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Articles 91 - 101 of 101
Full-Text Articles in Physics
Multiferroic Tunnel Junctions With Poly(Vinylidene Fluoride), Julian P. Velev, Juan M. López-Encarnación, John D. Burton, Evgeny Y. Tsymbal
Multiferroic Tunnel Junctions With Poly(Vinylidene Fluoride), Julian P. Velev, Juan M. López-Encarnación, John D. Burton, Evgeny Y. Tsymbal
Evgeny Tsymbal Publications
We perform first-principles calculations based on density functional theory of the spin-resolved conductance of poly(vinylidene fluoride)- (PVDF) based multiferroic tunnel junctions (MFTJs).We consider Co/PVDF/O/Co (0001) MFTJs with one oxidized interface, representing the different experimental growth conditions for the two interfaces. We demonstrate that this natural asymmetry leads to multiple resistance states associated with different magnetization configurations of the electrodes and ferroelectric polarization orientations of the barrier. Our results indicate very high tunability of the tunneling magnetoresistance and electroresistance effects, which could be useful for logic and memory applications.
Interface Dipole Effect On Thin Film Ferroelectric Stability: First-Principles And Phenomenological Modeling, Xiaohui Liu, Yong Wang, Pavel V. Lukashev, John D. Burton, Evgeny Y. Tsymbal
Interface Dipole Effect On Thin Film Ferroelectric Stability: First-Principles And Phenomenological Modeling, Xiaohui Liu, Yong Wang, Pavel V. Lukashev, John D. Burton, Evgeny Y. Tsymbal
Evgeny Tsymbal Publications
Utilization of the switchable spontaneous polarization of ferroelectric materials offers a promising avenue for the future of nanoelectronic memories and logic devices provided that nanoscale metal-ferroelectric-metal heterostructures can be engineered to maintain a bi-stable polarization switchable by an applied electric field. The most challenging aspect of this approach is to overcome the deleterious interface effects which tend to render ferroelectric polarization either unstable or unswitchable and which become ever more important as ferroelectric materials are produced thinner and thinner. Here we use first-principles density functional calculations and phenomenological modeling to demonstrate that a BaO/RuO2 interface termination sequence in SrRuO …
Dispersion Compensation For Attosecond Electron Pulses, Peter Hansen, Cory Baumgarten, Herman Batelaan, Martin Centurion
Dispersion Compensation For Attosecond Electron Pulses, Peter Hansen, Cory Baumgarten, Herman Batelaan, Martin Centurion
Martin Centurion Publications
We propose a device to compensate for the dispersion of attosecond electron pulses. The device uses only static electric and magnetic fields and therefore does not require synchronization to the pulsed electron source. Analogous to the well-known optical dispersion compensator, an electron dispersion compensator separates paths by energy in space. Magnetic fields are used as the dispersing element, while a Wien filter is used for compensation of the electron arrival times. We analyze a device with a size of centimeters, which can be applied to ultrafast electron diffraction and microscopy, and fundamental studies.
Imaging Of Isolated Molecules With Ultrafast Electron Pulses, Christopher J. Hensley, Jie Yang, Martin Centurion
Imaging Of Isolated Molecules With Ultrafast Electron Pulses, Christopher J. Hensley, Jie Yang, Martin Centurion
Martin Centurion Publications
Imaging isolated molecules in three dimensions with atomic resolution is important for elucidating complex molecular structures and intermediate states in molecular dynamics. This goal has so far remained elusive due to the random orientation of molecules in the gas phase. We show that threedimensional structural information can be retrieved from multiple electron diffraction patterns of aligned molecules. The molecules are aligned impulsively with a femtosecond laser pulse and probed with a femtosecond electron pulse two picoseconds later, when the degree of alignment reaches a maximum.
The Sweep Rate Dependence Of The Electrical Control Of Magnetic Coercivity, Abhijit Mardana, Stephen Ducharme, Shireen Adenwalla
The Sweep Rate Dependence Of The Electrical Control Of Magnetic Coercivity, Abhijit Mardana, Stephen Ducharme, Shireen Adenwalla
Stephen Ducharme Publications
The sweep rate dependence of the coercive field in magnetic thin films is well-known. Here we present an experimental investigation of the dependence of electric field control of magnetization on the magnetic field sweep rate. Our sample is a ferroelectric/ferromagnetic heterostructure, with a soft polymer ferroelectric in contact with a transition metal ferromagnet, Co. Previous work on these heterostructures revealed a large change in coercive field and anisotropy when the ferroelectric polarization was switched from up to down. The present work shows that faster sweep rates increase the changes in coercive field that arise from switching the ferroelectric polarization. Our …
Hysteresis And Relaxation In Granular Permanent Magnets, Ralph Skomski, Balamurugan Balamurugan, Thomas A. George, Mircea Chipara, Xiao-Hui Wei, Jeffrey E. Shield, David J. Sellmyer
Hysteresis And Relaxation In Granular Permanent Magnets, Ralph Skomski, Balamurugan Balamurugan, Thomas A. George, Mircea Chipara, Xiao-Hui Wei, Jeffrey E. Shield, David J. Sellmyer
David Sellmyer Publications
Some nontrivial aspects of the magnetic and structural characterization of hard-magnetic nanoparticles are investigated. Dilute ensembles are well-described by mean-field theory, although there is an asymmetry between exchange and magnetostatic interaction fields. Corrections to the mean-field approximation are caused by cooperative effects and have the character of Onsager reaction fields, which are much stronger in micromagnetism than in atomic-scale magnetism. The slow dynamics of zero-field-cooled (ZFC) magnetization curves is strongly affected by the particles0 magnetic anisotropy, which reduces the corresponding energy-barrier height from 25 to 19.1 kBT.
