Gassem M. Alzoubi

Bio: Gassem M. Alzoubi is an academic researcher from Hashemite University. The author has contributed to research in topics: Coercivity & Magnetization. The author has an hindex of 5, co-authored 11 publications receiving 192 citations. Previous affiliations of Gassem M. Alzoubi include Michigan State University & Yarmouk University.

Influence of Mn doping on the magnetic and optical properties of ZnO nanocrystalline particles

Abstract: The structural, optical and magnetic properties of Mn doped ZnO nanocrystalline particles, Zn1-xMnxO, with different percentages of Mn content have been studied. XRD and XPS measurements showed that all samples with Mn doping up to x = 0.1 possess typical wurtzite structure and have no other impurity phases. The incorporation of Mn ions into the ZnO lattice was also confirmed by FTIR and UV–Vis. spectroscopy results. Both XRD and SEM results indicated a slight decrease in the grain size with increasing the Mn doping level. The XPS results indicated an increase in the oxygen vacancies concentration with increasing the Mn doping level. The magnetization measurements revealed a weak ferromagnetic behavior at room temperature and a clear ferromagnetic behavior with relatively large coercive fields at low temperature. The ferromagnetic order is improved by increasing the Mn doping. In addition, we observed an increase in the concentration of oxygen vacancies, which is also induced by increasing the Mn doping level. A ferromagnetic coupling of the local moment of Mn dopants through the sp-d exchange interaction and oxygen vacancies, in addition to different magnetic contributions due to different forms of Mn ions that coexist in the Mn doped nanoparticles were presented in order to interpret the observed magnetic behavior. We observed a clear red shift in the direct band gap and an increase in the coercive field and saturation magnetization values with increasing the Mn doping level.

Nonequilibrium tunneling spectroscopy in carbon nanotubes.

Abstract: We report measurements of the nonequilibrium electron energy distribution in carbon nanotubes. Using tunneling spectroscopy via a superconducting probe, we study the shape of the local electron distribution functions, and hence energy relaxation rates, in nanotubes that have bias voltages applied between their ends. At low temperatures, electrons interact weakly in nanotubes of a few microns channel length, independent of end-to-end-conductance values. Surprisingly, the energy relaxation rate can increase substantially when the temperature is raised to only 1.5 K.

Phase Coherence of Conduction Electrons Below the Kondo Temperature

Abstract: We have measured the phase decoherence rate ${\ensuremath{\tau}}_{\ensuremath{\phi}}^{\ensuremath{-}1}$ of conduction electrons in disordered Ag wires implanted with 2 and 10 ppm Fe impurities, by means of the weak-localization magnetoresistance. The Kondo temperature of Fe in Ag, ${T}_{K}\ensuremath{\approx}4\text{ }\text{ }\mathrm{K}$, is in the ideal temperature range to study the progressive screening of the Fe spins as the temperature $T$ falls below ${T}_{K}$. The contribution to ${\ensuremath{\tau}}_{\ensuremath{\phi}}^{\ensuremath{-}1}$ from the Fe impurities is clearly visible over the temperature range 40 mK---10 K. Below ${T}_{K}$, ${\ensuremath{\tau}}_{\ensuremath{\phi}}^{\ensuremath{-}1}$ falls rapidly until $T/{T}_{K}\ensuremath{\approx}0.1$, in agreement with recent theoretical calculations. At lower $T$ ${\ensuremath{\tau}}_{\ensuremath{\phi}}^{\ensuremath{-}1}$ deviates from theory with a flatter $T$-dependence. Understanding this anomalous dephasing for $T/{T}_{K}l0.1$ may require theoretical models with larger spin and number of channels.

Phase coherence of conduction electrons below the Kondo temperature

Abstract: We have measured the phase decoherence rate ${\ensuremath{\tau}}_{\ensuremath{\phi}}^{\ensuremath{-}1}$ of conduction electrons in disordered Ag wires implanted with 2 and 10 ppm Fe impurities, by means of the weak-localization magnetoresistance. The Kondo temperature of Fe in Ag, ${T}_{K}\ensuremath{\approx}4\text{ }\text{ }\mathrm{K}$, is in the ideal temperature range to study the progressive screening of the Fe spins as the temperature $T$ falls below ${T}_{K}$. The contribution to ${\ensuremath{\tau}}_{\ensuremath{\phi}}^{\ensuremath{-}1}$ from the Fe impurities is clearly visible over the temperature range 40 mK---10 K. Below ${T}_{K}$, ${\ensuremath{\tau}}_{\ensuremath{\phi}}^{\ensuremath{-}1}$ falls rapidly until $T/{T}_{K}\ensuremath{\approx}0.1$, in agreement with recent theoretical calculations. At lower $T$ ${\ensuremath{\tau}}_{\ensuremath{\phi}}^{\ensuremath{-}1}$ deviates from theory with a flatter $T$-dependence. Understanding this anomalous dephasing for $T/{T}_{K}l0.1$ may require theoretical models with larger spin and number of channels.

