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Articles 241 - 270 of 307

Full-Text Articles in Materials Science and Engineering

A Measurement Of Electron-Wall Interactions Using Transmission Diffraction From Nanofabricated Gratings, Brett E. Barwick, Glen Gronniger, Lu Yuan, Sy-Hwang Liou, Herman Batelaan Jan 2006

A Measurement Of Electron-Wall Interactions Using Transmission Diffraction From Nanofabricated Gratings, Brett E. Barwick, Glen Gronniger, Lu Yuan, Sy-Hwang Liou, Herman Batelaan

Materials Research Science and Engineering Center: Faculty Publications

Electron diffraction from metal coated freestanding nanofabricated gratings is presented, with a quantitative path integral analysis of the electron-grating interactions. Electron diffraction out to the 20th order was observed indicating the high quality of our nanofabricated gratings. The electron beam is collimated to its diffraction limit with ion-milled material slits. Our path integral analysis is first tested against single slit electron diffraction, and then further expanded with the same theoretical approach to describe grating diffraction. Rotation of the grating with respect to the incident electron beam varies the effective distance between the electron and grating bars. This allows the measurement …

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Nanobiomagnetics, Diandra Leslie-Pelecky, V. Labhasetwar, R. H. Kraus Jr. Jan 2006

Nanobiomagnetics, Diandra Leslie-Pelecky, V. Labhasetwar, R. H. Kraus Jr.

Materials Research Science and Engineering Center: Faculty Publications

The application of nanomagnetic materials to biological systems has produced significant advances in research, diagnosis, and treatment of numerous pathologies. This chapter summarizes the major applications of magnetic materials: magnetic targeting, drug and gene delivery, magnetic separation, the use of magnetic beads in manipulating single molecules, as contrast agents in magnetic resonance imaging, and for hyperthermia. Biocompatibility requirements for magnetic materials used in these applications are reviewed.

“Nanobiomagnetism” is the intersection of nanomagnetism and medicine that focuses on biological systems and/or processes. Magnetism is an inherent facet of life, from iron in blood to the ability of magnetotactic bacteria, birds, …

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Understanding And Control Of Lateral Contraction In Stamping Lithography, Zheng Li, Li Tan, Gang-Yu Liu Jan 2006

Understanding And Control Of Lateral Contraction In Stamping Lithography, Zheng Li, Li Tan, Gang-Yu Liu

Materials Research Science and Engineering Center: Faculty Publications

Thin film contraction under external mechanical stress can be used to miniaturize size and increase density of patterned features on top. Nonlinear Finite Element Analysis is used to provide guidance on this contraction process. It was found that the substrate contraction causes stress accumulation along interfaces between protruded features and substrate. These stress accumulation complexes the control of profile changes on patterned features and suggest a design of patterned features arranged beyond a critical distance to avoid cross-interference.

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Magnetic Aging, Ralph Skomski, Jian Zhou, Roger D. Kirby, David J. Sellmyer Jan 2006

Magnetic Aging, Ralph Skomski, Jian Zhou, Roger D. Kirby, David J. Sellmyer

Materials Research Science and Engineering Center: Faculty Publications

Thermally activated magnetization reversal is of great importance in areas such as permanent magnetism and magnetic recording. In spite of many decades of scientific research, the phenomenon of slow magnetization dynamics has remained partially controversial. It is now well-established that the main mechanism is thermally activated magnetization reversal, as contrasted to eddy currents and structural aging, but the identification of the involved energy barriers remains a challenge for many systems. Thermally activated slow magnetization processes proceed over energy barriers whose structure is determined by the micromagnetic free energy. This restricts the range of physically meaningful energy barriers. An analysis of …

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Effects Of Ion-Beam Irradiation On The L10 Phase Transformation And Their Magnetic Properties Of Fept And Ptmn Films (Invited), Chih-Huang Lai, Sheng-Huang Huang, Cheng-Han Yang, C.C. Chiang, Sy_Hwang Liou, David J. Sellmyer, M. L. Yan, L. Yuan, T. Yokata Jan 2006

Effects Of Ion-Beam Irradiation On The L10 Phase Transformation And Their Magnetic Properties Of Fept And Ptmn Films (Invited), Chih-Huang Lai, Sheng-Huang Huang, Cheng-Han Yang, C.C. Chiang, Sy_Hwang Liou, David J. Sellmyer, M. L. Yan, L. Yuan, T. Yokata

Materials Research Science and Engineering Center: Faculty Publications

In this paper, we illustrate how to modify the structure and magnetic properties of L10 FePt and PtMn films using ion-beam irradiation. Highly ordered L10 FePt and PtMn phases were achieved directly by using 2 MeV He-ion irradiation without conventional post-annealing. A high ion-beam current density (~μA/cm2 ) was used to achieve direct beam heating on samples. This irradiation-induced heating process provides efficient microscopic energy transfer and creates excess point defects, which significantly enhances the diffusion and promotes the formation of the ordered L10 phase. In-plane coercivity of FePt films greater than 5700 Oe could be …

