Search for: ferromagnetism
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    Kitaev-Ising model and the transition between topological and ferromagnetic order

    , Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 87, Issue 3 , March , 2013 ; 10502947 (ISSN) Karimipour, V ; Memarzadeh, L ; Zarkeshian, P ; Sharif University of Technology
    We study the Kitaev-Ising model, where ferromagnetic Ising interactions are added to the Kitaev model on a lattice. This model has two phases which are characterized by topological and ferromagnetic order. Transitions between these two kinds of order are then studied on a quasi-one-dimensional system, on a ladder, and on a two-dimensional periodic lattice, a torus. By exactly mapping the quasi-one-dimensional case to an anisotropic XY chain we show that the transition occurs at zero λ, where λ is the strength of the ferromagnetic coupling. In the two-dimensional case the model is mapped to a two-dimensional Ising model in transverse field, where it shows a transition at a finite value of λ.... 

    Comparing half-metallic, MOKE, and thermoelectric behavior of the CrTiZ (Z = As, P) half-Heuslers: A DFT study

    , Article Materials Research Express ; Volume 8, Issue 4 , 2021 ; 20531591 (ISSN) Sadeghi, M ; Zelati, A ; Boochani, A ; Arman, A ; Mirzaei, S ; Sharif University of Technology
    IOP Publishing Ltd  2021
    Structural, half-metallic, magneto-optic, and thermoelectric properties of CrTiZ (Z = As, P) half-Heusleres compounds are investigated based on density functional theory. These compounds have mechanical stability in the ferromagnetic state with a high bulk modulus. They are often half-metallic with a large and integer magnetic moment and are very attractive in spintronics, magneto-optics applications. The magnetic moments of CrTiAs and CrTiP were 2.9865 μB and 3.00 μB, respectively, which were attributed to their ferromagnetic phase. Additionally, the positive sign of the phonon branches indicates the dynamic stability of these compounds. Applying both GGA and mBJ approximations, CrTiAs and... 

    Thermal entanglement of spins in mean-field clusters

    , Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 73, Issue 6 , 2006 ; 10502947 (ISSN) Asoudeh, M ; Karimipour, V ; Sharif University of Technology
    We determine thermal entanglement in mean-field clusters of N spin one-half particles interacting via the anisotropic Heisenberg interaction, with and without external magnetic field. For the xxx cluster in the absence of magnetic field we prove that only the N=2 ferromagnetic cluster shows entanglement. An external magnetic field B can only entangle xxx antiferromagnetic clusters in certain regions of the B-T plane. On the other hand, the xxz clusters of size N>2 are entangled only when the interaction is ferromagnetic. Detailed dependence of the entanglement on various parameters is investigated in each case. © 2006 The American Physical Society  

    Investigation of switching time and pressure head effects on hydro magnetic micro-pump and flow controller

    , Article 2008 Proceedings of the ASME Fluids Engineering Division Summer Conference, FEDSM 2008, 10 August 2008 through 14 August 2008, Jacksonville, FL ; Volume 2 , 2009 , Pages 463-470 ; 9780791848418 (ISBN) Esmaily Moghadam, M ; Shafii, M. B ; Fluids Engineering Division, ASME ; Sharif University of Technology
    The significant importance of micro-scaled devices in medicine, lab-on-a-chip, and etc resulted in a vast variety of researches. The idea behind the novel hydro magnetic micro-pump and flow controller is that ferromagnetic particles, mixed and dispersed in a carrier fluid, can be accumulated and retained at specific sites to form pistons in a micro-tube using some external magnetic field sources along the micro-tube. This external magnetic field is related to some solenoids, which are turned on and off alternatively. Depending upon dragging speed of these pistons, which itself is a function of switching time, this device can be used to either increase (pumping) or decrease (valving) the flow... 

    Spin ladder with anisotropic ferromagnetic legs in a transverse magnetic field

    , Article Journal of Physics Condensed Matter ; Volume 19, Issue 7 , 2007 ; 09538984 (ISSN) Japaridze, G. I ; Langari, A ; Mahdavifar, S ; Sharif University of Technology
    We have studied the ground-state phase diagram of a two-leg spin ladder with anisotropic ferromagnetic leg couplings under the influence of a symmetry-breaking transverse magnetic field by the exact diagonalization technique. In the case of antiferromagnetic coupling between legs we identified two phase transitions in the plane of magnetic field versus interchain coupling strength. The first corresponds to the transition from the gapped rung-singlet phase to the gapped stripe-ferromagnetic phase. The second represents the transition from the gapped stripe-ferromagnetic phase into the fully polarized ferromagnetic phase. © IOP Publishing Ltd  

