arXiv subjects

Paul Ben Ishai

Publications and source records attributed to Paul Ben Ishai.

4 recordsLinked to original sources

arXiv2025

The Origin of Organic Magnetoresistance Using Time-Domain Magnetic Spectroscopy

Organic Magnetoresistance is defined as the change of resistance in an organic material, such as a conducting polymer, as a function of an imposed magnetic field. We demonstrate this effect in a Polypyrrole/ Polydimethylsiloxane complex by using a novel magnetic pulse system. The frequency spectrum of the current flowing through the sample reveals equally spaced reversed peaks in the current. We show that these peaks happen at the Lamour frequency for the dominant charge carrier of the system, namely polarons. This posits the origin Organic magnetoresistance as simple Rabi Oscillations rather than mechanisms based of bipolaron formation and singlet-triplet conversions. We directly estimate the effective polaronic mass in this complex. A semi classical theoretical approach is suggested to explain this effect as direct spin flipping in a time transient magnetic field. This is the first time that such an experimental approach has been applied in this field and the first time the effective polaronic mass has been measured in a conducting polymer.

cond-mat.soft↗

arXiv2025

Leveraging the Bi$_2$O$_3$--Fe$_2$O$_3$ Phase Diagram to Tailor BiFeO$_3$ Structure and Dielectric Response

Advancing the functional performance of bismuth ferrite (BiFeO$_3$) requires precise control over phase stability and microstructure, challenges often complicated by secondary phase formation within the Bi$_2$O$_3$-Fe$_2$O$_3$ system. In this work, we employ a phase-diagram-guided synthesis strategy to clarify the processing-structure-property relationships governing BiFeO$_3$ ceramics. Based on previous reports and our experimental observations, a refined Bi$_2$O$_3$-Fe$_2$O$_3$ phase diagram was constructed identifing the onset of liquid-phase formation near 835$^\circ$C in Bi-rich compositions. Solid-state synthesis using non-stoichiometric precursor ratios (55$\colon$45 and 70$\colon$30 Bi$_2$O$_3$ $\colon$ Fe$_2$O$_3$) reveals that the 55$\colon$45 composition sintered at 775$^\circ$C favours phase-pure rhombohedral $R3c$ BiFeO$_3$ with suppressed sillenite- and mullite-type impurities, lattice contraction, and improved grain uniformity. These structural refinements result in near-Debye dielectric relaxation and a four-orders-of-magnitude enhancement in electrical conductivity relative to lower-temperature or Bi-rich conditions. This work demonstrates the effectiveness of phase-diagram control as a scalable route to tuning dielectric response in BFO-based multiferroics and provides a foundation for processing optimization in complex oxide ceramics.

cond-mat.mtrl-sci↗

arXiv2025

Structural, optical, and dielectric properties of Cr-doped ZnO films via DC magnetron sputtering

Cr-doped ZnO films were fabricated by a new but feasible method, that is, annealing Cr-Zn layers deposited via DC magnetron sputtering in air. Microstructures of the films were investigated using X-ray diffraction, scanning electron microscopy, and atomic force microscopy, intrinsic point defects were identified via photoluminescence spectroscopy, and optical and dielectric properties were analyzed using a UV-vis spectrophotometer and dielectric spectrometer, respectively. It was found that the average grain sizes decrease (56.34 - 39.50 nm), the band gap increases (from 3.18 to 3.23 eV), and the transmittance (at 600 nm) decreases (from 91% to 83%) with increasing Cr. Two activation energies of conduction increase after doping Cr, indicating enhanced temperature stability. At optimal Cr levels, ZnO films exhibit high transmittance and conductivity, exhibiting potential for transparent electrode development. This method can be extended to other doped ZnO films, such as Al-doped ZnO transparent electrodes, to achieve simultaneous improvements in transmittance, conductivity, and stability for flexible and wearable applications.

cond-mat.mtrl-sci↗

arXiv2021

Complex dielectric behaviours in $BiFeO_{3}/Bi_{2}Fe_{4}O_{9}$ ceramics

The complex dielectric permittivity of a sintered ceramic tablet consisting of 70.5 % $BiFeO_{3}$ and 27.7% $Bi_{2}Fe_{4}O_{9}$ was analyzed as a function of temperature from -120 °C to 230 °C. The results reveal a complicated dielectric response with temperature activated relaxation features. They also reveal a ferroelectric phase transition that decayed with repeated heating cycles of the tablet. The source of the behaviour is assigned to relaxation processes happening along the grain boundaries of differing compositions in the tablet. The origin of the phase transition is traced to locally induced strains on grain boundaries because of unit cell size mismatch between $BiFeO_{3}$ and $Bi_{2}Fe_{4}O_{9}$.

cond-mat.mtrl-sci↗