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Articles 271 - 300 of 307

Full-Text Articles in Materials Science and Engineering

First-Principles Study Of Adsorption Of Methanethiol On Co(0001), Ligen Wang, Evgeny Y. Tsymbal, Sitaram Jaswal Aug 2004

First-Principles Study Of Adsorption Of Methanethiol On Co(0001), Ligen Wang, Evgeny Y. Tsymbal, Sitaram Jaswal

Materials Research Science and Engineering Center: Faculty Publications

Investigation of the resident site and the adsorption phase structure of thiolates is of fundamental importance for understanding the formation of self-assembled organic monolayers on metal substrate surfaces. In the present study, we have investigated adsorption of methanethiol, CH3SH, on the ferromagnetic Co (0001) surface using density functional theory calculations.We find that the dissociative adsorption of CH3SH forming an adsorbed methylthiolate (CH3S) and an adsorbed H atom is energetically favorable, and that the CH3S molecule adsorbed at the threefold fcc and hcp hollow sites is most stable. The adsorption energy at the …

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Field-Controlled Domain-Wall Resistance In Magnetic Nanojunctions, John D. Burton, Arti Kashyap, Mikhail Ye. Zhuravlev, Ralph Skomski, Evgeny Y. Tsymbal, Sitaram Jaswal, O.N. Mryasov, R.W. Chantrell Jul 2004

Field-Controlled Domain-Wall Resistance In Magnetic Nanojunctions, John D. Burton, Arti Kashyap, Mikhail Ye. Zhuravlev, Ralph Skomski, Evgeny Y. Tsymbal, Sitaram Jaswal, O.N. Mryasov, R.W. Chantrell

Materials Research Science and Engineering Center: Faculty Publications

The electrical resistance of a constrained domain wall in a nanojunction is investigated using micromagnetic modeling and ballistic conductance calculations. The nanojunction represents two ferromagnetic electrodes connected by a ferromagnetic wire of 10 nm in length and of a few nanometers in cross section. We find that the anisotropy of the electrodes favors a localization of the domain wall within the constriction (wire) revealing a positive domain-wall resistance. An applied magnetic field moves the domain wall toward one of the electrodes and reduces its width. This compression of the domain wall leads to a sizeable enhancement of the domain-wall resistance.

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The Effect Of Transition Metal Additions On The Microstructure And Properties Of Nanocomposite Pr–Fe–B Permanent Magnets, Jeffrey E. Shield, Yi Liu, R. Marr, Z. Chen, Baomin Ma Jul 2004

The Effect Of Transition Metal Additions On The Microstructure And Properties Of Nanocomposite Pr–Fe–B Permanent Magnets, Jeffrey E. Shield, Yi Liu, R. Marr, Z. Chen, Baomin Ma

Materials Research Science and Engineering Center: Faculty Publications

Permanent magnets with the general composition Pr9 (Fe0.95Co0.05)85.5M0.5B5, where M denotes a transition metal, have been produced by melt spinning. The effect on the microstructure and magnetic properties of eight different alloying elements has been examined. The grain size and distribution have been correlated to the maximum energy product obtained. The grain size of the Pr9 (Fe0.95Co0.05) 85.5B5 control alloy was determined to be 17.5 nm, and it was found that the grain size was not significantly reduced compared to the control …

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Domain-Wall Pinning At Inhomogenities Of Arbitrary Cross-Sectional Geometry, Ralph Skomski, Jian Zhou, Arti Kashyap, David J. Sellmyer Jul 2004

Domain-Wall Pinning At Inhomogenities Of Arbitrary Cross-Sectional Geometry, Ralph Skomski, Jian Zhou, Arti Kashyap, David J. Sellmyer

Materials Research Science and Engineering Center: Faculty Publications

Abstract—The coercivity of cellular Sm-Co based permanent magnets is investigated by model calculations. The grain boundaries responsible for the pinning coercivity are modeled as planar inhomogenities with arbitrary cross-sectional geometry. The calculation yields a physically transparent integral equation for the pinning energy, whose derivative is the pinning force. The theory rationalizes experimental data on a semiquantitative level, but without adjustable parameters, and bridges the gap between smooth concentration gradients and abrupt interfaces. Explicit results are obtained for sinoidal profiles, for very thin grain boundaries, and for profiles intermediate between attractive and repulsive pinning. The corrections predicted by the present model …