    Mutual Effects between Earth's Magnetic Field and Marine Vehicles and their Modeling & Demagnetization

    , M.Sc. Thesis Sharif University of Technology Zareei, Abdulkhaled (Author) ; Sayyaadi, Hassan (Supervisor) ; Mehdigholi, Hamid (Supervisor)
    In the construction of naval vessels and some merchant ships, stealth to avoid detection is an important design feature. With recent advances in electromagnetic sensor technology, the war time threat to shipping posed by electromagnetically triggered mines is becoming more significant and consequently the need to understand, predict and reduce the electromagnetic signature of ships is growing.
    The objective of this theoretical-practical work is to derive solutions to static ferromagnetic problems that include current-carrying coils, uniform inducing fields, and linear and homogeneous ferromagnetic bodies. The solutions obtained with the open source FEMM 4.2 software, is validated by... 

    Self-biased low loss conductor featured with skin effect suppression for high quality RF passives

    , Article IEEE Transactions on Magnetics ; Volume 48, Issue 11 , 2012 , Pages 4139-4142 ; 00189464 (ISSN) Iramnaaz, I ; Schellevis, H ; Rejaei, B ; Fitch, R ; Zhuang, Y ; Sharif University of Technology
    IEEE  2012
    We present experimental data for artificial metaconductors exhibiting skin effect suppression at microwave frequencies. The metaconductor consists of a stack comprising twelve periods of alternating ferromagnetic (Permalloy) and normal metal (Cu) layers. Near the effective antiferromagnetic resonant frequency the average in-plane magnetic permeability of the stack approaches zero, leading to an increase in the skin depth. Compared to a Cu-based device, up to 70% loss reduction has been achieved by a metaconductor based coplanar wave guide at ∼ 10 GHz without changing the propagation wavelength. Moreover, unlike conventional magnetic devices, no external magnetic bias is required due to the... 

    High-quality integrated inductors based on multilayered meta-conductors

    , Article IEEE Microwave and Wireless Components Letters ; Volume 22, Issue 7 , 2012 , Pages 345-347 ; 15311309 (ISSN) Iramnaaz, I ; Schellevis, H ; Rejaei, B ; Fitch, R ; Zhuang, Y ; Sharif University of Technology
    We demonstrate high-quality integrated inductors built from a multilayer of alternating copper and ferromagnetic films. The multilayer acts as a meta-conductor whose effective permeability becomes nearly zero at its ferromagnetic anti-resonance frequency. This leads to a suppression of the skin effect and a significant increase in the quality factor of the device. Experiments show an up to 86% increase in quality factor compared to conventional copper-based spiral inductors at high frequencies  

    Effect of Ca substitution on crystal structure and superconducting properties of ferromagnetic superconductor RuSr 2-xCa xGd 1.4Ce 0.6Cu 2O 10 -δ

    , Article Journal of Magnetism and Magnetic Materials ; Volume 324, Issue 6 , 2012 , Pages 949-954 ; 03048853 (ISSN) Fallahi, S ; Mazaheri, M ; Nikseresht, N ; Rønnow, H. M ; Akhavan, M ; Sharif University of Technology
    We have investigated the effect of Ca substitution for Sr site on structural, magnetic and superconducting properties of RuSr2 -x CaxGd1.4Ce0.6Cu2O10 -δ system. In this system, the magnetic coupling of RuO 2 and CuO 2 plays an important role in magnetic and superconducting states. X-ray diffraction analysis shows that all samples are single phase and the lattice parameters decrease continuously by increasing Ca content. The onset superconducting transition temperature is found to decrease with Ca substitution. As Ca content increases, rotation of the RuO 6 octahedron increases and RuO(1)Ru angle decreases. These variations strengthen the magnetic moments in the RuO 2 planes. The enhancement... 

    Memory effects in spin-chain channels for information transmission

    , Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 77, Issue 5 , 2008 ; 10502947 (ISSN) Bayat, A ; Burgarth, D ; Mancini, S ; Bose, S ; Sharif University of Technology
    We investigate the multiple use of a ferromagnetic spin chain for quantum and classical communications without resetting. We find that the memory of the state transmitted during the first use makes the spin chain a qualitatively different quantum channel during the second transmission, for which we find the relevant Kraus operators. We propose a parameter to quantify the amount of memory in the channel and find that it influences the quality of the channel, as reflected through fidelity and entanglement transmissible during the second use. For certain evolution times, the memory allows the channel to exceed the memoryless classical capacity (achieved by separable inputs) and in some cases it... 

