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Full-Text Articles in Engineering
Ferroelectric Switch For Spin Injection, Mikhail Ye. Zhuravlev, Sitaram Jaswal, Evgeny Y. Tsymbal, Renat F. Sabirianov
Ferroelectric Switch For Spin Injection, Mikhail Ye. Zhuravlev, Sitaram Jaswal, Evgeny Y. Tsymbal, Renat F. Sabirianov
Materials Research Science and Engineering Center: Faculty Publications
A method for the switching of the spin polarization of the electric current injected into a semiconductor is proposed, based on injecting spins from a diluted magnetic semiconductor through a ferroelectric tunnel barrier. We show that the reversal of the electric polarization of the ferroelectric results in a sizable change in the spin polarization of the injected current, thereby providing a two-state electrical control of this spintronic device. We also predict a possibility of switching of tunneling magnetoresistance in magnetic tunnel junctions with a ferroelectric barrier and coexistence of tunneling magnetoresistance and giant electroresistance effects in these multiferroic tunnel junctions.
Negative Spin Polarization And Large Tunneling Magnetoresistance In Epitaxial Co|Srtio3|Co Magnetic Tunnel Junctions, Julian P. Velev, Kirill D. Belashchenko, Derek A. Stewart, Mark Van Schilfgaarde, Sitaram Jaswal, Evgeny Y. Tsymbal
Negative Spin Polarization And Large Tunneling Magnetoresistance In Epitaxial Co|Srtio3|Co Magnetic Tunnel Junctions, Julian P. Velev, Kirill D. Belashchenko, Derek A. Stewart, Mark Van Schilfgaarde, Sitaram Jaswal, Evgeny Y. Tsymbal
Materials Research Science and Engineering Center: Faculty Publications
We perform an ab initio study of spin-polarized tunneling in epitaxial Co|SrTiO3|Co magnetic tunnel junctions with bcc Co(001) electrodes. We predict a large tunneling magnetoresistance in these junctions, originating from a mismatch in the majority- and minority-spin bands both in bulk bcc Co and at the Co|SrTiO3 interface. The intricate complex band structure of SrTiO3 enables efficient tunneling of the minority d electrons which causes the spin polarization of the Co|SrTiO3 interface to be negative in agreement with experimental data. Our results indicate that epitaxial Co|SrTiO3|Co magnetic tunnel junctions with bcc Co(001) electrodes …
Effect Of Interface States On Spin-Dependent Tunneling In Fe/Mgo/Fe Tunnel Junctions, Kirill D. Belashchenko, Julian P. Velev, Evgeny Y. Tsymbal
Effect Of Interface States On Spin-Dependent Tunneling In Fe/Mgo/Fe Tunnel Junctions, Kirill D. Belashchenko, Julian P. Velev, Evgeny Y. Tsymbal
Materials Research Science and Engineering Center: Faculty Publications
The electronic structure and spin-dependent tunneling in epitaxial Fe/MgO/Fe(001) tunnel junctions are studied using first-principles calculations. For small MgO barrier thickness the minority-spin resonant bands at the two interfaces make a significant contribution to the tunneling conductance for the antiparallel magnetization, whereas these bands are, in practice, mismatched by disorder and/or small applied bias for the parallel magnetization. This explains the experimentally observed decrease in tunneling magnetoresistance (TMR) for thin MgO barriers. We predict that a monolayer of Ag epitaxially deposited at the interface between Fe and MgO suppresses tunneling through the interface band and may thus be used to …
Domain-Wall Magnetoresistance Of Co Nanowires, Renat F. Sabiryanov, Ashok K. Solanki, John D. Burton, Sitaram Jaswal, Evgeny Y. Tsymbal
Domain-Wall Magnetoresistance Of Co Nanowires, Renat F. Sabiryanov, Ashok K. Solanki, John D. Burton, Sitaram Jaswal, Evgeny Y. Tsymbal
Materials Research Science and Engineering Center: Faculty Publications
Using density functional theory implemented within a tight-binding linear muffin-tin orbital method we perform calculations of electronic, magnetic, and transport properties of ferromagnetic free-standing fcc Co wires with diameters up to 1.5 nm. We show that finite-size effects play an important role in these nanowires resulting in oscillatory behavior of electronic charge and the magnetization as a function of the wire thickness, and a nonmonotonic behavior of spin-dependent quantized conductance. We calculate the magnetoresistance (MR) of a domain wall (DW) modeled by a spin-spiral region of finite width sandwiched between two semi-infinite Co wire leads. We find that the DW …
Giant Electroresistance In Ferroelectric Tunnel Junctions, Mikhail Ye Zhuravlev, Renat F. Sabirianov, Sitaram Jaswal, Evgeny Y. Tsymbal
Giant Electroresistance In Ferroelectric Tunnel Junctions, Mikhail Ye Zhuravlev, Renat F. Sabirianov, Sitaram Jaswal, Evgeny Y. Tsymbal
Materials Research Science and Engineering Center: Faculty Publications
The interplay between the electron transport in metal-ferroelectric-metal junctions with ultrathin ferroelectric barriers and the polarization state of a barrier is investigated. Using a model which takes into account screening of polarization charges in metallic electrodes and direct quantum tunneling across a ferroelectric barrier, we calculate the change in the tunneling conductance associated with the polarization switching. We find the conductance change of a few orders of magnitude for metallic electrodes with significantly different screening lengths. This giant electroresistance effect is the consequence of a different potential profile seen by transport electrons for the two opposite polarization orientations.
