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Structural and Electric Transport Properties of Lanthanum Based Manganites and Barium Based Ruthenates
, Ph.D. Dissertation Sharif University of Technology ; Akhavan, Mohammad (Supervisor)
Abstract
The goal of this thesis is to understand the physical properties of lanthanum based manganites and barium based ruthenates. In order to obtain negative colossal magnetoresistance in manganites and fabrication of barium ruthenate in ordinary condition, the effects of variables such as ionic radii, chemical composition, temperature, magnetic field and processing in manganites and ruthenates systems are investigated. In the first part, the effects of potassium doping on structure, metalinsulator transition and magnetoresistance in )La1-yKy)0.7 Ca0.3 MnO3 and)La1-yKy)0.7 Ba0.3 MnO3 manganites systems are studied. Polycrystalline samples of manganites are synthesized by the sol‐gel method. In the...
The Effect of Pressure on the Coexistence of Superconductivity and Magnetism in RuSr2GdCu2O8 and RuSr2Gd1.4Ce0.6Cu2O10-δ
, Ph.D. Dissertation Sharif University of Technology ; Akhavan, Mohammad (Supervisor)
Abstract
The coexistence of long-range magnetic order and superconductivity in the ruthenocuprate families, Ru1212 and Ru1222 has been studied both theoretically and experimentally. Historically these two different phases are incompatible with each other and in the most previous research reported on the coexistence of these phases, there have been observed separated magnetic and superconducting phases. However in the ruthenocuprate families, there is a single phase with both magnetic and superconducting phase which coexist with each other. It has been determined that superconductivity arises in CuO2 planes, and magnetic orders occur in RuO2. From experimental point of view, we have investigated the...
An Investigation into Entanglement in Electrical Transport in a One-dimensional Model Using Transfer Matrix Method
, M.Sc. Thesis Sharif University of Technology ; Rezakhani, Ali (Supervisor) ; Shokri, Ali Asghar (Co-Supervisor)
Abstract
This thesis analyzes the scattering of a propagating electron from a single bound electron .The study demonstrates how the scattering of the propagating electron from the bound electron causes entanglement between two electrons. The study then considers the impact of spin-dependent scattering in the presence of Hartree and exchange potentials. In the first step, only an exchange potential is studied. Transmission coefficients are calculated for spin-flip and non-spin-flip states by solving the Hamiltonian equation in different regions, applying the continuity boundary conditions for the wave function and its derivative in each region, and using the transfer matrix method. Transmission...
Study of Optical and Transport Properties of Sr2RuO4 Superconductor
, M.Sc. Thesis Sharif University of Technology ; Kargarian, Mehdi (Supervisor)
Abstract
The nature of the Cooper pairing in the paradigmatic unconventional superconductor Sr2RuO4 is an outstanding puzzle in condensed matter physics. Despite the tremendous efforts made in the past twenty-seven years, neither the pairing symmetry nor the underlying pairing mechanism in this material has been understood with clear consensus. This is largely due to the lack of a superconducting order that is capable of interpreting in a coherent manner the numerous essential experimental observations. At this stage, it may be desirable to reexamine our existing theoretical descriptions of superconducting Sr2RuO4.This thesis focuses on the experiments that have been carried out so far on Sr2RuO4 and...
Timetable optimization for maximum usage of regenerative energy of braking in electrical railway systems
, Article SPEEDAM 2010 - International Symposium on Power Electronics, Electrical Drives, Automation and Motion, 14 June 2010 through 16 June 2010 ; June , 2010 , Pages 1218-1221 ; 9781424449873 (ISBN) ; Fekri Moghadam, M ; Mokhtari, H ; Sharif University of Technology
2010
Abstract
Research projects in urban transportation systems require proper simulation softwares. Such softwares are the basic requirements of any kind of study in electrical transportation systems. Due to high energy consumption of these systems, studies for its optimization are challenging and necessary. In this paper an optimized timetable of trains? movement is proposed in order to completely utilize the regenerative energy of trains? braking in stations. A sample subway system is simulated and Genetic algorithm is used as an optimization method. The effect of headway and reserve times on the amount of energy consumption is studied and an optimized reserve time set is found for the sample system....