    Thermal entanglement of spins in an inhomogeneous magnetic field

    , Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 71, Issue 2 , 2005 ; 10502947 (ISSN) Asoudeh, M ; Karimipour, V ; Sharif University of Technology
    American Physical Society  2005
    We study the effect of inhomogeneities in the magnetic field on the thermal entanglement of a two-spin system. We show that in the ferromagnetic case a very small inhomogeneity is capable of producing large values of thermal entanglement. This shows that the absence of entanglement in the ferromagnetic Heisenberg system is highly unstable against inhomogeneity of magnetic fields, which is inevitably present in any solid state realization of qubits. © 2005 The American Physical Society  

    Temperature and voltage dependence of magnetic barrier junctions with a nonmagnetic spacer

    , Article European Physical Journal B ; Volume 42, Issue 2 , 2004 , Pages 187-191 ; 14346028 (ISSN) Shokri, A. A ; Saffarzadeh, A ; Sharif University of Technology
    The temperature and voltage dependence of spin transport is theoretically investigated in a new type of magnetic tunnel junction, which consists of two ferromagnetic outer electrodes separated by a ferromagnetic barrier and a nonmagnetic (NM) metallic spacer. The effect of spin fluctuation in magnetic barrier, which plays an important role at finite temperature, is included by taking the mean-field approximation. It is found that, the tunnel magnetoresistance (TMR) and the electron-spin polarization depend strongly on the temperature and the applied voltage. The TMR and spin polarization at different temperatures show an oscillatory behavior as a function of the NM spacer thickness. Also,... 

    The effects of a magnetic barrier and a nonmagnetic spacer in tunnel structures

    , Article Journal of Physics Condensed Matter ; Volume 16, Issue 25 , 2004 , Pages 4455-4463 ; 09538984 (ISSN) Shokri, A. A ; Saffarzadeh, A ; Sharif University of Technology
    The spin-polarized transport is investigated in a new type of magnetic tunnel junction which consists of two ferromagnetic electrodes separated by a magnetic barrier and a nonmagnetic metallic spacer. Based on the transfer matrix method and the nearly-free-electron approximation the dependence of the tunnel magnetoresistance (TMR) and electron-spin polarization on the nonmagnetic layer thickness and the applied bias voltage are studied theoretically. The TMR and spin polarization show an oscillatory behaviour as a function of the spacer thickness and the bias voltage. The oscillations originate from the quantum well states in the spacer, while the existence of the magnetic barrier gives rise... 

    Optimized design and implementation of low-cost, sensitive and versatile vibrating sample magnetometer

    , Article ICEE 2012 - 20th Iranian Conference on Electrical Engineering, 15 May 2012 through 17 May 2012 ; May , 2012 , Pages 202-205 ; 9781467311489 (ISBN) Hosseini, N ; Khiabani, S ; Sarreshtedari, F ; Fardmanesh, M ; Sharif University of Technology
    Geometry of different electromagnetic parts of Vibrating Sample Magnetometer (VSM) is a major factor of VSM output voltage. In this paper design, geometry optimization and implementation of a sensitive, versatile and relatively inexpensive VSM system has been described. Considering all effective geometrical parameters in the system output voltage, the induced voltage in the pick-up coils has been obtained analytically and the geometry of the pick-up coils has been optimized for maximum output induced voltage. Two opposite series of pick-up coils, piezoelectric based vibration system and required electronic circuits have been designed and the VSM system has been implemented. The implemented... 

    Enhancement of pool boiling heat transfer using ferromagnetic beads in a variable magnetic field

    , Article Applied Thermal Engineering ; Volume 164 , 2020 Rahmati, P ; Ebrahimi Dehshali, M ; Hakkaki Fard, A ; Sharif University of Technology
    Elsevier Ltd  2020
    The pool boiling is one of the heat transfer mechanisms used in cooling systems. Using an external force to improve the efficiency of thermo-fluid systems is among the most effective approaches, and also highly applicable in enhancing heat transfer. In this study, the pool boiling of water, as the working fluid, in the presence of a variable magnetic field, is studied. To this end, ferromagnetic beads were placed on the boiling surface, and the effect of their movements due to a variable magnetic field was observed and measured. The number of beads was selected such that they would cover 1/3, 1/2 and 2/3 of the surface in different cases and the magnetic field was controlled by altering... 

