Yoshinori Manmoto

Effects of Cooling Rate on Growth of Bi-2212 Superconducting Whiskers

Bi2Sr2CaCu2Ox (Bi-2212) superconducting whiskers have been prepared by using a melt-quenched glass precursor method and it has been reported that the glass precursor was necessary to the growth of the long whiskers. In this work to ascertain the necessity, the effects of the cooling rate of the melt on the growth of Bi-2212 whiskers were studied. Our experimental results indicated that the glass precursors were not needed for the whisker growth. In addition we report that long YBa2Cu3Ox whiskers of 1~3 mm in length can be prepared by melting and furnace cooling.

NMR Multiple-Quantum Transitions in a Double Rotating Coordinate System

The experimental observation of multiple-quantum transitions of Na nuclei in a NaCl single crystal by the rotary-saturation method is reported. Results are discussed by using a second quantization formalism and n -th order time-dependent perturbation in the second rotating frame.

NMR multiple-quantum processes in a doubly rotating frame in solids

Abstract Multiple-quantum transitions between nuclear spin Zeeman levels of fluorine nuclei in a CaF2 single crystal are studied by a rotary-saturation method in NMR. The theoretical studies are performed for the system consisting of spins interacting with each other through dipole-dipole coupling. The analysis of the behavior of nuclear magnetization, the second quantization of a perturbing field, and the calculation of the nth-order timedependent perturbation are all performed in the reference frame of a doubly rotating system. We found evidence that (1) one type of single spin-n quantum transitions is taking place, but another type of two spin-n quantum transitions is not confirmed yet in this crystal; (2) the linewidths of the multiple-quantum absorptions are extremely narrow at the magic angle but do not completely vanish because of the presence of a perturbing field; (3) the effects of the energy level mixing through the dipole-dipole interactions on the multiple-quantum transitions are negligible over a wide range around the magic angle; and (4) the inhomogeneity of the RF field used to quantize the spin system in the rotating frame affects considerably the results of the rotary-saturation experiments.