Yutaka Itoh

Synthesis and Magnetic Properties of Ni3AlCx

The itinerant-electron ferromagnet Ni 3 Al and its carbon-intercalated compounds Ni 3 AlC x ( x = 0.01, 0.02, 0.04, 0.05, 0.08, and 0.1) were synthesized and investigated by magnetization measurements between 2 and 300 K with the magnetic field H up to 5 T and 27 Al NMR measurements at H = 7.4847 T. The Curie temperature is suppressed and disappears only by the carbon intercalation with x = 0.02. For the samples with x ≤0.02, the T 4/3 -temperature dependence of M s 2 ( M s : spontaneous magnetization) and χ 0 -1 (χ 0 : initial susceptibility) are newly observed, being consistent with the predication of the self-consistent renormalization theory of spin fluctuations for weak itinerant ferromagnets. The coupling constant between the 27 Al Knight shift and the bulk susceptibility of Ni 3 AlC 0.1 is three times larger than that of Ni 3 Al, suggesting the drastic change of the electronic state by the carbon intercalation.

Nano-tube-like surface structure in graphite anodes for lithium-ion secondary batteries

Abstract We report microstructures on the surface of graphite particles found in practicable carbon anodes by means of high-resolution transmission electron microscopy. The surfaces consist of “closed-edge” structures constructed in a similar manner as carbon nano-tube. We have also investigated the formation mechanism of these nano-structures using molecular dynamics simulations based on the Tersoff potential. From electrochemical measurements, the carbon anodes composed of these “closed-edge” structures show actually high battery performance with a large discharge capacity and a small irreversible capacity.

Hydroxyl Motion in Mg(OH)2

We report on pulsed 1H NMR studies of the hydroxyl OH groups in magnesium hydroxide Mg(OH)2 at 77–355 K at 42.5772 MHz. The Fourier-transformed NMR spectra show the superposition of broad and narrow components. The broad NMR spectrum is assigned to dipole-coupled protons on a rigid lattice in the bulk Mg(OH)2, while the narrow NMR spectrum is assigned to extrinsic protons, e.g., conduction protons facilitated by lattice defects. We found a monotonically decreasing linewidth of the broad NMR spectrum on heating. The monotonic decrease in the linewidth is associated with hopping protons around a threefold axis (rotational hydroxyl protons).

Extrinsic Proton NMR Studies of Mg(OH) 2 and Ca(OH) 2

We studied narrow 1H NMR spectra of Mg(OH)2 and Ca(OH)2 powders at 100–355 K and 42–59 MHz using pulsed NMR techniques. The Fourier transformed NMR spectra of the proton free-induction signals show the superposition of broad and narrow components, which can be assigned to immobile protons and extrinsic mobile protons, respectively. We found that a narrow spectrum develops on heating above about Tc = 260 K and widens above a Larmor frequency of about νc = 50 MHz for Mg(OH)2. The temperature-induced NMR spectrum and the characteristic frequency νc of 50 MHz are the noteworthy features of the nuclear spin fluctuation spectra of the extrinsic protons.

NMR study of : Antiferromagnetic vortex cores or Bragg glass?

We studied the vortex state of an oriented polycrystalline high-TcTc superconductor Tl2Ba2CuO6+δTl2Ba2CuO6+δ(Tc∼85K) by Tl205 NMR spin-echo technique. Although more than 10 years have passed since the sample was synthesized, no aging effects were found in the low-field magnetic susceptibility and the zero-field Cu63,65 nuclear quadrupole resonance spectrum. From Tl205 NMR spectra at 2xa0T, we observed vortex melting, vortex partial melting, imperfect vortex lattices, and the absence of static antiferromagnetic ordering at vortex cores.