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Magnetization Reversal And Giant Coercivity In Sm-Co/Cu-Ti Particulate Films, Jian Zhou, Arti Kashyap, Yi Liu, Ralph Skomski, David J. Sellmyer Jul 2004

Magnetization Reversal And Giant Coercivity In Sm-Co/Cu-Ti Particulate Films, Jian Zhou, Arti Kashyap, Yi Liu, Ralph Skomski, David J. Sellmyer

Materials Research Science and Engineering Center: Faculty Publications

Highly coercive granular SmCo/CuTi films were produced by thermal processing of sputtered SmCo5 (CuTi) multilayers and investigated experimentally and theoretically. Electron microscopy shows that the processed films consist of spherical grains that have diameters of 5–10 nm and are embedded in a matrix. Both the grains and the matrix phase exhibit the CaCu5 structure, but the matrix is probably Cu-rich. The films have high coercivities of up to 50.4 kOe at 300 K. Analytical calculations and micromagnetic simulations yield a transition from a nucleation-type weak-interaction regime to a discrete-pinning-type strong-interaction regime. The transition occurs at packing fractions similar …

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L10 Ordered Fept:C Composite Films With (001) Texture, M. L. Yan, Renat F. Sabiryanov, Yinfan Xu, Xingzhong Li, David J. Sellmyer Jul 2004

L10 Ordered Fept:C Composite Films With (001) Texture, M. L. Yan, Renat F. Sabiryanov, Yinfan Xu, Xingzhong Li, David J. Sellmyer

Materials Research Science and Engineering Center: Faculty Publications

Highly textured (001) FePt:C nanocomposite thin films, deposited directly on thermally oxidized Si wafers, are obtained by multilayer deposition plus subsequent thermal annealing. Nanostructures, crystalline orientations, interactions, and magnetic properties are investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), magnetic force microscopy, and magnetic measurements. The formation of the ordered L10 phase is confirmed by XRD, and only visible (00 ) peaks indicate a high degree of the (001) texture. TEM observation reveals that FePt grains are embedded in the C matrix and appear to be well isolated.

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Nanostructure And Magnetic Properties Of Fept :C Cluster Films, Yinfan Xu, M. L. Yan, David J. Sellmyer Jul 2004

Nanostructure And Magnetic Properties Of Fept :C Cluster Films, Yinfan Xu, M. L. Yan, David J. Sellmyer

Materials Research Science and Engineering Center: Faculty Publications

Magnetic properties and nanostructure of FePt : C cluster-deposited films with C volume fraction of 7%, 14%, 33%, and 45% have been studied. As-deposited FePt : C films were prepared by a multilayer method in which FePt layers were deposited from a cluster source employing a gas-aggregation technique and C layers from a normal sputtering gun. In the as-deposited films, FePt clusters with fcc structure are embedded in the C matrix. The high anisotropy FePt L10 cluster structure was realized in the films via post-deposition annealing and the nanostructure of the films was observed by high-resolution transmission electron microscope …

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Magnetization Processes In Melt-Spun Sm-Co-Based Alloys With The Tbcu7-Type Structure, A. Hsiaoa, S. Aich, L. H. Lewis, Jeffrey E. Shield Jul 2004

Magnetization Processes In Melt-Spun Sm-Co-Based Alloys With The Tbcu7-Type Structure, A. Hsiaoa, S. Aich, L. H. Lewis, Jeffrey E. Shield

Materials Research Science and Engineering Center: Faculty Publications

The initial magnetization processes in melt-spun Sm-Co alloys with remanent ratios above 0.7 have been studied. Alloys of (Sm(1/(6+x) Co (5+x)/(6+x) ) 94Nb3C3 (x = 067, 1.7, 2.3 and 3) alloys modified with Nb and C were melt spun at wheel speeds of 20 and 40 m/s, and the compositions span the range between the Sm2Co17 and SmCo5 stoichiometries. Structurally, all alloys formed in the TbCu7-type structure, although a small amount of Sm2Co7 was observed in Sm-rich samples, and a small amount of fcc Co formed …

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Exchange Model For Oscillatory Interlayer Coupling And Induced Unidirectional Anisotropy In [Pt/Co]3/Nio/[Pt/Co]3 Multilayers, Mikhail Ye Zhuravlev, Evgeny Y. Tsymbal, Sitaram Jaswal May 2004