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Surface Segregation In Multicomponent Clusters, Peter A. Dowben, Ning Wu, Natalie Palina, H. Modrow, R. Müller, J. Hormes, Yaroslav B. Losovyj Jan 2006

Surface Segregation In Multicomponent Clusters, Peter A. Dowben, Ning Wu, Natalie Palina, H. Modrow, R. Müller, J. Hormes, Yaroslav B. Losovyj

Materials Research Science and Engineering Center: Faculty Publications

Nanostructured materials are not immune from surface segregation, as can be shown for solid samples made from nanosized BaFe12-2xCoxTixO19 barium ferrite particles and a variety of free clusters. Both theory and experiment provide ample demonstration that very limited dimensions of very small clusters does not necessarily impart stability against surface and grain boundary segregation. In fact, with the larger surface to volume ratio in small clusters and lower average atomic coordination, we anticipate that compositional instabilities in small clusters will readily occur.

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Ferroelectric Switch For Spin Injection, Mikhail Ye. Zhuravlev, Sitaram Jaswal, Evgeny Y. Tsymbal, Renat F. Sabirianov Nov 2005

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.

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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 Nov 2005

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 …

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Effect Of Interface States On Spin-Dependent Tunneling In Fe/Mgo/Fe Tunnel Junctions, Kirill D. Belashchenko, Julian P. Velev, Evgeny Y. Tsymbal Oct 2005

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 …

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Domain-Wall Magnetoresistance Of Co Nanowires, Renat F. Sabiryanov, Ashok K. Solanki, John D. Burton, Sitaram Jaswal, Evgeny Y. Tsymbal Aug 2005

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 …

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Giant Electroresistance In Ferroelectric Tunnel Junctions, Mikhail Ye Zhuravlev, Renat F. Sabirianov, Sitaram Jaswal, Evgeny Y. Tsymbal Jun 2005

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.

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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 Jun 2005

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 …

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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 Jun 2005

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. …

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Role Of Interface Bonding In Spin-Dependent Tunneling (Invited), Evgeny Y. Tsymbal, Kirill D. Belashchenko May 2005

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 …

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A Symmetric Green Function For The Non-Collinear Magnetic Multilayer, Mikhail Ye Zhuravlev, John D. Burton, A. V. Vedyayev, Evgeny Y. Tsymbal May 2005

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 …

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Ballistic Anisotropic Magnetoresistance, Julian P. Velev, Renat F. Sabirianov, Sitaram Jaswal, Evgeny Y. Tsymbal Apr 2005

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.

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Texture Formation In Fept Thin Films Via Thermal Stress Management, P. Rasmussen, X. Rui, Jeffrey E. Shield Feb 2005

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 …

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High-Anisotropy Nanocluster Films For High-Density Perpendicular Recording, David J. Sellmyer, Minglang Yan, Yinfan Xu, Ralph Skomski Feb 2005

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.

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Impurity-Assisted Interlayer Exchange Coupling Across A Tunnel Barrier, Mikhail Ye Zhuravlev, Evgeny Y. Tsymbal, A. V. Vedyayev Jan 2005

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.

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Boron-Rich Semiconducting Boron Carbide Neutron Detector, Andrew D. Harken, Ellen E. Day, Brian W. Robertson, Shireen Adenwalla Jan 2005

Boron-Rich Semiconducting Boron Carbide Neutron Detector, Andrew D. Harken, Ellen E. Day, Brian W. Robertson, Shireen Adenwalla

Shireen Adenwalla Papers

Data on the neutron detection capabilities of a variety of boron carbide/Si heterojunction diodes is presented. The pulse height spectra are compared with previously measured conversion layer devices and the variations in shape and position of the peaks are discussed.

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The Effects Of Humidity On The Dielectric Response In Ferroelectric Polymer Films Made By Langmuir-Blodgett Deposition, Kristin L. Kraemer, Alexander V. Sorokin, Christina M. Othon, Stephen Ducharme, Vladimir M. Fridkin Jan 2005

The Effects Of Humidity On The Dielectric Response In Ferroelectric Polymer Films Made By Langmuir-Blodgett Deposition, Kristin L. Kraemer, Alexander V. Sorokin, Christina M. Othon, Stephen Ducharme, Vladimir M. Fridkin

Stephen Ducharme Publications

No abstract provided.

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Nanomagnetic Structures: Fabrication And Interactions, David J. Sellmyer, Y. C. Sui, Yinfan Xu, M. L. Yan, Kory D. Sorge, Ralph Skomski Jan 2005

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.

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Mercury And C2B10 Icosahedra Interaction, Carolina C. Ilie, Petru Lunca-Popa, Jiandi Zhang, Bernard Doudin, Peter A. Dowben Jan 2005

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.

