arXiv subjects

Makoto Yoshida

Publications and source records attributed to Makoto Yoshida.

23 records · Page 2Linked to original sources

arXiv2011

Metal-Insulator Transition and Magnetic Order in the Pyrochlore Oxide Hg2Ru2O7

We report results of NMR experiments on the ruthenium oxide Hg2Ru2O7 with the pyrochlore structure, which exhibits a metal-insulator transition at TMI = 107 K. In the metallic phase above TMI, the nuclear spin-lattice relaxation rate 1/T1 and the Knight shift at the Hg sites follow the Korringa relation, indicating the absence of substantial spatial spin correlation. At low temperatures in the insulating phase, 99,101Ru-NMR signals are observed at zero magnetic field, providing evidence for a commensurate antiferromagnetic order. The estimated ordered moment is about 1 muB per Ru, much smaller than 3 muB expected for the ionic (4d)3plus configuration of Ru5plus. Thus the localized spin models are not appropriate for the insulating phase of Hg2Ru2O7. We also discuss possible antiferromagnetic spin structures.

cond-mat.str-el↗

arXiv2009

Universality and the zero-bias conductance of the single-electron transistor

The thermal dependence of the electrical conductance of the single-electron transistor (SET) in the zero-bias Kondo regime is discussed. An exact mapping to the universal curve for the symmetric Anderson model is established. Linear, the mapping is parametrized by the Kondo temperature and the charge in the Kondo cloud. Illustrative numerical renormalization-group results, in excellent agreement with the mapping, are presented.

cond-mat.mes-hall↗

arXiv2009

Magnetization "Steps" on a Kagome Lattice in Volborthite

Magnetic properties of the spin-1/2 kagome-like compound volborthite are studied using a high-quality polycrystalline sample. It is evidenced from magnetization and specific heat measurements that the spins on the kagome lattice still fluctuate at low temperature, down to T = 60 mK that corresponds to 1/1500 of the nearest-neighbor antiferromagnetic interaction, exhibiting neither a conventional long-range order nor a spin gap. In contrast, 51V NMR experiments revealed a sharp peak at 1 K in relaxation rate, which indicates that a certain exotic order occurs. Surprisingly, we have observed three "steps" in magnetization as a function of magnetic field, suggesting that at least four liquid-like or other quantum states exist under magnetic fields.

cond-mat.str-el↗

arXiv2008

Commensurate Itinerant Antiferromagnetism in BaFe2As2: 75As-NMR Studies on a Self-Flux Grown Single Crystal

We report results of 75As nuclear magnetic resonance (NMR) experiments on a self-flux grown single crystal of BaFe2As2. A first-order antiferromagnetic (AF) transition near 135 K was detected by the splitting of NMR lines, which is accompanied by simultaneous structural transition as evidenced by a sudden large change of the electric field gradient tensor at the As site. The NMR results lead almost uniquely to the stripe spin structure in the AF phase. The data of spin-lattice relaxation rate indicate development of anisotropic spin fluctuations of the stripe-type with decreasing temperature in the paramagnetic phase.

cond-mat.supr-con↗

arXiv2008

A Nuclear Magnetic Resonance Study on Rubrene-cobalt Nano-composites

We implemented a nuclear magnetic resonance (NMR) study on rubrene(C42H28)-Co nano-composites that exhibit an enhanced magnetoresistance (MR) ratio of 80%. The 59Co NMR spin echo experiment enabled clarification of the hyperfine field of Co at the interface between the ferromagnet and the molecules, which has not been investigated for molecular spintronics. An enhanced hyperfine field of the Co was observed in the rubrene-Co nano-composites, which may be related to the enhancement of the MR ratio. This study demonstrates the importance of microscopic investigation of the interface between molecules and ferromagnets that governs spin-dependent transport in molecular spin devices.

cond-mat.mtrl-sci↗