Exchange Model For Oscillatory Interlayer Coupling And Induced Unidirectional Anisotropy In [Pt/Co]3/Nio/[Pt/Co]3 Multilayers, Mikhail Ye Zhuravlev, Evgeny Y. Tsymbal, Sitaram Jaswal

Materials Research Science and Engineering Center: Faculty Publications

In a recent Letter [1] Liu and Adenwalla found an interesting oscillatory behavior of the interlayer exchange coupling (IEC) through an insulating NiO (111) layer with a period of 2 monolayers (ML). They interpreted this phenomenon in terms of multiple reflections of electronic waves from a periodic atomic potential in the spirit of the model of Ref. [2]. However, this interpretation is not consistent with the tunneling mechanism used by the authors which would result in a modulated exponential decrease of the IEC but no periodic change in sign. In this Comment we show that the observed oscillatory IEC can …

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Effect Of Interface Bonding On Spin-Dependent Tunneling From The Oxidized Co Surface, Kirill D. Belashchenko, Evgeny Y. Tsymbal, Mark Van Schilfgaarde, Derek A. Stewart, Ivan I. Oleynik, Sitaram Jaswal May 2004

Effect Of Interface Bonding On Spin-Dependent Tunneling From The Oxidized Co Surface, Kirill D. Belashchenko, Evgeny Y. Tsymbal, Mark Van Schilfgaarde, Derek A. Stewart, Ivan I. Oleynik, Sitaram Jaswal

Materials Research Science and Engineering Center: Faculty Publications

We demonstrate that the factorization of the tunneling transmission into the product of two surface transmission functions and a vacuum decay factor allows one to generalize Jullière's formula and explain the meaning of the "tunneling density of states" in some limiting cases. Using this factorization we calculate spin-dependent tunneling from clean and oxidized fcc Co surfaces through vacuum into Al using the principal-layer Green's-function approach. We demonstrate that a monolayer of oxygen on the Co(111) surface creates a spin-filter effect due to the Co-O bonding which produces an additional tunneling barrier in the minority-spin channel. This changes the minority-spin dominated …

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Anisotropy Of Exchange Stiffness And Its Effect On The Properties Of Magnets, K. D. Belashchenko Apr 2004

Anisotropy Of Exchange Stiffness And Its Effect On The Properties Of Magnets, K. D. Belashchenko

Kirill Belashchenko Publications

Using the spin-spiral formulation of the tight-binding linear muffin-tin orbital method, the principal components of the exchange stiffness tensor are calculated for typical hard magnets including tetragonal CoPt-type and hexagonal YCo5 alloys. The exchange stiffness is strongly anisotropic in all studied alloys. This anisotropy makes the domain wall surface tension anisotropic. Competition between this anisotropic surface tension and magnetostatic energy controls the formation and dynamics of nanoscale domain structures in hard magnets. Anisotropic domain wall bending is described in detail from the general point of view and with application to cellular Sm–Co magnets. It is shown that the repulsive …

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Mapping Surface Polarization In Thin Films Of The Ferroelectric Polymer P(Vdf-Trfe)., Bradley W. Peterson, Stephen Ducharme, Vladimir M. Fridkin, Timothy J. Reece Jan 2004

Mapping Surface Polarization In Thin Films Of The Ferroelectric Polymer P(Vdf-Trfe)., Bradley W. Peterson, Stephen Ducharme, Vladimir M. Fridkin, Timothy J. Reece

Stephen Ducharme Publications

Pyroelectric Scanning Microscopy (PSM) has been developed to enable mapping of surface polarization in ferroelectric thin films, in particular the copolymer polyvinylidene fluoride trifluororethylene, or P(VDF-TrFE). The Chynoweth method for dynamically measuring pyroelectric current is employed in conjunction with a micropositioning system to construct two-dimensional images of the film polarization. These images have revealed enhancement of the polarization near the edges of the film below the average coercive field, with the center's polarization increasing thereafter to meet the edge value at saturation.

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Electron Irradiation Effects On Ferroelectric Copolymer Langmuir-Blodgett Films, Christina M. Othon, Stephen Ducharme Jan 2004

Electron Irradiation Effects On Ferroelectric Copolymer Langmuir-Blodgett Films, Christina M. Othon, Stephen Ducharme

Stephen Ducharme Publications

The effect of irradiation on the ferroelectric properties of Langmuir-Blodgett films of the copolymer poly(vinylidene fluoride-trifluorethelene) is investigating using 1.26 MeV electrons with dosages from 16 to 110 Mrad. Irradiation causes a systematic decrease in the phase transition temperature, coercive field and polarization of these thin films.