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Investigation Of Ferroelectricity In Newly Synthesized Nitrile Polymer Systems, Matt Poulsen, Stephen Ducharme, Alexander V. Sorokin, Sahadeva Reddy, James M. Takacs, Y. Wen, Jihee Kim, Shireen Adenwalla Jan 2005

Investigation Of Ferroelectricity In Newly Synthesized Nitrile Polymer Systems, Matt Poulsen, Stephen Ducharme, Alexander V. Sorokin, Sahadeva Reddy, James M. Takacs, Y. Wen, Jihee Kim, Shireen Adenwalla

Stephen Ducharme Publications

The ferroelectric and piezoelectric properties of newly synthesized polymer systems have been studied. To date PVDF and its copolymers P(VDF-TrFE) have provided the bulk of the knowledge pertaining to ferroelectricity in polymers. Recently, ultrathin ferroelectric films of P(VDF-TrFE) 70:30 have been fabricated using the Langmuir-Blodgett technique [4]. In this study, various new polymers have been synthesized by chemically altering the PVDF structure. This alteration was performed in order to enhance the amphiphilic nature of the polymer and thus improve the LB film quality and control. Various chemical groups have been used to replace the electropositive hydrogen and electronegative fluorine found …

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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 Jan 2005

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. …

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Research Experiences For Teachers In Materials Science: A Case Study, Michelle A. Strand, Steve Wignall, Diandra Leslie-Pelecky Jan 2005

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.

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Multiscale Phenomena In Bruggeman Composites, Ralph Skomski, Jiangyu Li, Jian Zhou, David J. Sellmyer Jan 2005

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 …

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Oscillatory Interlayer Exchange Coupling In [Pt/Co]N/Nio/[Co/Pt]N Multilayers With Perpendicular Anisotropy: Dependence On Nio And Pt Layer Thicknesses, Z. Y. Liu, Lanping Yue, D. J. Keavney, Shireen Adenwalla Dec 2004

Oscillatory Interlayer Exchange Coupling In [Pt/Co]N/Nio/[Co/Pt]N Multilayers With Perpendicular Anisotropy: Dependence On Nio And Pt Layer Thicknesses, Z. Y. Liu, Lanping Yue, D. J. Keavney, Shireen Adenwalla

Materials Research Science and Engineering Center: Faculty Publications

Interlayer exchange coupling has been studied in a series of [Pt( tPt Å)/Co(4 Å)]n/NiO( tNiO)/[Co(4 Å)/Pt( tPt Å)]n multilayers with perpendicular anisotropy. The coupling oscillates between antiferromagnetic and ferromagnetic as a function of tNiO with a period of ~5 Å, and the oscillatory behavior is related to the antiferromagnetic ordering of the NiO layer. This interlayer coupling between two Co/Pt multilayers is shown to occur domain by domain by magnetic force microscopy imaging. For the strongest antiferromagnetic coupling at tNiO = 11 Å, an oscillation with a period of ~6 Å is superposed …

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Quantum Entanglement Of Anisotropic Magnetic Nanodots, Ralph Skomski, Andrei Y. Istomin, Anthony F. Starace, David J. Sellmyer Dec 2004

Quantum Entanglement Of Anisotropic Magnetic Nanodots, Ralph Skomski, Andrei Y. Istomin, Anthony F. Starace, David J. Sellmyer

Materials Research Science and Engineering Center: Faculty Publications

Anisotropic magnetic nanodots are promising physical realizations of qubits for quantum computing at finite temperature owing to their well-separated low-lying energy levels and scalability. The entanglement of two interacting magnetic nanodots is investigated and shown both analytically and numerically to be resonantly dependent on their interaction strength and on differences in their properties. These results provide criteria for fabricating and coupling magnetic nanodots so that their low-lying eigenstates can be significantly entangled.

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Disorder-Induced Depression Of The Curie Temperature In Mechanically Milled Gdal2, Marco Morales Torres, D. S. Williams, Paul M. Shand, C. Stark, Thomas M. Pekarek, Lanping Yue, Valeri G. Petkov, Diandra Leslie-Pelecky Nov 2004

Disorder-Induced Depression Of The Curie Temperature In Mechanically Milled Gdal2, Marco Morales Torres, D. S. Williams, Paul M. Shand, C. Stark, Thomas M. Pekarek, Lanping Yue, Valeri G. Petkov, Diandra Leslie-Pelecky

Materials Research Science and Engineering Center: Faculty Publications

The effect of disorder on the ferromagnetic transition is investigated in mechanically milled GdAl2. GdAl2is a ferromagnet when crystalline and a spin glass when amorphous. Mechanical milling progressively disorders the alloy, allowing observation of the change from ferromagnetic to a disordered magnetic state. X-ray diffraction and pair-distribution-function analysis are used to determine the grain size, lattice parameter, and mean-squared atomic displacements. The magnetization as a function of temperature is described by a Gaussian distribution of Curie temperatures. The mean Curie temperature decreases with decreasing lattice parameter, where lattice parameter serves as a measure of defect concentration. …

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