    Effect of Correlation in SrRu03 Metal Sand LiF Insulators

    , Ph.D. Dissertation Sharif University of Technology Hadipour Siahmazgi, Hanif (Author) ; Akhavan, Mohammad (Supervisor)
    There is no satisfactory agreement between theory and experiment in the Hartree-Fock (HF) and density functional theory (DFT) calculation for metals, semiconductors and metals. It is clear that this discrepancy is attributed to the neglecting of correlation. For example, experimentally
    LiF have the largest band gap about 13.6 eV among the alkali halides and show an exciton peak at 12.6 eV . Brener have obtained a value of 22.9 eV for LiF band gap in the HF approximation. DFT has been very successful tool in calculating the ground-state properties of materials. As
    we expect, the band gap in LiF are underestimated in the local density approximation (LDA) calculation (about 8.3 eV) .... 

    GMR in multilayered nanowires electrodeposited in track-etched polyester and polycarbonate membranes

    , Article Journal of Magnetism and Magnetic Materials ; Volume 308, Issue 1 , 2007 , Pages 35-39 ; 03048853 (ISSN) Nasirpouri, F ; Southern, P ; Ghorbani, M ; Iraji zad, A ; Schwarzacher, W ; Sharif University of Technology
    Commercially available track-etched polyester membranes were used as templates to electrodeposit Co-Ni-Cu/Cu multilayered nanowires, giving room-temperature current perpendicular to plane (CPP) giant magnetoresistance (GMR) values of up to ∼12%. In contrast to similar nanowires electrodeposited in track-etched polycarbonate membranes, the GMR obtained in multilayered nanowires electrodeposited in the polyester membranes increased with decreasing Cu-layer thickness tCu, for tCu in the 2-7 nm range, indicating a lack of ferromagnetic coupling through pinholes, etc. Transmission electron micrographs showed clear evidence for smooth, parallel layer interfaces in the nanowires. © 2006 Elsevier... 

    Thermal entanglement of spins in the Heisenberg model at low temperatures

    , Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 70, Issue 5 A , 2004 , Pages 052307-1-052307-5 ; 10502947 (ISSN) Asoudeh, M ; Karimipour, V ; Sharif University of Technology
    The entanglement between two spins in the ferromagnetic Heisenberg chain at low temperatures was calculated. It was shown that if a magnetic field is applied to a ferromagnetic Heisenberg chain, then pairwise entanglement develops between spins at arbitrary given states. It was also shown that the entanglement profile is a Gaussian with a characteristic length depending on the temperature and the coupling between spins only when the ground state and the one-particle states are populated. The magnetic field was shown to affect only the amplitude of the profile and not its characteristic length  

    Reduced master equation for modeling of ferromagnetic single-electron transistor

    , Article Applied Mechanics and Materials, 29 July 2011 through 31 July 2011, Bangkok ; Volume 110-116 , July , 2012 , Pages 3103-3110 ; 16609336 (ISSN) ; 9783037852620 (ISBN) Asgari, S ; Faez, R ; Sharif University of Technology
    In this paper, the reduced master equation which is a fast simulation method of spin dependent transport in ferromagnetic single electron transistors is presented, for first time. This simulation method follows steady state master equation in which all charge states of the system are considered, whereas charge states are decreased in reduced master equation. This method is based on two degrees of electron freedom which are charge and spin. This is applied in the condition that orthodox tunneling theory is applicable to calculate the tunneling rate of electrons through barriers. The comparison between the I-V characteristics of a ferromagnetic single-electron transistor by following the... 

    Modeling and parametric studies of magnetic shape memory alloy–based energy harvester

    , Article Journal of Intelligent Material Systems and Structures ; Volume 29, Issue 4 , 2018 , Pages 563-573 ; 1045389X (ISSN) Sayyaadi, H ; Rostami Najafabadi, H ; Askari Farsangi, M. A ; Sharif University of Technology
    SAGE Publications Ltd  2018
    This article presents a model to simulate the behavior of a magnetic shape memory alloy while harvesting vibratory energy. In this type of energy harvester, magnetic shape memory alloy element is placed in the air gap of a ferromagnetic core which conducts the magnetic flux. Two apparent coils are wound around a ferromagnetic core: one to produce bias magnetic field by passing a rectified electric current and the other to serve as an energy pickup coil. Applying compressive time-variant strain field to magnetic shape memory alloy element changes its dimensions and magnetic properties as well. Presence of the bias magnetic field returns magnetic shape memory alloy element to its initial state...