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Ferroelectricity At Molecular Level, L. M. Blinov, A. V. Bune, Peter A. Dowben, Stephen Ducharme, Vladimir M. Fridkin, S. P. Palto, K. A. Verkhovskaya, G. V. Vizdrik, S. G. Yudin Jan 2004

Ferroelectricity At Molecular Level, L. M. Blinov, A. V. Bune, Peter A. Dowben, Stephen Ducharme, Vladimir M. Fridkin, S. P. Palto, K. A. Verkhovskaya, G. V. Vizdrik, S. G. Yudin

Stephen Ducharme Publications

he synthesis of ultrathin ferroelectric nanostructures by the Langmuir-Blodgett method and their properties are reviewed. It is shown that ferroelectricity exists in one monolayer of the ferroelectric P(VDF-TrFE) copolymer, i.e., at the molecular level. The specific characteristics of switching of ultrathin ferroelectric films are established.

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Magnetic Transitions In Disordered Gdal2, D. S. Williams, Paul M. Shand, Thomas M. Pekarek, Ralph Skomski, Valeri G. Petkov, Diandra Leslie-Pelecky Dec 2003

Magnetic Transitions In Disordered Gdal2, D. S. Williams, Paul M. Shand, Thomas M. Pekarek, Ralph Skomski, Valeri G. Petkov, Diandra Leslie-Pelecky

Materials Research Science and Engineering Center: Faculty Publications

The role of disorder in magnetic ordering transitions is investigated using mechanically milled GdAl2. Crystalline GdAl2 is a ferromagnet while amorphous GdAl2 is a spin glass. Nanostructured GdAl2 shows a paramagnetic-to-ferromagnetic transition and glassy behavior, with the temperature and magnitude of each transition dependent on the degree and type of disorder. Disorder is parametrized by a Gaussian distribution of Curie temperatures TC with mean TC and breadth Δ TC. A nonzero coercivity is observed at temperatures more than 20 K above the highest TC of any known Gd-Al phase; however, …

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Spin Blockade In Ferromagnetic Nanocontacts, M. Ye Zhuralev, Evgeny Y. Tsymbal, Sitaram Jaswal, A.V. Vedyayev, B. Dieny Oct 2003

Spin Blockade In Ferromagnetic Nanocontacts, M. Ye Zhuralev, Evgeny Y. Tsymbal, Sitaram Jaswal, A.V. Vedyayev, B. Dieny

Materials Research Science and Engineering Center: Faculty Publications

Using a free-electron model and a linear response theory we investigate spin-dependent electronic transport in magnetic nanocontacts in the ballistic regime of conduction. We emphasize the fact that in atomic-size ferromagnetic contacts it is possible to achieve the conductance value of e2/h, which implies a fully spin-polarized electric current. We explore some consequences of this phenomenon. In particular, we show that the presence of a nonmagnetic region in the nanocontact separating two ferromagnetic electrodes can lead to a spin blockade resulting in very large values of magnetoresistance.

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Surface Structure Of Ultrathin Copolymer Films Of Ferroelectric Vinylidene Fluoride (70%) With Trifluoroethylene (30%) On Graphite, Lei Cai, Hongwei Qu, Chenxi Lu, Stephen Ducharme, Peter A. Dowben, Jiandi Zhang Oct 2003

Surface Structure Of Ultrathin Copolymer Films Of Ferroelectric Vinylidene Fluoride (70%) With Trifluoroethylene (30%) On Graphite, Lei Cai, Hongwei Qu, Chenxi Lu, Stephen Ducharme, Peter A. Dowben, Jiandi Zhang

Materials Research Science and Engineering Center: Faculty Publications

The structure and local structural distortions, through the polarization manipulation, of crystalline films of ferroelectric vinylidene fluoride (70%) with trifluoroethylene (30%) [P(VDF-TrFE)] copolymer on graphite were studied by scanning tunneling microscopy (STM). A quasispiral twist in C[Single Bond]C bonds with rotations about the polymer chain axis was observed by high-resolution STM, indicating a surface relaxation of the strained copolymer films. Such a relaxation behavior appears to be linked to the observed local dipole rotations accompanied by the reversal of the local polarization with biasing the STM tip. A structure model is proposed based upon the observations.

