Tomoo Yamamura

Wheel-Shaped ErIIIZnII3Single-Molecule Magnet: A Macrocyclic Approach to Designing Magnetic Anisotropy

Single-molecule magnets (SMMs) are chemically and physically interesting compounds that exhibit hitherto unobserved magnetic properties. To prevent reversal of the molecular magnetic moment, the use of heavy lanthanide ions is becoming popular because of their large spin multiplicity and large magnetic anisotropies in the ground state. Lanthanide ions exhibit flexibility in magnetic anisotropy, which is another advantage of Ln-based SMMs that is attributable to the flexible design and control of the ligandfield (LF) anisotropy. These anisotropies are correlated through Stevens factor qm as B n m 1⁄4 Am r h iqm, where Bm denotes the mth-order magnetic anisotropy parameters (m is 2, 4, or 6 for lanthanide ions; n varies between 0 and m ; second-order terms of B2 and B 2 2 correspond to the axial and rhombic anisotropic parameters D and E), and Am r m h i denotes the LF anisotropy parameters. Therefore, Ln complexes have a wide scope in the synthetic design of anisotropic magnets. Although many complexes including one or more heavy lanthanide ions are reported to be SMMs, most of them were synthesized in a fortuitous manner without design of the magnetic anisotropy. We have demonstrated previously that an axial LF, whereby donor atoms with higher negative charges are located along the principal axis, induces a strong Ising-type anisotropy of Tb and Dy ions. This type of LF anisotropy is easily achieved in an accidental manner, and thus a wide variety of Tb and Dy SMMs have been reported. On the contrary, Er-based SMMs are rare. When the second-order anisotropy terms are dominant, magnetic anisotropy of the Er ion has opposite features to those of Tb and Dy ions, since the q2 parameter of the Er III

Electron-Transfer Kinetics of Np3 + ∕ Np4 + , NpO2 + ∕ NpO2 2 + , V2 + ∕ V3 + , and VO2 + ∕ VO2 + at Carbon Electrodes

Like vanadium redox couples (V 2 + /V 3 + and VO 2 + /VO + 2 ), neptunium is a good candidate for the active materials of a redox-flow battery because it possesses two isostructural and reversible redox couples (Np 3 + /Np 4 + and NpO + 2 /NpO 2 + 2 ). The standard rate constants k 0 of the neptunium electrode reactions were first determined at four types of carbon electrodes. The k 0 values for Np 3 + /Np 4 + and NpO + 2 /NpO 2 + 2 are 1.9 X 10 - 2 and 1.5 X 10 - 2 cm s - 1 , respectively, at the c plane of pyrolytic graphite [PG(c plane)] and also 1.4 × 10 - 2 and 2.1 × 10 - 2 cm s - 1 , respectively, at plastic formed carbon (PFC). The standard rate constants for the V 2 + /V 3 + and VO 2 + /VO + 2 electrode reactions were also first determined at PG(c plane) and PFC electrodes. The determined k 0 values are larger at the PFC electrode, k 0 = 5.3 × 10 - 4 and 8.5 × 10 - 4 cm s - 1 for V 2 + /V 3 + and VO 2 + /VO + 2 , respectively, than at the PG(c plane) electrode. There is about a 10 2 order of difference between the k 0 values of neptunium and vanadium ions, and this difference was discussed in reference to the homogeneous electron-exchange rate constants of these redox couples.

Electrochemical investigation of uranium β-diketonates for all-uranium redox flow battery

Abstract The redox flow battery using uranium as the negative and the positive active materials in polar aprotic solvents was proposed. In order to establish the guiding principle for the uranium compounds as the active materials, the investigation of uranium β-diketonate complexes was conducted on (i) the solubility of active materials, (ii) the electrode reaction of U(VI) and U(IV) β-diketonate complexes and (iii) the estimation of the open circuit voltage of the battery. The solubilities of higher than 0.8 mol dm −3 of U(VI) complexes and higher than 0.4 mol dm −3 of a U(IV) complex were obtained in the solvents. The electrode reactions of U(pta) 4 , UO 2 (dpm) 2 , UO 2 (fod) 2 and UO 2 (pta) 2 were first studied and the redox potentials of uranium β-diketonates were thermodynamically discussed. The open circuit voltage is estimated more than 1 V by using Hacac or Hdpm. The larger open circuit voltage is expected when a ligand with the larger basicity is used.

Linear trinuclear Zn(II)-Ce(III)-Zn(II) complex which behaves as a single-molecule magnet.

Linear Zn(II)-Ce(III)-Zn(II) complex, which involves only one 4f electron as a spin source, behaves as an SMM. Easy-axis magnetic anisotropy for the ground (2)F(5/2) state of Ce(III) was achieved by a uni-axial crystal field, which is formed with four phenoxo oxygens as axial donors with the other five oxygens as equatorial donors.

Magnetic relaxations arising from spin-phonon interactions in the nonthermally activated temperature range for a double-decker terbium phthalocyanine single molecule magnet.

