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Katsumi Tanigaki

Publications and source records attributed to Katsumi Tanigaki.

4 recordsLinked to original sources
PubMed2006

Ferromagnetic ordering in a new nickel polyborate NiB12O14(OH)10.

A new nickel polyborate, NiB12O14(OH)10 was synthesized using boric acid as a flux. This material has two-dimensional borate layers with a quasi-square lattice of Ni2+. The Ni2+ ions locate in the plane of the two-dimensional layer, bridged through BnO(n+1) chains in the plane and connected with the three-membered ring borate groups out of the plane. The dc and ac magnetic susceptibility, magnetization and specific heat measurements show that this material undergoes a weak ferromagnetic phase transition at Tc = 5.8 K. At T < Tc, a metamagnetic phase transition is observed at about 5 T, associated by a spin-flop, suggesting the ferromagnetic ordering is induced by an antiferromagnetic interaction. A broad maximum in the ac susceptibility at TM = 23-24 K indicates an intermediate short-range ordering.

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PubMed2005

Soft x-ray spectroscopy of Ba24Ge100: electronic phase transition and Ba-atom rattling.

The electronic states of Ba24Ge100 are studied by soft x-ray photoelectron spectroscopy (XPS) at a high-energy photon factory. A large reduction in the density of states (DOS) at the Fermi level is clearly shown before and after the electronic phase transition at 200 K. The changes in the spectrum widths and the fine structures of the core-level Ba 4d spectra give a very reasonable indication of the Ba-atom rattlings in the clathrate polyhedra. On-resonance experiments using the excitation from Ba 3d to 4f levels display that the wave functions of Ba 5d and 6s orbitals give only a small contribution to make a Fermi surface through the hybridization with the Ge20 cluster orbitals. Importantly, reliable values of the DOS at the Fermi level NEF are successfully deduced, using two data sets of DOS obtained from high-resolution XPS and the total magnetic susceptibilities by a superconducting quantum interference device, to be 0.149 and 0.0427 states eV(-1) (Ge atom)(-1) for a high-temperature and for a low-temperature phase.

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PubMed2002

Close-packed C(70)(3-) phases - synthesis, structure, and electronic properties.

The high symmetry and resulting electronic degeneracy of the C(60)(3)(-) anion is viewed as the key molecular feature in the high superconducting transition temperatures of fulleride and oxidized fullerene systems. The experimental evaluation of this hypothesis requires the synthesis of face-centered cubic (fcc) trivalent fulleride anion salts derived from higher fullerenes such as C(70), which have thus far proved elusive with only stable A(1)C(70), A(4)C(70), and A(6)C(70) phases known. In this paper, we report the synthesis of fcc A(3)C(70) phases stabilized by size-matching the tetrahedral site with the sodium cation. The structures are strongly dependent on the cooling protocol due to the existence of metastable partially or completely orientationally disordered phases. EPR data indicate that the phases are metallic but not superconducting. The densities of states at the Fermi level appear too low to give superconductivity at above 5 K, consistent with recent observations that four electrons per C(70) anion are required for superconductivity. Size-matching on both the octahedral and tetrahedral sites is required for A(3)C(70) stability - K(2)CsC(70) is only stable at elevated temperature and Na(2)C(70) is unstable, the composition corresponding to C(70) and a sodium-rich trigonal phase.

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