Strain Induced Half-Metal To Semiconductor Transition In Gdn, Chun-Gang Duan, Renat F. Sabirianov, Jianjun Liu, Wai-Ning Mei, Peter A. Dowben, J. R. Hardy
Strain Induced Half-Metal To Semiconductor Transition In Gdn, Chun-Gang Duan, Renat F. Sabirianov, Jianjun Liu, Wai-Ning Mei, Peter A. Dowben, J. R. Hardy
Materials Research Science and Engineering Center: Faculty Publications
We investigate the electronic structure and magnetic properties of GdN as a function of unit cell volume. Based on the first-principles calculations of GdN, we observe that there is a transformation in the conduction properties associated with the volume increase: first from half-metallic to semimetallic, then ultimately to semiconducting. We show that applying stress can alter the carrier concentration as well as mobility of the holes and electrons in the majority spin channel. In addition, we found that the exchange parameters depend strongly on lattice constant, thus the Curie temperature of this system can be enhanced by applying stress or …
Positive Spin Polarization In Co/Alo3 /Co Tunnel Junctions Driven By Oxygen Adsorption, Kirill D. Belashchenko, Evgeny Y. Tsymbal, Ivan I. Oleynik, Mark Van Schilfgaarde
Positive Spin Polarization In Co/Alo3 /Co Tunnel Junctions Driven By Oxygen Adsorption, Kirill D. Belashchenko, Evgeny Y. Tsymbal, Ivan I. Oleynik, Mark Van Schilfgaarde
Materials Research Science and Engineering Center: Faculty Publications
Using a first-principles Green's function technique, we study spin-dependent tunneling in two model realizations of (111) fcc Co/Al3/Co tunnel junctions assuming O-terminated crystalline epitaxy in the corundum structure. For the first model, which includes 3 O atoms at the interface, the tunneling current is polarized negatively, just as for the clean Co surface. The second model contains additional oxygen atoms inside large pores at each interface. Located at the three-fold hollow adsorption sites, these O atoms bind very strongly to Co. This bonding creates an interface band in the majority-spin channel which strongly enhances the tunneling current in this channel. …
Role Of Interface Bonding In Spin-Dependent Tunneling (Invited), Evgeny Y. Tsymbal, Kirill D. Belashchenko
Role Of Interface Bonding In Spin-Dependent Tunneling (Invited), Evgeny Y. Tsymbal, Kirill D. Belashchenko
Materials Research Science and Engineering Center: Faculty Publications
Measured positive values of the spin polarization of the tunneling current from 3d ferromagnetic metals are commonly explained by the dominant s-electron contribution based on symmetry considerations for bulk materials, ignoring the influence of the interfaces. In this work, three different models are considered which suggest that the spin polarization is primarily determined by the electronic and atomic structures of the ferromagnet/insulator interfaces rather than by the bulk properties. A simple tight-binding model demonstrates that the existence of interface states and their contribution to the tunneling current depend on the degree of hybridization between the orbitals on metal …
A Symmetric Green Function For The Non-Collinear Magnetic Multilayer, Mikhail Ye Zhuravlev, John D. Burton, A. V. Vedyayev, Evgeny Y. Tsymbal
A Symmetric Green Function For The Non-Collinear Magnetic Multilayer, Mikhail Ye Zhuravlev, John D. Burton, A. V. Vedyayev, Evgeny Y. Tsymbal
Materials Research Science and Engineering Center: Faculty Publications
Symmetry properties of the Green function in magnetic multilayers with noncollinear magnetization of the layers are investigated on the basis of the transfer matrix method. The Green function symmetric with respect to permutation of its arguments is constructed. It is shown how the boundary conditions can be imposed on this Green function.
