Hajime Ishikawa 교수

We have synthesized high-quality single crystals of volborthite, a seemingly distorted kagome antiferromagnet, and carried out high-field magnetization measurements up to 74 T and ^{51}V NMR measurements up to 30 T. An extremely wide 1/3 magnetization plateau appears above 28 T and continues over 74 T at 1.4 K, which has not been observed in previous studies using polycrystalline samples. NMR spectra reveal an incommensurate order (most likely a spin-density wave order) below 22 T and a simple s

Spin-orbit coupling of as large as a half eV for electrons in $5d$ orbitals often gives rise to the formation of spin-orbital entangled objects, with the effective total angular momentum ${J}_{\mathrm{eff}}$. Of particular interest are the ${J}_{\mathrm{eff}}=3/2$ states realized in $5{d}^{1}$ transition metal ions surrounded by an anion octahedron. The pure ${J}_{\mathrm{eff}}=3/2$ quartet does not have any magnetic dipolar moment $(\ensuremath{\langle}M\ensuremath{\rangle}=0)$ but hosts hidden

THIS PAPER describes the use of normally-off type GaAs MESFETs for low power and high speed logic gates. In a study, a 13-stage ring oscillator was built in a monolithic form and successfully tested. The power-speed product per gate was as small as 26 fJ.

Electronic properties of the single crystal of GdV6Sn6, where non-magnetic V-kagome layers are separated by magnetic Gd-triangular lattice, are investigated. GdV6Sn6 exhibits unique magnetotransport properties at low-temperature such as non-linear Hall resistivity and increase of resistance R in magnetic field H as R ~ H^0.75 up to 56 T with Shubnikov-De Haas oscillations. Investigation of the non-magnetic analogue YV6Sn6 and the first principles calculations reveal these properties are relevant

A new type of magnetically frustrated lattice is found in the layered fluoride NaBa2Mn3F11. A kagome-type array of regular triangles composed of Mn2+ ions (spin 5/2) deforms so as to generate the next-nearest-neighbor interaction J2 between three out of six spins in the hexagon of a normal kagome lattice, in addition to the nearest-neighbor interaction J1. As a function of |J2/J1|, this lattice can interconnect the kagome (J2 = 0) and the triangular (J2 = J1) lattices and thus is called the kago

Magnetic properties of $A\mathrm{MoOP}{\mathrm{O}}_{4}\mathrm{Cl}$ $(A=\mathrm{K},\phantom{\rule{0.28em}{0ex}}\mathrm{Rb})$ with $\mathrm{M}{\mathrm{o}}^{5+}$ ions in the $4{d}^{1}$ electronic configuration are investigated by magnetization, heat capacity, and nuclear magnetic resonance (NMR) measurements on single crystals, combined with powder neutron diffraction experiments. The magnetization measurements reveal that they are good model compounds for the spin-1/$2{J}_{1}\text{\ensuremath{-}}{

Structural and magnetic properties of cubic spinel selenides GaM_{4}Se_{8} (M=Nb, Ta), which are candidates for the molecular J_{eff}=3/2 Mott insulators, are investigated. The effective magnetic moments are reduced compared to the spin only value, indicating the presence of sizable spin-orbit coupling. GaNb_{4}Se_{8} and GaTa_{4}Se_{8} exhibit phase transitions into the nonmagnetic ground states with orthorhombic and tetragonal structures, respectively, which are robust against magnetic field u

Magnetic properties of an antiferromagnetic double perovskite oxide ${\mathrm{Ba}}_{2}{\mathrm{CaReO}}_{6}$, where ${\mathrm{Re}}^{6+}$ $(5{d}^{1})$ ions with large spin-orbit coupling are arranged on the face-centered-cubic lattice, are investigated using pulsed high magnetic field up to 66 T. Magnetization and magnetostriction measurements have revealed a magnetic field-induced phase transition at around 50 T. The phase transition accompanies a jump of magnetization and longitudinal magnetostr

A new polymorph of volborthite [tricopper(II) divanadium(V) heptaoxide dihydroxide dihydrate], Cu(3)V(2)O(7)(OH)(2)·2H(2)O, has been discovered in a single crystal prepared by hydrothermal synthesis. X-ray analysis reveals that the monoclinic structure has the space group C2/c at room temperature, which is different from that of the previously reported C2/m structure. Both structures have Cu(3)O(6)(OH)(2) layers composed of edge-sharing CuO(4)(OH)(2) octahedra, with V(2)O(7) pillars and water mo

Single crystals are indispensable for understanding the fundamental properties of materials, although obtaining them are often challenging. To investigate the magnetic properties of a kagome-lattice antiferromagnet, we have performed a topochemical crystal transformation from a copper mineral volborthite with a distorted kagome lattice into another copper mineral vesignieite with an almost perfect kagome lattice. A millimeter-sized crystal of vesignieite, which is difficult to prepare via direct

We report magnetic properties of a $4f$ honeycomb iodide $\mathrm{Sm}{\mathrm{I}}_{3}$ made up of edge-shared network of $\mathrm{Sm}{\mathrm{I}}_{6}$ octahedra. High temperature magnetic susceptibility indicates a ${\mathrm{\ensuremath{\Gamma}}}_{7}$ Kramers doublet ground state of ${\mathrm{Sm}}^{3+}(4{f}^{5})$ ions stabilized by the spin-orbit coupling and octahedral crystal electric field, which interact with a Sm-I-Sm bond angle of nearly ${90}^{\ensuremath{\circ}}$. Magnetization measureme

Performance of a 4K static MOS RAM was improved significantly with utilization of low-resistance molybdenum-gate process instead of conventional polysilicon-gate process. A typical access time of 27 ns was achieved with a low power consumption of 250 mW when the RAM was operated at supply voltage of 5 V and TTL-compatible I/O levels. Signal propagation delay along the word line of the RAM was quite small as a result of the reduction in interconnection resistance. Several disadvantages of the Mo