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Finite-Temperature Anisotropy Of Ptco Magnets, Ralph Skomski, Arti Kashyap, David J. Sellmyer Sep 2003

Finite-Temperature Anisotropy Of Ptco Magnets, Ralph Skomski, Arti Kashyap, David J. Sellmyer

Materials Research Science and Engineering Center: Faculty Publications

The temperature dependence of the magnetocrystalline anisotropy of PtCo and its atomic origin are investigated by first-principle and model calculations. The Pt spin moment necessary to realize the leading 5d anisotropy contribution is due to neighboring Co atoms. At finite temperatures, Co spin disorder strongly reduces the Pt moment and the anisotropy. This is in contrast to the situation encountered in 3d and 3d–4f magnets, where the atomic magnetic moments remain largely conserved, even above the Curie temperature. A consequence of the L10 mechanism is that theK1 (T) curve of exhibits a negative curvature, in contrast to the …

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Exchange Interactions And Curie Temperature Of Y–Co Compounds, Arti Kashyap, Ralph Skomski, Renat F. Sabiryanov, Sitaram Jaswal, David J. Sellmyer Sep 2003

Exchange Interactions And Curie Temperature Of Y–Co Compounds, Arti Kashyap, Ralph Skomski, Renat F. Sabiryanov, Sitaram Jaswal, David J. Sellmyer

Materials Research Science and Engineering Center: Faculty Publications

The Curie temperature of rare-earth Co intermetallics is investigated by self-consistent spin-polarized electronic-structure calculations on Y–Co compounds. The total exchange interaction of a given site with all other sites (Jo) is calculated by the linear-muffin-tin-orbital method using the local force theorem and employed to obtain mean-field Curie-temperature estimates. The theoretical predictions for YCo3, YCo5, and Y2Co17 are in fair agreement with the experimental Curie temperatures. For YCo5, the variation of exchange interactions (Jij) with distance is analyzed, and it is discussed how the presence of nonequivalent cobalt …

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Oscillatory Interlayer Exchange Coupling And Its Temperature Dependence In [Pt/Co]3/Nio/[Co/Pt]3 Multilayers With Perpendicular Anisotropy, Z. Y. Liu, Shireen Adenwalla Jul 2003

Oscillatory Interlayer Exchange Coupling And Its Temperature Dependence In [Pt/Co]3/Nio/[Co/Pt]3 Multilayers With Perpendicular Anisotropy, Z. Y. Liu, Shireen Adenwalla

Materials Research Science and Engineering Center: Faculty Publications

Interlayer exchange coupling that oscillates between antiferromagnetic and ferromagnetic as a function of NiO thickness has been observed in [Pt(5 Å)/Co(4 Å)]3/NiO(tNiO Å)/[Co(4 Å)/Pt(5 Å)]3 multilayers with out-of-plane anisotropy. The period of oscillation corresponds to ~2 monolayers of NiO. This oscillatory behavior is possibly attributed to the antiferromagnetic ordering in NiO. The antiferromagnetic interlayer exchange coupling for the 11 Å NiO layer shows an increase in coupling strength with increasing temperature, in agreement with the quantum interference model of Bruno for insulating spacer layers. A coexistence of exchange biasing and antiferromagnetic interlayer exchange coupling has …

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Closely Linear Temperature Dependence Of Exchange Bias And Coercivity In Out-Of-Plane Exchange-Biased [Pt/Co] 3/Nio (11 Å) Multilayer, Z.Y. Liu, Shireen Adenwalla Jul 2003

Closely Linear Temperature Dependence Of Exchange Bias And Coercivity In Out-Of-Plane Exchange-Biased [Pt/Co] 3/Nio (11 Å) Multilayer, Z.Y. Liu, Shireen Adenwalla

Materials Research Science and Engineering Center: Faculty Publications

Strong out-of-plane exchange biasing has been observed in out-of-plane exchange biased [Pt (5 Å)/Co (4 Å)] 3/NiO (11 Å) multilayer with perpendicular easy axis. Both the exchange field HE and coercivity HC display a closely linear temperature dependence except at very low temperatures. A thin NiO layer coated on the top of a Pt/Co multilayer has a great effect on the domain pattern of the Pt/Co multilayer, which is in a more irregular configuration with much smaller domain sizes than the uncoupled Pt/Co multilayer. A simulation according to Malozemoff's random field model gives a good agreement to …