We have proposed a constructive way to build a symmetric one-electron GF for the magnetic multilayer with magnetization in the plane of the layers. To build this GF we solved the following problems: finding the solution of the systems of differential equations of general form; matching the solutions …
Ballistic Anisotropic Magnetoresistance, Julian P. Velev, Renat F. Sabirianov, Sitaram Jaswal, Evgeny Y. Tsymbal
Ballistic Anisotropic Magnetoresistance, Julian P. Velev, Renat F. Sabirianov, Sitaram Jaswal, Evgeny Y. Tsymbal
Materials Research Science and Engineering Center: Faculty Publications
Electronic transport in ferromagnetic ballistic conductors is predicted to exhibit ballistic anisotropic magnetoresistance—a change in the ballistic conductance with the direction of magnetization. This phenomenon originates from the effect of the spin-orbit interaction on the electronic band structure which leads to a change in the number of bands crossing the Fermi energy when the magnetization direction changes. We illustrate the significance of this phenomenon by performing ab initio calculations of the ballistic conductance in ferromagnetic Ni and Fe nanowires which display a sizable ballistic anisotropic magnetoresistance when magnetization changes direction from parallel to perpendicular to the wire axis.
Texture Formation In Fept Thin Films Via Thermal Stress Management, P. Rasmussen, X. Rui, Jeffrey E. Shield
Texture Formation In Fept Thin Films Via Thermal Stress Management, P. Rasmussen, X. Rui, Jeffrey E. Shield
Materials Research Science and Engineering Center: Faculty Publications
The transformation variant of the fcc to fct transformation in FePt thin films was tailored by controlling the stresses in the thin films, thereby allowing selection of in- or out-of-plane c-axis orientation. FePt thin films were deposited at ambient temperature on several substrates with differing coefficients of thermal expansion relative to the FePt, which generated thermal stresses during the ordering heat treatment. X-ray diffraction analysis revealed preferential out-of-plane c-axis orientation for FePt films deposited on substrates with a similar coefficients of thermal expansion, and random orientation for FePt films deposited on substrates with a very low coefficient of …
High-Anisotropy Nanocluster Films For High-Density Perpendicular Recording, David J. Sellmyer, Minglang Yan, Yinfan Xu, Ralph Skomski
High-Anisotropy Nanocluster Films For High-Density Perpendicular Recording, David J. Sellmyer, Minglang Yan, Yinfan Xu, Ralph Skomski
Materials Research Science and Engineering Center: Faculty Publications
This paper reports results on the synthesis and magnetic properties of L10:X nanocomposite films, where L10 = FePt, CoPt, and X = C, Ag, etc. Two fabrication methods are discussed: nonepitaxial growth of oriented perpendicular media, and monodispersed nanoparticle-assembled films grown with a gas-aggregation source. The magnetic properties are controllable through variations in the nanocluster properties and nanostructure. The films show promise for development as recording media at extremely high areal densities.
Impurity-Assisted Interlayer Exchange Coupling Across A Tunnel Barrier, Mikhail Ye Zhuravlev, Evgeny Y. Tsymbal, A. V. Vedyayev
Impurity-Assisted Interlayer Exchange Coupling Across A Tunnel Barrier, Mikhail Ye Zhuravlev, Evgeny Y. Tsymbal, A. V. Vedyayev
Materials Research Science and Engineering Center: Faculty Publications
Localized impurity or defect states in the insulating barrier layer separating two ferromagnetic films affect dramatically the interlayer exchange coupling (IEC), making it significantly stronger compared to perfect barriers. We demonstrate that the impurity-assisted IEC becomes antiferromagnetic if the energy of the impurity states matches the Fermi energy and that the coupling strength decreases with temperature. These results explain available experimental data on the IEC across tunnel barriers.
