below and above the 1/2 plateau field range, respectively. The field versus temperature phase diagram is quite unusual and completely different from those of the other quantum spin systems investigated so far. In the plateau field range, a double-structure in the specific heat is observed, reflecting the coexistence of ferromagnetic and antiferromagnetic excitations. These behaviors are discussed on the basis of a recently proposed novel quantum spin chain model consisting of weakly coupled ferromagnetic and antiferromagnetic dimers., Comment: 4 pages, 3 figures, submitted to J. Phys. Soc. Jpn

The low-temperature properties of Pr x La 1- x InAg 2 have been studied for a wide concentration range of Pr ions between 0≤ x ≤0.6. The susceptibility above T =15 K is well reproduced by the crystal-electric-field level scheme with a non-Kramers Γ 3 doublet in the ground state for each concentration, while that below T =15 K shows a non-Fermi-liquid behavior with a logarithmic temperature dependence. The temperature dependence of the specific heat C / T shows a monotonic enhancement below T =10 K, which can be scaled by a characteristic temperature T * defined at each concentration. These results suggest that the anomalous low-temperature properties are understood as the single-ion nature of Γ 3 quadrupolar moments. The origin of the anomalous properties is discussed in connection with the quadrupolar Kondo effect arising from the correlation between the Γ 3 moments and the conduction electrons.

Pressure effects on the magnetic properties of the triangular lattice Heisenberg antiferromagnet CsNiCl3 have been studied through heat capacity measurements up to the pressure of 6.6 kbar. With increasing pressure, two successive phase transitions at TN1 = 4.74 K and TN2 = 4.24 K at 0 kbar, which result from a small Ising-type anisotropy of S = 1 moments on Ni2+ ions, shift to higher temperatures in proportion to the pressure. Moreover, the pressure dependence of the entropy indicates that the intermediate phase AF1 (TN2

The doping effect of paramagnetic organic radical impurities ( p -CyDTV) on the organic spin–Peiels (SP) system of p -CyDOV (3-(4-cyanophenyl)-1,5-dimethyl-6-oxoverdazyl; the SP transition temperature T SP =15.0 K) was studied by the heat capacity measurement down to 0.1 K. At low temperatures below 1 K, quite a sharp heat capacity peak was detected for each system with small impurity concentration ( x ) at the temperature T N ( x ); T N (0)=0.135 K (±0.002 K), T N (0.01)=0.290 K and T N (0.07)=0.164 K. The appearance of the peak for the system with x =0 is considered to be due to minute and inevitable impurities in the pure p -CyDOV. From the dependence of T N ( x ), T N (0)< T N (0.01), and the heat capacity behavior on x , the peaks for x =0 and 0.01 are explained to be accompanied with the three-dimensional (3D) antiferromagnetic (AFM) transition in the SP phase. While the decrease of T N ( x ) for higher impurities x =0.07 than that for x =0.01 may be interpreted as merely a 3D AFM transition from th...

Heat capacity studies were performed for the doped verdazyl radical crystals, ( p -CyDOV) 1− x ( p -CyDTV) x ( x =0, 0.01, and 0.07), to clarify the effect of magnetic impurity ( p -CyDTV) on the spin-Peierls (SP) transition ( T SP =15.0 K) of 3-(4-cyanophenyl)-1,5-dimethyl-6-oxoverdazyl ( p -CyDOV) radical crystal, where the >C O group in p -CyDOV is replaced by the >C S group in p -CyDTV. The antiferromagnetic (AFM) transitions were observed at T N =0.135, 0.290, and 0.164 K for the crystals with x =0, 0.01, and 0.07, respectively, indicating the coexistence of AFM order and SP state in the systems with x =0 and 0.01, and the appearance of the single phase of AFM order in the system with x =0.07 below T N =0.164 K. However, the heat capacity anomaly associated with the SP transition was not found at T SP =15.0 K for the pure p -CyDOV crystal ( x =0), whereas the anomalous broad peak in the heat capacity was observed at T ′ SP =5.6 K. The entropy consumption in the above broad peak was about 3% of the total spin entropy R ln 2, suggesting that this transition may relate to SP transition. The pressure induced by the solidification of the Apiezon-N grease, which was used as the thermal binder for the heat capacity measurement, at low temperature may affect the shift of the SP transition temperature. The doping effects for the organic SP system ( p -CyDOV), which include the temperature ( T : T SP and T N )—impurity ( x ) phase diagram, are similar to those for the inorganic SP system (CuGeO 3 ), although the one-dimensionality, i.e., ∣ zJ ′/ J ∣≅6×10 −4 , in the organic p -CyDOV system is much higher than that (∼10 −1 ) in the inorganic CuGeO 3 system, where zJ ′ and J are inter- and intra-chain exchange interactions. This work is the first report of the heat capacity study of the doping effect on the organic SP transition system.

The pressure effects on an S = 1 Haldane compound Ni(C 5 H 14 N 2 ) 2 N 3 (PF 6 ) (NDMAP) have been investigated through the magnetic susceptibility (χ) measurements using single crystalline sample...

Magnetic measurements have been performed to investigate random-bond effects on a spin-ladder system. We synthesize a random mixture compound Cu 2 (C 5 H 12 N 2 ) 2 (Cl 1− x Br x ) 4 which is expected to form a spin ladder with random-exchange legs and rungs. The magnetic properties of the compound are rather different from those of the pure systems. Paramagnetic divergence is significantly observed for the susceptibility at low temperatures and the magnetization appears even at low fields. The results suggest that the ground state of the random-bond ladder is a Griffiths phase.