Magnetism Of Dilute Co(Hf) And Co(Pt) Nanoclusters, Balamurugan Balasubramanian, Ralph Skomski, Xingzhong Li, Shah R. V, Priyanka Manchanda, Arti Kashyap, David J. Sellmyer
Magnetism Of Dilute Co(Hf) And Co(Pt) Nanoclusters, Balamurugan Balasubramanian, Ralph Skomski, Xingzhong Li, Shah R. V, Priyanka Manchanda, Arti Kashyap, David J. Sellmyer
David Sellmyer Publications
An investigation of the magnetic properties of Co-rich nanoparticles alloyed with a small fraction of Pt and Hf is presented. Co(Hf) and Co(Pt) nanoparticles with less than 15 at% of dopants were produced using a cluster-deposition method. The nanoparticles have sizes of less than 10 nm and show improved magnetic properties upon doping. Maximum coercivities of 900 Oe (at 300 K) and 2000 Oe (at 10 K) were observed for Co nanoparticles alloyed with 14.1 at% of Hf. Doped nanoparticles also exhibit high anisotropies, such as K1¼9.98 Mergs=cm3 (14.1 at% of Hf) and K1¼8.24 Mergs=cm …
Ultrahard Magnetic Nanostructures, P. K. Sahota, Yi Liu, Ralph Skomski, Priyanka Manchanda, R. Zhang, M. Franchin, H. Fangohr, George C. Hadjipanayis, Arti Kashyap, David J. Sellmyer
Ultrahard Magnetic Nanostructures, P. K. Sahota, Yi Liu, Ralph Skomski, Priyanka Manchanda, R. Zhang, M. Franchin, H. Fangohr, George C. Hadjipanayis, Arti Kashyap, David J. Sellmyer
David Sellmyer Publications
The performance of hard-magnetic nanostructures is investigated by analyzing the size and geometry dependence of thin-film hysteresis loops. Compared to bulk magnets, weight and volume are much less important, but we find that the energy product remains the main figure of merit down to very small features sizes. However, hysteresis loops are much easier to control on small length scales, as epitomized by Fe-Co-Pt thin films with magnetizations of up to 1.78 T and coercivities of up to 2.52 T. Our numerical and analytical calculations show that the feature size and geometry have a big effect on the hysteresis loop. …
Crystal Field Splitting And Optical Bandgap Of Hexagonal Lufeo3 Films, Wenbin Wang, Hongwei Wang, Xiaoying Xu, Leyi Zhu, Lixin He, Elizabeth Wills, Xuemei Cheng, David J. Keavney, Jian Shen, Xifan Wu, Xiaoshan Xu
Crystal Field Splitting And Optical Bandgap Of Hexagonal Lufeo3 Films, Wenbin Wang, Hongwei Wang, Xiaoying Xu, Leyi Zhu, Lixin He, Elizabeth Wills, Xuemei Cheng, David J. Keavney, Jian Shen, Xifan Wu, Xiaoshan Xu
Xiaoshan Xu Papers
Hexagonal LuFeO3 films have been studied using x-ray absorption and optical spectroscopy. The crystal splitting of Fe3+ is extracted as Ee' - Ee" = 0.7 eV and Ea'1 - Ee' = 0.9 eV, and a 2.0 eV optical bandgap is determined assuming a direct gap. First-principles calculations confirm the experiments that the relative energies of crystal field splitting states do follow Ea'1 > Ee' > Ee" with slightly underestimated values and a bandgap of 1.35 eV.
Ultrafast Resonance-Enhanced Multiphoton Ionization In The Azabenzenes: Pyridine, Pyridazine, Pyrimidine, And Pyrazine, Timothy D. Scarborough, David B. Foote,, Cornelis J. Uiterwaal
Ultrafast Resonance-Enhanced Multiphoton Ionization In The Azabenzenes: Pyridine, Pyridazine, Pyrimidine, And Pyrazine, Timothy D. Scarborough, David B. Foote,, Cornelis J. Uiterwaal
C.J.G.J. Uiterwaal Publications
We report on the ultrafast photoionization of pyridine, pyridazine, pyrimidine, and pyrazine. These four molecules represent a systematic series of perturbations into the structure of a benzene ring which explores the substitution of a C–H entity with a nitrogen atom, creating a heterocyclic structure. Data are recorded under intense-field, single-molecule conditions. The pulses (50 fs, 800 nm) are focused into the molecular vapor, and ion mass spectra are recorded for intensities of ∼1013 W/cm2 to ∼1015 W/cm2. We measure ion yields in the absence of the focal volume effect without the need for deconvolution of …
Magnetic Micro-Structural Uniformity Of Die-Upset Nd-Fe-B Magnets, Yikun Fang, Xiaolu Yin, Rui Zhao, Shah R. Valloppilly, Wei Li, Minggang Zhu, Sy-Hwang Liou
Magnetic Micro-Structural Uniformity Of Die-Upset Nd-Fe-B Magnets, Yikun Fang, Xiaolu Yin, Rui Zhao, Shah R. Valloppilly, Wei Li, Minggang Zhu, Sy-Hwang Liou
Sy-Hwang Liou Publications
Die-upset Nd13.62Fe75.70Co4.45B5.76Ga0.47 magnets have been prepared with height reduction (h) in the range of 60 to 88%. The energy product as high as 50.4 MGOe was obtained in the sample with h~70%. The magnetic domains of the samples are revealed by using magnetic force microscopy (MFM). The average domain widths of the die-upset samples with surface normal parallel (//) and perpendicular (\) to the loading direction are in the range of w//: 0.4-0.6lm; w\: 0.9-3.8 μm, respectively. These interaction domains are formed due to the …