The Stability And Oxidation Resistance Of Iron- And Cobalt-Based Magnetic Nanoparticle Fluids Fabricated By Inert-Gas Condensation, Nguyen H. Hai, Raymond Lemoine, Shaina Remboldt, Michelle A. Strand, Steve Wignall, Jeffrey E. Shield, Diandra Leslie-Pelecky
The Stability And Oxidation Resistance Of Iron- And Cobalt-Based Magnetic Nanoparticle Fluids Fabricated By Inert-Gas Condensation, Nguyen H. Hai, Raymond Lemoine, Shaina Remboldt, Michelle A. Strand, Steve Wignall, Jeffrey E. Shield, Diandra Leslie-Pelecky
Materials Research Science and Engineering Center: Faculty Publications
Magnetic nanoparticle fluids have numerous biomedical applications, including magnetic imaging, drug delivery, and hyperthermia treatment for cancer. Ideal magnetic nanoparticle fluids have well-separated, biocompatible nanoparticles with a small size distribution that form a stable colloid. We have combined inert-gas condensation, which produces nanoparticles with low polydispersity, with deposition directly into a surfactant-laden fluid to prevent agglomeration. Iron, cobalt, and iron-nitride nanoparticle fluids fabricated using inert-gas condensation have with mean particle sizes from 5-50 nm and remain stable over long periods of time. Iron and cobalt nanoparticles oxidize on exposure to air, with oxidation rates dependent on surfactant type and concentration. …
Multiscale Phenomena In Bruggeman Composites, Ralph Skomski, Jiangyu Li, Jian Zhou, David J. Sellmyer
Multiscale Phenomena In Bruggeman Composites, Ralph Skomski, Jiangyu Li, Jian Zhou, David J. Sellmyer
Materials Research Science and Engineering Center: Faculty Publications
Mechanical, magnetic, and transport properties of arbitrary inhomogeneous composites are investigated by a Bruggeman-type mean-field approach. The theory yields materials parameters as functions of the volume fractions, geometries, and materials constants of the phases. Each system is described by a single response parameter g, which is equal to the percolation threshold of the composite. For macroscopic systems, the approach yields very simple expressions, but nanoscale and multiferroic effects yield relatively complicated corrections to g. In the respective cases, the parameter g depends on the length scale of the composite and has the character of a combination of magnetic, electric, and …
Nanomagnetic Structures: Fabrication And Interactions, David J. Sellmyer, Y. C. Sui, Yinfan Xu, M. L. Yan, Kory D. Sorge, Ralph Skomski
Nanomagnetic Structures: Fabrication And Interactions, David J. Sellmyer, Y. C. Sui, Yinfan Xu, M. L. Yan, Kory D. Sorge, Ralph Skomski
Materials Research Science and Engineering Center: Faculty Publications
Magnetic nanostructures with desirable properties such as monodispersed size and crystallographic texturing can be fabricated by a number of synthetic techniques. In this paper, we discuss methods for creating nanoclusters with fine control of individual properties and their interactions, as well as a promising chemical technique that provides control of several properties simultaneously. Current and potential applications also will be addressed.
Mercury And C2B10 Icosahedra Interaction, Carolina C. Ilie, Petru Lunca-Popa, Jiandi Zhang, Bernard Doudin, Peter A. Dowben
Mercury And C2B10 Icosahedra Interaction, Carolina C. Ilie, Petru Lunca-Popa, Jiandi Zhang, Bernard Doudin, Peter A. Dowben
Materials Research Science and Engineering Center: Faculty Publications
We contrast the interaction of mercury with adsorbed orthocarborane films and semiconducting (dehydrogenated) boron carbide. Photoemission spectra reveal small shifts in orthocarborane (C2B10H12) molecular orbital binding energies as well as the shift in mercury 5d5/2shallow core level binding energies, suggesting only small interaction between mercury and the molecular film. Mercury does, however, interact with decomposed orthocarboranes i.e. semiconducting boron carbide.
Research Experiences For Teachers In Materials Science: A Case Study, Michelle A. Strand, Steve Wignall, Diandra Leslie-Pelecky
Research Experiences For Teachers In Materials Science: A Case Study, Michelle A. Strand, Steve Wignall, Diandra Leslie-Pelecky
Materials Research Science and Engineering Center: Faculty Publications
The National Science Education Standards encourage teachers to become involved in research as ‘representatives of science in the classroom’. The Research Experiences for Teachers program affiliated with the Materials Research Science and Engineering Center at the University of Nebraska involves teachers in research on nanoscale magnetic and electronic structures over a summer. Two teachers and a sponsoring researcher share their experiences and what they believe are necessary elements for successful RET experiences.