Investigation on X-ray photoelectron spectroscopy, structural and low temperature magnetic properties of Ni-Ti co-substituted M-type strontium hexaferrites prepared by ball milling technique

Abstract: The effect of substituting Fe3+ ions by a combination of divalent Ni2+ and tetravalent Ti4+ in SrM hexaferrites synthesized by mechanical ball-milling technique were reported. Standard SrFe12O19 hexagonal ferrite (P63/mmc) was confirmed by measured XRD patterns. The phase purity was also confirmed by the XPS. The SEM images showed a clear hexagonal-shape particles in the prepared ferrites. The elemental distribution obtained from EDX spectra for SrFe12–2xNixTixO19 (x = 0.2, 0.4, 0.6 and 0.8) was consistent with stoichiometry of the starting powder. X-ray photoelectron spectra confirmed the existence of Fe2+, Fe3+, Ni2+, Ni3+ and Ti4+ ions. The presence of Fe2+ and Ni3+ was correlated with an electron transfer between Fe3+ and Ni2+. By increasing the Ni concentration, we found that some Fe3+ ions are transferred to Fe2+ ions, while some of the Ni2+ ions are transferred to Ni3+ ions. Irreversible ZFC and FC curves were recorded in the 4–300 K temperature range. The isothermal magnetization curves confirmed the ferromagnetic behavior for all synthesized samples. A small variation in the saturation and remnant magnetizations along with a sharp reduction in the coercivity fields with the increase of x were observed in a wide range of temperatures. The broad peak observed in the temperature dependence of the saturation magnetization for x = 0.8 may be referred to the spin reorientation transition. The decrease in the coercivity agrees with the behaviour of the magneto crystalline anisotropy while the first anisotropy constant exhibits a fast decrease above x = 0.6.

Numerical renormalization group method for quantum impurity systems

Abstract: In the early 1970s, Wilson developed the concept of a fully nonperturbative renormalization group transformation. When applied to the Kondo problem, this numerical renormalization group (NRG) method gave for the first time the full crossover from the high-temperature phase of a free spin to the low-temperature phase of a completely screened spin. The NRG method was later generalized to a variety of quantum impurity problems. The purpose of this review is to give a brief introduction to the NRG method, including some guidelines for calculating physical quantities, and to survey the development of the NRG method and its various applications over the last 30 years. These applications include variants of the original Kondo problem such as the non-Fermi-liquid behavior in the two-channel Kondo model, dissipative quantum systems such as the spin-boson model, and lattice systems in the framework of the dynamical mean-field theory.

One-dimensional quantum liquids: Beyond the Luttinger liquid paradigm

Abstract: For many years, the Luttinger liquid theory has served as a useful paradigm for the description of one-dimensional (1D) quantum fluids in the limit of low energies. This theory is based on a linearization of the dispersion relation of the particles constituting the fluid. Recent progress in understanding 1D quantum fluids beyond the low-energy limit is reviewed, where the nonlinearity of the dispersion relation becomes essential. The novel methods which have been developed to tackle such systems combine phenomenology built on the ideas of the Fermi-edge singularity and the Fermi-liquid theory, perturbation theory in the interaction strength, and new ways of treating finite-size properties of integrable models. These methods can be applied to a wide variety of 1D fluids, from 1D spin liquids to electrons in quantum wires to cold atoms confined by 1D traps. Existing results for various dynamic correlation functions are reviewed, in particular, the dynamic structure factor and the spectral function. Moreover, it is shown how a dispersion nonlinearity leads to finite particle lifetimes and its impact on the transport properties of 1D systems at finite temperatures is discussed. The conventional Luttinger liquid theory is a special limit of the new theory, and the relation between the two is explained.

Andreev bound states in supercurrent-carrying carbon nanotubes revealed

Abstract: Although carbon nanotubes are not superconductors they can carry supercurrents injected from superconducting contacts. Analysis of the tunnelling spectra of a nanotube connecting two superconductors reveals the detailed electronic structure of discrete entangled electron–hole states that carry the resulting supercurrent.

Electron liquids and solids in one dimension.

Abstract: Even though bulk metallic systems contain a very large number of strongly interacting electrons, their properties are well described within Landau's Fermi liquid theory of non-interacting quasiparticles. Although many higher-dimensional systems can be successfully understood on the basis of such non-interacting theories, this is not possible for one-dimensional systems. When confined to narrow channels, electron interaction gives rise to such exotic phenomena as spin–charge separation and the emergence of correlated-electron insulators. Such strongly correlated electronic behaviour has recently been seen in experiments on one-dimensional carbon nanotubes and nanowires, and this behaviour challenges the theoretical description of such systems.