Search for: ferromagnetic-materials
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    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... 

    Magnetoresistance due to domain wall bulging

    , Article Journal of Magnetism and Magnetic Materials ; Volume 322, Issue 16 , August , 2010 , Pages 2401-2404 ; 03048853 (ISSN) Fathi, M. B ; Phirouznia, A ; Sharif University of Technology
    The effect of bulging of domain wall (DW) on the magnetoresistance (MR) is investigated. With taking into account the auto-correlation between the points of the interface, one can formulate the mobility within the relaxation time approximation scheme. The results show that the bulging of DW, evaluated with the commonly accepted magnetic parameters for typical ferromagnetic materials of Co, Fe and Ni, has a countable role into the MR  

    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  

    Spin filtering and spin diode devices in quantum wire systems

    , Article Physica E: Low-Dimensional Systems and Nanostructures ; Volume 27, Issue 3 , 2005 , Pages 325-331 ; 13869477 (ISSN) Shokri, A. A ; Mardaani, M ; Esfarjani, K ; Sharif University of Technology
    Theoretical studies on the spin-dependent transmission and current-voltage characteristic in a mesoscopic system, which consists of two semi-infinite ferromagnetic (FM) leads (as source and drain) separated by a typical periodic quantum dot (QD) are presented. The calculations are based on the tight-binding model and transfer matrix method, and investigate the magnetoresistance (MR) and the spin polarization within the Landauer-Büttiker formalism. The spin-dependent transport behavior can be controlled via a gate voltage and an applied bias in the ballistic regime. The numerical results are shown for a periodic polymer chain with nonmagnetic (NM) and FM leads, and also, with two FM leads.... 

    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.... 

    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... 

    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... 

    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... 

    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... 

    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... 

    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... 

    Approximating the distribution of flaws in magnetic materials using the generalized inverse

    , Article 2011 IEEE International Conference on Imaging Systems and Techniques, IST 2011 - Proceedings, 17 May 2011 through 18 May 2011, Batu Ferringhi ; May , 2011 , Pages 137-141 ; 9781612848969 (ISBN) Ravanbod, H ; Abdollahi Jahdi, S ; Norouzi, E ; Sharif University of Technology
    Non-destructive identification of voids in ferromagnetic materials is of great importance for industrial applications. Magnetic flux leakage technique is used here to examine the defected structure. To this end, an inverse problem should be solved in order to infer the location and depth of internal flaws from the measured leaked magnetic signals. Currently generalized inverse method and singular value decomposition are used for solving such inverse problem. Considering the cracks separation has significant effect on the absolute value of magnetic flux leakage signals, we study different distributions of cracks. In this paper, the magnetic dipole model is proposed to reconstruct the extent... 

    Ferromagnetism and antiferromagnetism coexistence in SrRu 1-xMnxO3: Density functional calculation

    , Article Journal of Solid State Chemistry ; Volume 184, Issue 3 , March , 2011 , Pages 536-545 ; 00224596 (ISSN) Hadipour, H ; Fallahi, S ; Akhavan, M ; Sharif University of Technology
    We have calculated the electronic structure of SrRu1-xMn xO3 using the full potential linearized augmented plane wave method by LSDA and LSDAU. The antiparallel alignment between the Mn and Ru ions are consistent with the competition between ferromagnetism and antiferromagnetism in the low Mn-doped polycrystalline samples. This is in contrast to the appearance of quantum critical point and FM and AFM transitions in the single crystal measurement. Our results show that the discrepancy between different experimental phase diagrams is related to the conditions of sample preparation and also the difference between the degree of magnetic interactions between the Mn and Ru moments. The DOS and the... 

    Investigation of size effects on the physical properties of one-dimensional ising models in nanosystems

    , Article Molecular Physics ; Volume 109, Issue 3 , Feb , 2011 , Pages 385-395 ; 00268976 (ISSN) Taherkhani, F ; Daryaei, E ; Parsafar, G ; Fortunelli, A ; Sharif University of Technology
    Ising models in nanosystems are studied in the presence of a magnetic field. For a one-dimensional (1-D) array of spins interacting via nearest-neighbour and next-nearest-neighbour interactions we calculate the heat capacity, the surface energy, the finite-size free energy and the bulk free energy per site. The heat capacity versus temperature exhibits a common wide peak for systems of any size. A small peak also appears at lower temperatures for small arrays when the ratio of magnetic field spin interaction energy over the nearest-neighbour spin-spin interaction energy, f, is within 0 < F ≤ 0.10 . The peak becomes smaller for longer array and eventually vanishes for long arrays,... 

    Effect of electron correlation in Sr(Ca)Ru1-xCrxO3: Density functional calculation

    , Article Journal of Solid State Chemistry ; Volume 183, Issue 7 , 2010 , Pages 1678-1690 ; 00224596 (ISSN) Hadipour, H ; Akhavan, M ; Sharif University of Technology
    We have investigated the electronic structure of Sr(Ca)Ru1-xCrxO3 using the full potential linearized augmented plane wave method by different approximation such as LSDA and LSDA+U. The LSDA calculation suggest that Cr4+-Ru4+ hybridization is responsible for the high Curie temperature TC in SrRu1-xCrxO3, but it cannot completely describe its physical behavior. Our LSDA+U DOS results for SrRu1-xCrxO3 clearly establishes renormalization of the intra-atomic exchange strength at the Ru sites, arising from the Cr-Ru hybridization. The antiferromagnetic coupling of Cr3+ with Ru4+,5+ lattice increases the screening, which is consistent with the low magnetic moment of the Ru ions. The more distorted... 

    Influence of Fe3O4 nanoparticles in hydroxyapatite scaffolds on proliferation of primary human fibroblast cells

    , Article Journal of Materials Engineering and Performance ; 2016 , Pages 1-9 ; 10599495 (ISSN) Maleki Ghaleh, H ; Aghaie, E ; Nadernezhad, A ; Zargarzadeh, M ; Khakzad, A ; Shakeri, M. S ; Beygi Khosrowshahi, Y ; Siadati, M. H ; Sharif University of Technology
    Springer New York LLC  2016
    Modern techniques for expanding stem cells play a substantial role in tissue engineering: the raw material that facilitates regeneration of damaged tissues and treats diseases. The environmental conditions and bioprocessing methods are the primary determinants of the rate of cultured stem cell proliferation. Bioceramic scaffolds made of calcium phosphate are effective substrates for optimal cell proliferation. The present study investigates the effects of two bioceramic scaffolds on proliferating cells in culture media. One scaffold was made of hydroxyapatite and the other was a mixture of hydroxyapatite and ferromagnetic material (Fe3O4 nanoparticles). Disk-shaped (10 mm × 2 mm) samples of...