arXiv subjects

Makoto Hagiwara

Publications and source records attributed to Makoto Hagiwara.

5 recordsLinked to original sources

arXiv2021

Enhanced superconducting properties of double-chain based superconductor Pr$_{2}$Ba$_{4}$Cu$_{7}$O$_{15-δ}$ synthesized by citrate pyrolysis technique

We report the enhanced superconducting properties of double-chain based superconductor Pr$_{2}$Ba$_{4}$Cu$_{7}$O$_{15-δ}$ synthesized by the citrate pyrolysis technique. %In spite of the polycrystalline bulk samples, we obtained the higher residual resistivity ratios (10-12). The reduction heat treatment in vacuum results in the appearance of superconducting state with $T_\mathrm{c}$=22-24 K, accompanied by the higher residual resistivity ratios. The superconducting volume fractions are estimated from the ZFC data to be 50$\sim55\%$, indicating the bulk superconductivity. We evaluate from the magneto-transport data the temperature dependence of the superconducting critical field, to establish the superconducting phase diagram. The upper critical magnetic field is estimated to be about 35 T at low temperatures from the resistive transition data using the Werthamer-Helfand-Hohenberg formula. The Hall coefficient $R_{H}$ of the 48-h-reduced superconducting sample is determined to be -0.5$\times10^{-3}$ cm$^{3}$/C at 30 K, suggesting higher electron concentration. These findings have a close relationship with homogeneous distributions of the superconducting grains and improved weak links between their superconducting grains in the present synthesis process.

cond-mat.supr-con↗

arXiv2020

Nonmonotonic Pressure Dependence of the Lattice Parameter $a$ in the Quasi-one-dimensional Superconductor Pr$_2$Ba$_4$Cu$_7$O$_{15-δ}$

In the quasi-one-dimensional superconductor, Pr$_2$Ba$_4$Cu$_7$O$_{15-δ}$, we found that the lattice parameter, $a$ increased against pressure, starting at 2.0 GPa at approximately 300 K. This result suggests that the two-dimensional inter-conducting-chain interaction along the $a$ axis is most enhanced at approximately 2.0 GPa. To discuss the dimensionality, we also measured the resistance under magnetic fields up to 14 T, because magneto-resistance is induced when a system changes from one-dimensional to two-dimensional.

cond-mat.supr-con↗

arXiv2019

Formulating Manipulable Argumentation with Intra-/Inter-Agent Preferences

From marketing to politics, exploitation of incomplete information through selective communication of arguments is ubiquitous. In this work, we focus on development of an argumentation-theoretic model for manipulable multi-agent argumentation, where each agent may transmit deceptive information to others for tactical motives. In particular, we study characterisation of epistemic states, and their roles in deception/honesty detection and (mis)trust-building. To this end, we propose the use of intra-agent preferences to handle deception/honesty detection and inter-agent preferences to determine which agent(s) to believe in more. We show how deception/honesty in an argumentation of an agent, if detected, would alter the agent's perceived trustworthiness, and how that may affect their judgement as to which arguments should be acceptable.

cs.AI↗

arXiv2013

Effect of magnetic field on the superconducting phase in the electron-doped metallic double-chain compound Pr$_{2}$Ba$_{4}$Cu$_{7}$O$_{15-δ}$

We report the magnetotransport and $dc$ magnetic susceptibility of the polycrystalline samples of Pr$_{2}$Ba$_{4}$Cu$_{7}$O$_{15-δ}$, to examine the effect of magnetic field on the superconducting phase of the metallic CuO double chain. The resistive critical magnetic field is estimated to be about 21 T at low temperatures from the resistive transition data. On the other hand, the corresponding critical field determined from the magnetization measurements gives rise to a very low value of $\sim 0.3$T at 2 K. These discrepancies in the magnetic response between the resistivity and magnetization data are caused by disappearance of the magnetically shielding effect even in relatively lower fields. In spite of the observation of the resistive drop associated with the superconducting transport currents, the suppression of the diamagnetic signal is probably related to the superconductivity of quasi one-dimensional CuO double-chain. The behavior of Seebeck coefficient in the superconducting Pr$_{2}$Ba$_{4}$Cu$_{7}$O$_{15-δ}$ is discussed on the basis of the double chain model from the density functional band calculation.

cond-mat.supr-con↗

arXiv2012

Magnetization and transport properties in the superconducting Pr$_{2}$Ba$_{4}$Cu$_{7}$O$_{15-δ}$ with metallic double-chain

We have reported the effect of pressure on the magnetization, and transport properties in the nominal composition Pr$_{2}$Ba$_{4}$Cu$_{7}$O$_{15-δ}$ synthesized by a sol-gel technique. A reduction treatment of the as-sintered sample in vacuum causes higher superconductivity achieving $T_{c,on}=\sim 30$ K for $δ=0.94$. Application of hydrostatic pressure on the oxygen depleted sample enhances its onset temperature up to 36 K at 1.2 GPa, indicating the nearly optimum doping level of the charge carrier in comparison to the pressure dependence of lower $T_{c}$ samples with $δ=0.45$. Seebeck coefficient of the superconducting sample shows a metallic conduction, followed by a clear drop below $T_{c,on}$ and is in its temperature dependence below 100 K quite different from that of the non-superconducting one. This finding strongly suggests a dramatic change of the electronic state along the CuO double chain due to the reduction treatment for the appearance of superconductivity .

cond-mat.supr-con↗