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Comment On: 'Depolarization Corrections To The Coercive Field In Thin-Film Ferroelectrics', Stephen Ducharme, Vladimir Fridkin Jul 2003

Comment On: 'Depolarization Corrections To The Coercive Field In Thin-Film Ferroelectrics', Stephen Ducharme, Vladimir Fridkin

Stephen Ducharme Publications

The Letter by Dawber et al. [J. Phys.: Condens. Matter 15 L393 (2003)] notes that incomplete screening in the electrodes of a ferroelectric capacitor can result in an underestimate for the true coercive field in films of nanometer thickness. We show that their estimate of the magnitude of this correction it too large in the case of ferroelectric copolymer Langmuir- Blodgett films and, as a result, invalidates the claim that finite-size scaling of the ferroelectric coercive field is evident in films thinner than 15 nm.

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Ferromagnetic Domain-Wall Behavior During Reversal And Thermally Activated Antiferromagnetic Reversal In An Exchange-Biased Nio/Nife Bilayer, Z. Y. Liu, Shireen Adenwalla May 2003

Ferromagnetic Domain-Wall Behavior During Reversal And Thermally Activated Antiferromagnetic Reversal In An Exchange-Biased Nio/Nife Bilayer, Z. Y. Liu, Shireen Adenwalla

Materials Research Science and Engineering Center: Faculty Publications

The magnetization reversal mechanism in an exchange-biased NiO/Ni81Fe19 bilayer has been investigated using the magneto-optic Kerr effect and magnetic force microscopy imaging. The asymmetric reversal along the unidirectional axis and the two-step reversal process along the hard axis are promoted by ferromagnetic domain-wall behavior in the decreasing and increasing field branches of the as-deposited hysteresis loop, which is strongly related to the exchange coupling at the interface and the distribution of orientation of the net magnetization at the interface carried by the antiferromagnetic domains. The temperature dependence of the exchange bias and coercivity shows the thermally activated …

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Atomic, Electronic, And Magnetic Properties Of Magnetic Tunnel Junctions, I.I. Oleynik, Evgeny Y. Tsymbal May 2003

Atomic, Electronic, And Magnetic Properties Of Magnetic Tunnel Junctions, I.I. Oleynik, Evgeny Y. Tsymbal

Materials Research Science and Engineering Center: Faculty Publications

We report results of first-principles density-functional studies of the atomic and electronic structure of Co/Al2O3/Co and Co/SrTiO3/Co magnetic tunnel junctions (MTJs). The atomic structure has been studied for different interface terminations and the interfacial energetics was quantified based on the work of separation. Based on energetics of cohesion, the O-terminated and TiO2-terminated interfaces were identified as the most stable structures for Co/Al2O3/Co and Co/SrTiO3/Co MTJs, respectively. The electronic structure was analyzed using local densities of states. We found that the electronic structure of the O-terminated Co/Al …

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Resonant Inversion Of Tunneling Magnetoresistance, Evgeny Y. Tsymbal, Andrei Sokolov, Ildar F. Sabiryanov, Bernard Doudin May 2003

Resonant Inversion Of Tunneling Magnetoresistance, Evgeny Y. Tsymbal, Andrei Sokolov, Ildar F. Sabiryanov, Bernard Doudin

Materials Research Science and Engineering Center: Faculty Publications

Resonant tunneling via localized states in the barrier can invert magnetoresistance in magnetic tunnel junctions. Experiments performed on electrodeposited Ni/NiO/Co nanojunctions of area smaller than 0.01 μm2 show that both positive and negative values of magnetoresistance are possible. Calculations based on Landauer-Bu¨ttiker theory explain this behavior in terms of disorder-driven statistical variations in magnetoresistance with a finite probability of inversion due to resonant tunneling.

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Variation Of Domain Formation In A 15 Nm Nife Layer Exchange Coupled With Nio Layers Of Different Thicknesses, Z.Y. Liu, Shireen Adenwalla Mar 2003

Variation Of Domain Formation In A 15 Nm Nife Layer Exchange Coupled With Nio Layers Of Different Thicknesses, Z.Y. Liu, Shireen Adenwalla