Theoretical study of the electron transport through the cysteine amino acid nanomolecular wire
, Article International Journal of Nanoscience ; Volume 7, Issue 2-3 , 2008 , Pages 95-102 ; 0219581X (ISSN) ; Aghaie, H ; Gholami, M. R ; Sharif University of Technology
World Scientific Publishing Co. Pte Ltd
2008
Abstract
In this paper, we study the electrical transport and Negative Differential Resistance (NDR) in a single molecular conductor consisting of a cysteine sandwiched between two Au(111) electrodes via the Density Functional Theory-based Nonequilibrium Green's Function (DFT-NEGF) method. We show that (surprisingly, despite their apparent simplicity, these Au/cysteine/Au nanowires are shown to be a convenient NDR device) the smallest two-terminal molecular wire can exhibit NDR behavior to date. Experiments with a conventional or novel self-assembled monolayer (SAM) are proposed to test these predictions. The projected density of states (PDOSs) and transmission coefficients T(E) under various...
Effect of Sr/Ba substitution in Gd1-xPrxBaSrCu 3O7-δ
, Article Physica C: Superconductivity and its Applications ; Volume 423, Issue 3-4 , 2005 , Pages 163-174 ; 09214534 (ISSN) ; Akhavan, M ; Sharif University of Technology
2005
Abstract
Tetragonal Gd1-xPrxBaSrCu3O 7-δ (0 ≤ x ≤ 1) polycrystalline samples have been prepared by the standard solid-state reaction, and characterized by XRD and SEM. Resistance measurements and XRD patterns show site mixing between rare earth R and Sr is less than R and Ca. Contrary to Gd1-xPrxBa 2Cu3O7-δ, a hump on the ρ(T) curve is observed at about 80 K. Based on the resistivity measurements, the effect of Pr substitution in the 1113 structure, in comparison with the 123 structure, on the increase of pseudogap temperature is investigated. The normal state resistivity has been analyzed by the two and three dimensional variable range hopping (2D-VRH and 3D-VRH) and Coulomb gap. For the low...
From continuous to quantized charging phenomena in few nanocrystals MOS structures
, Article 11th International Autumn Meeting on Gettering and Defect Engineering in Semiconductor Technology, GADEST 2005, 25 September 2005 through 30 September 2005 ; Volume 108-109 , 2005 , Pages 25-32 ; 10120394 (ISSN); 9783908451136 (ISBN) ; Shalchian, M ; Grisolia, J ; Bonafos, C ; Atarodi, S. M ; Claverie, A ; Pichaud B ; Claverie A ; Alquier D ; Richter H ; Kittler M ; Richter H ; Kittler M ; Sharif University of Technology
Trans Tech Publications Ltd
2005
Abstract
In this paper, we present a study on the contribution of silicon nanocrystals to the electrical transport characteristics of large (100 µ x 100 µm) and small (100 nm x 100 nm) metaloxide- semiconductor (MOS) capacitors at room temperature. A layer of silicon nanocrystals is synthesized within the oxide of these capacitors by ultra-low energy ion implantation and annealing. Several features including negative differential resistance (NDR), sharp current peaks and random telegraph signal (RTS) are demonstrated in the current-voltage and current-time characteristics of these capacitors. These features have been associated to charge storage in silicon nanocrystals and to the resulting Coulomb...