Magnetic relaxations arising from spin-phonon interactions for a magnetically diluted double-decker terbium phthalocyanine single molecule magnet, dil1, in the nonthermally activated temperature range have been investigated. While the relaxation time, τ, is independent of the external static magnetic field, H(dc), in the high temperature range, where linear relationships between -ln τ and T(-1) are observed in the Arrhenius plot, magnetic field dependences for τ are observed in the lower temperature range. The τ(-1) vs H(dc) plot at 12 K fits the quadric curve when H(dc) < 12 kOe, while linear relationships are observed in the τ(-1) vs T plots in the temperature range of 12-20 K. These results indicate that the direct process is the dominant magnetic relaxation pathway in the nonthermally activated temperature range, while the contribution from the Raman process, if any, is not observable. We emphasize in this paper that the contribution from the thermal relaxation processes and the quantum tunneling of magnetizations (QTMs) to the experimentally observed magnetic relaxations must be evaluated carefully in order to avoid confusion between the thermal and quantum-mechanical relaxation pathways.

Giant and isotropic low temperature magnetocaloric effect in magnetic semiconductor EuSe

We present the giant and isotropic magnetocaloric effect (MCE) in antiferromagnetic semiconductor EuSe. Near the transition temperature TN = 4.6 K, the maximum value of the magnetic entropy change (−ΔSmmax) and the relative cooling power of EuSe for a field change of 5 T are evaluated to be 37.5 J kg−1 K−1 and 580 J kg−1, respectively, based on the magnetization and specific heat data. The −ΔSmmax value of EuSe obtained in this work is the largest among the low temperature (<20 K) magnetic refrigerant materials reported so far, which is even larger than that of the best known room temperature giant MEC materials.

Deactivation and luminescence lifetimes of excited uranyl ion and its fluoro complexes

Abstract The luminescence decay of uranyl fluoride complexes has been studied in broad fluoride concentration range. Biexponential decay were found with a shorter lifetime component varying between 1.7 and 19.1 μs, while a longer component is in the range from 49 to 156 μs. The fluoride saturated solution exhibits single exponential decay with a lifetime of 207 μs. The activation parameters for the decay of [UO2F]+ complex have been determined. The results have been compared to other studies and interpreted in terms of ligand exchange, which is proposed as a new deactivation pathway for excited uranyl fluoro complexes.

Light Lanthanide Complexes with Crown Ether and Its Aza Derivative Which Show Slow Magnetic Relaxation Behaviors

Two sets of isostructural Ln(III) mononuclear complexes, [Ln(NO3)3(18-crown-6)] (Ln = Ce (1), Pr (2), and Nd (3)) and [Ln(NO3)3(1,10-diaza-18-crown-6)] (Ln = Ce (4), Pr (5), and Nd (6)), were synthesized, and their slow magnetic relaxation behavior was investigated. Since Ln(III) ions are located in an axially stressed ligand field in both sets of complexes, they can exhibit single-molecule magnet (SMM) behavior owing to the oblate-type electronic distributions of the ground sublevels found in Ce(III), Pr(III), and Nd(III). Field-induced slow magnetic relaxation was observed for Ce(III) and Nd(III) complexes 1, 3, 4, and 6 under an applied bias dc field of 1000 Oe, whereas no slow relaxation was observed for Pr(III) complexes 2 and 5. The slow magnetic relaxation behavior of 1, 3, 4, and 6 was correlated with the even-numbered Jz sublevels of Ce(III) and Nd(III) ions, known as the Kramers system.

Chemical States in Oxide Films on Stainless Steel Treated in Supercritical Water Factor Analysis of X-Ray Photoelectron Spectra

A preliminary study of the corrosion films of stainless steel SUS304 was carried out by X-ray photoemission spectroscopy for supercritical water having no oxidant or reactant. The corrosion films produced by the supercritical water at 450°C and 50 MPa were compared with those by anodic polarization in H 2 SO 4 aqueous solution. The chemical states in the films were determined by factor analysis of Fe, Cr, and Ni 2p X-ray photoelectron spectra. Factor analysis of the passivated SUS304 surface was successfully carried out using four reference spectra, Fe metal, Fe 3 O 4 , Fe 2 O 3 , and FeOOH, with careful treatment excluding wustite Fe 1 - x O phase from the standpoint of thermochemistry. In the surface treated by supercritical water, the ratio of iron and nickel increased even when compared to the bulk composition of SUS304 and the major component of nickel was attributed to NiFe 2 O 4 . In contrast, the content of chromium decreased remarkably. This was explained by effective removal of CrO 2 - 4 and its protonated form, HCrO - 4 , which are predicted in the Pourbaix diagram prepared for chromium in supercritical water (450°C and 50 MPa).

Study on a nuclear fuel reprocessing system based on the precipitation method in mild aqueous solutions

AbstractA new reprocessing system for spent nuclear fuels based on a precipitation method is proposed to recover uranium and transuranium elements from spent nuclear fuels in high ratios and to achieve extreme safety without any potential dangers. Experiments were carried out for a simulated fuel solution containing uranium and 17 major elements. The main reprocessing processes are as follows: (a) dissolution of U02 fuel under mild conditions; (b) neutralization of the dissolved fuel solution with Na2C03-NaHC03 mixed solutions, followed by the separation of precipitated fission products by centrifugation; (c) separation of cesium by a precipitation method using a tetraphenylborate ion; and (d) recovery of uranium (U) as a precipitate of the hydrolyzed compound from an alkaline solution. As a result, 99.95% of the U was recovered with the least amount of fission products, i.e., 10-5 g or even less in the recovered 1 g of U with the only exceptions being zirconium and molybdenum.