Materials Research Science and Engineering Center: Faculty Publications

The correlation between ferromagnetic domain formation and exchange bias in a series of NiFe/NiO samples with varying NiO thicknesses has been investigated using the magneto-optic Kerr effect and magnetic force microscopy. Below a critical thickness (15 nm) of NiO, the exchange bias HE is zero and ripple domains exist in the NiFe layer. Above this critical thickness, cross-tie type domain walls appear concurrently with the appearance of exchange bias. Both the number of cross-tie domain walls and the exchange bias increase with an increase in NiO thickness, reaching a maximum at 35 nm NiO, after which both show a …

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Angular Dependence Of Magnetization Reversal Process In Exchange Coupled Ferromagnetic/Antiferromagnetic Bilayers, Z.Y. Liu, Shireen Adenwalla Mar 2003

Angular Dependence Of Magnetization Reversal Process In Exchange Coupled Ferromagnetic/Antiferromagnetic Bilayers, Z.Y. Liu, Shireen Adenwalla

Materials Research Science and Engineering Center: Faculty Publications

The angular dependence of the magnetization reversal process in the exchange biased ferromagnetic/antiferromagnetic bilayers has been investigated carefully using the Stoner–Wohlfarth rotation model. Depending strongly on the orientation of the applied field and the competition between the unidirectional and uniaxial anisotropic energies, the magnetization rotation can occur at either the same side or the different sides of the field direction for the decreasing and increasing field branches of the hysteresis loop. The calculated results and the magneto-optical Kerr effect have been used to understand the magnetization reversal process in the NiFe/NiO bilayers, which is caused mainly by the magnetization rotation.

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Out-Of-Plane Exchange Coupling Between Epitaxial Ni(50 Å) And Nio(600 Å) Bilayers, Z.Y. Liu, Shireen Adenwalla Feb 2003

Out-Of-Plane Exchange Coupling Between Epitaxial Ni(50 Å) And Nio(600 Å) Bilayers, Z.Y. Liu, Shireen Adenwalla

Materials Research Science and Engineering Center: Faculty Publications

We have investigated the exchange coupling between an epitaxial Ni (50 Å) film with an out-of-plane magnetic easy axis and a NiO (600 Å) film by polar magneto-optic Kerr-effect measurements. The temperature dependences of exchange field HE for both as-deposited and field-cooled states exhibit the same blocking temperature TB~130 °C. The exchange field HE for the field-cooled state is lower than that for the as-deposited state. The hard-axis in-plane loop shows a much smaller value of HE. No coercivity enhancement is observed. The data are suggestive of linear coupling across the ferromagnet/antiferromagnet interface.

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Bistable Memory Effect In Chromium Oxide Junctions, Andrei Sokolov, C.-S. Yang, E. Ovtchenkov, L. Yuan, Sy-Hwang Liou, Bernard Doudin Jan 2003

Bistable Memory Effect In Chromium Oxide Junctions, Andrei Sokolov, C.-S. Yang, E. Ovtchenkov, L. Yuan, Sy-Hwang Liou, Bernard Doudin

Materials Research Science and Engineering Center: Faculty Publications

Magnetotransport properties of granular CrO2 /Cr2O3 films made of CrO2 crystals covered by 1- 2 nm native insulating Cr2O3 are presented. Electrical properties of a limited number of grains measured in series and parallel (10 to 15 grains) reveal intergrain tunneling characteristics. At lowest temperatures, a well pronounced zero bias anomaly indicates that impurities in the junctions block the electronic flow.

Hysteresis in the IV curves are observed at intermediate temperatures on zero-field cooled samples. Changing the polarity of a short excitation pulse (100ns) of amplitude smaller than 1 V triggers a …

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Substrate Dependent Bonding Of Chemisorbed 1,1’-Biphenyl-4,4’-Dimethanethiol, A. N. Caruso, R. Rajesekaran, Jody G. Redepenning, Yaroslav B. Losovyj, Peter A. Dowben Jan 2003

Substrate Dependent Bonding Of Chemisorbed 1,1’-Biphenyl-4,4’-Dimethanethiol, A. N. Caruso, R. Rajesekaran, Jody G. Redepenning, Yaroslav B. Losovyj, Peter A. Dowben

Materials Research Science and Engineering Center: Faculty Publications

We compare the adsorption of 1,1’-biphenyl-4,4’-dimethanethiol (BPDMT) on gold and cobalt surfaces. The molecular orbitals, identified from combined photoemission and inverse photoemission studies, exhibit shifts in binding energies with different deposition methods and substrates. These shifts indicate that this potential molecular dielectric exhibits stronger bonding to cobalt surfaces than gold surfaces.

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