Structural and electrical transport properties of hexagonal 4H BaRu 1-xMnxO3 perovskite
, Article Physica B: Condensed Matter ; Volume 406, Issue 18 , September , 2011 , Pages 3363-3366 ; 09214526 (ISSN) ; Fallahi, S ; Akhavan, M ; Sharif University of Technology
2011
Abstract
In this paper, structural and electrical transport properties of hexagonal, 4H-type, BaRu1-xMnxO3 (x=0-0.3), synthesized by the solid-state reaction method at ambient pressure, have been presented. Electrical transport properties are measured over a temperature range of 10300 K in the magnetic field up to 15 kOe. The low temperature resistivity (10K
First principles study of the I-V characteristics of the alkane-thiols nano-molecular wires
, Article Current Applied Physics ; Volume 9, Issue 2 , 2009 , Pages 367-373 ; 15671739 (ISSN) ; Gholami, M. R ; Darvish Ganji, M ; Taghavi, M. M ; Sharif University of Technology
2009
Abstract
We report a density functional non-equilibrium Green's function study of electrical transport in a single molecular conductor consisting of an ethane-dithiolate (C2H4S2) molecular wire with two sulfur end groups bonded to the Au(1 1 1) electrodes. We show that the current was increased by increasing the external voltage biases. The projected density of states (PDOS) and transmission coefficients T(E) under various external voltage biases are analyzed, and it suggests that the variation of the coupling between the molecule and the electrodes with external bias leads to the increase of the current. Furthermore, the investigation of the transport properties of the pentane-dithiolate (C5H10S2)...
Evolution of quantum electronic features with the size of silicon nanoparticles embedded in a sio2 layer obtained by low energy ion implantation
, Article 11th International Autumn Meeting on Gettering and Defect Engineering in Semiconductor Technology, GADEST 2005, 25 September 2005 through 30 September 2005 ; Volume 108-109 , 2005 , Pages 71-76 ; 10120394 (ISSN); 9783908451136 (ISBN) ; Shalchian, M ; Benassayag, G ; Coffin, H ; Bonafos, C ; Dumas, C ; Atarodi, S. M ; Claverie, A ; Pichaud B ; Claverie A ; Alquier D ; Richter H ; Kittler M ; Richter H ; Kittler M ; Sharif University of Technology
Trans Tech Publications Ltd
2005
Abstract
In this paper, we have studied the evolution of quantum electronic features with the size of silicon nanoparticles embedded in an ultra-thin SiO2 layer. These nanoparticles were synthesized by ultralow energy (1 KeV) ion implantation and annealing. Their size was modified using the effect of annealing under slightly oxidizing ambient (N2+O2). Material characterization techniques including transmission electron microscopy (TEM) Fresnel imaging and spatially resolved electron energy loss spectroscopy (EELS) have been used to evaluate the effects of oxidation on structural characteristics of nanocrystal layer. Electrical transport characteristics have been measured on few (less than two...
Electrical behavior of nano-polycrystalline (La1-yK y)0.7Ba0.3MnO3 manganites
, Article Journal of Magnetism and Magnetic Materials ; Volume 322, Issue 21 , November , 2010 , Pages 3255-3261 ; 03048853 (ISSN) ; Akhavan, M ; Sharif University of Technology
2010
Abstract
We present a study of the structural and electrical behavior of nano-polycrystalline mixed barium and alkali substituted lanthanum-based manganite, (La1-yKy)0.7Ba0.3MnO 3 with y=0.00.3. The samples were synthesized by the polymerization complex solgel method. The powder X-ray diffraction (XRD) data of the samples show a single-phase character with R3c space group. The magnetic and electrical transport properties of the nano-polycrystalline samples have been investigated in the temperature range 50300 K and a magnetic field up to 10 kOe. The metalinsulator transition temperature Tp of all the samples decreased with potassium doping, and also, it increased slightly with the application of...
Preparation and characterization of nano-polycrystalline lanthanum-based manganite (La1 - y Ky)0.7 Ca0.3 MnO3
, Article Physica B: Condensed Matter ; Volume 405, Issue 1 , 2010 , Pages 72-76 ; 09214526 (ISSN) ; Akhavan, M ; Sharif University of Technology
2010
Abstract
A series of nano-polycrystalline alkali metal doped in La-based manganites (La1 - y Ky)0.7 Ca0.3 MnO3 samples (y = 0.0, 0.1, 0.2, and 0.3) were synthesized using the polymerical complex sol-gel method. The structural properties are studied via the X-ray diffraction experiments, and results are refined by the Rietveld method. The electrical transport properties of the polycrystalline samples have been investigated in the temperature range 50-300 K and a magnetic field up to 10 kOe. The metal-insulator transition temperature (Tp) changes with doping due to the difference between the electron configuration and ionic radius of the dopants and manganese trivalent ions. Characteristic grain...