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Articles 31 - 60 of 77
Full-Text Articles in Physics
Hf–Co And Zr–Co Alloys For Rare-Earth-Free Permanent Magnets, Balamurugan Balasubramanian, Bhaskar Das, Wenyong Zhang, Ralph Skomski, David J. Sellmyer
Hf–Co And Zr–Co Alloys For Rare-Earth-Free Permanent Magnets, Balamurugan Balasubramanian, Bhaskar Das, Wenyong Zhang, Ralph Skomski, David J. Sellmyer
David Sellmyer Publications
The structural and magnetic properties of nanostructured Co-rich transition-metal alloys, Co100-xTMx (TM = Hf, Zr and 10 ≤ x ≤ 18), were investigated. The alloys were prepared under nonequilibrium conditions using cluster-deposition and/or melt-spinning methods. The high-anisotropy HfCo7 and Zr2Co11 structures were formed for a rather broad composition region as compared to the equilibrium bulk phase diagrams, and exhibit high Curie temperatures of above 750 K. The composition, crystal structure, particle size, and easy-axis distribution were precisely controlled to achieve a substantial coercivity and magnetization in the nanostructured alloys. This translates into high …
Cms Use Of A Data Federation, Kenneth A. Bloom, C.
Cms Use Of A Data Federation, Kenneth A. Bloom, C.
Kenneth Bloom Publications
CMS is in the process of deploying an Xrootd based infrastructure to facilitate a global data federation. The services of the federation are available to export data from half the physical capacity and the majority of sites are configured to read data over the federation as a back-up. CMS began with a relatively modest set of use-cases for recovery of failed local file opens, debugging and visualization. CMS is finding that the data federation can be used to support small scale analysis and load balancing. Looking forward we see potential in using the federation to provide more flexibility in the …
Temperature Dependence Of Flexoelectric Response In Ferroelectric And Relaxor Polymer Thin Films, Shashi Poddar, Stephen Ducharme
Temperature Dependence Of Flexoelectric Response In Ferroelectric And Relaxor Polymer Thin Films, Shashi Poddar, Stephen Ducharme
Stephen Ducharme Publications
We report the temperature dependence of the flexoelectric response in thin films of both ferroelectric and relaxor forms of vinylidene fluoride polymers. The ferroelectric samples were depoled to minimize piezoelectric response by heating them beyond their Curie temperature and then cooling in zero applied electric field. In both the relaxor ferroelectric polymer and the paraelectric state of the ferroelectric copolymer, the flexoelectric coefficient was proportional to the dielectric constant over a limited range of temperatures, in agreement with general theoretical principles. The enhancements in flexoelectric response were also observed near the Curie transition temperature for the ferroelectric polymer and near …
Ferroelectricity At The Nanoscale, Vladimir M. Fridkin, Stephen Ducharme
Ferroelectricity At The Nanoscale, Vladimir M. Fridkin, Stephen Ducharme
Stephen Ducharme Publications
The properties of ferroelectrics at the nanoscale are reviewed. The term nanoscale is here related to the ferroelectric film thickness (which is by an order of magnitude the size of the critical domain nucleus). The three aspects considered are ferroelectric switching, the scaling of the coercive field, and the bulk photovoltaic effect. While ferroelectricity at the nanoscale has a twenty-year history of study, it is only in the last few years that perovskite ferroelectric films have become a focus of interest.
Wavefront-Correction For Nearly Diffraction Limited Focusing Of Dual-Color Laser Beams To High Intensities, Baozhen Zhao, Jun Zhang, Shouyuan Chen, Cheng Liu, Grigory V. Golovin, Sudeep Banerjee, Kevin J. Brown, Jared Mills, Chad Petersen, Donald Umstadter
Wavefront-Correction For Nearly Diffraction Limited Focusing Of Dual-Color Laser Beams To High Intensities, Baozhen Zhao, Jun Zhang, Shouyuan Chen, Cheng Liu, Grigory V. Golovin, Sudeep Banerjee, Kevin J. Brown, Jared Mills, Chad Petersen, Donald Umstadter
Donald Umstadter Publications
We demonstrate wavefront correction of terawatt-peak-power laser beams at two distinct and well-separated wavelengths. Simultaneous near diffraction-limited focusability is achieved for both the fundamental (800 nm) and second harmonic (400 nm) of Ti:sapphire-amplified laser light. By comparing the relative effectiveness of various correction loops, the optimal ones are found. Simultaneous correction of both beams of different color relies on the linear proportionality between their wavefront aberrations. This method can enable two-color experiments at relativistic intensities.
Generation Of 9 Mev Γ-Rays By All-Laser-Driven Compton Scattering With Second-Harmonic Laser Light, Cheng Liu, Grigory V. Golovin, Shouyuan Chen, Jun Zhang, Baozhen Zhao, Daniel Haden, Sudeep Banerjee, Jack Silano, Hugon Karwowski, Donald Umstadter
Generation Of 9 Mev Γ-Rays By All-Laser-Driven Compton Scattering With Second-Harmonic Laser Light, Cheng Liu, Grigory V. Golovin, Shouyuan Chen, Jun Zhang, Baozhen Zhao, Daniel Haden, Sudeep Banerjee, Jack Silano, Hugon Karwowski, Donald Umstadter
Donald Umstadter Publications
Gamma-ray photons with energy >9 MeV were produced when second-harmonic-generated laser light (3 eV) inverse-Compton-scattered from a counterpropagating relativistic (∼450 MeV) laser-wakefield-accelerated electron beam. Two laser pulses from the same laser system were used: one to accelerate electrons and one to scatter. Since the two pulses play very different roles in the γ-ray generation process, and thus have different requirements, a novel laser system was developed. It separately and independently optimized the optical properties of the two pulses. This approach also mitigated the deleterious effects on beam focusing that generally accompany nonlinear optics at high peak-power levels.
Adaptive-Feedback Spectral-Phase Control For Interactions With Transform-Limited Ultrashort High-Power Laser Pulses, Cheng Liu, Jun Zhang, Shouyuan Chen, Grigory V. Golovin, Sudeep Banerjee, Baozhen Zhao, Nathan D. Powers, Isaac Ghebregziabher, Donald Umstadter
Adaptive-Feedback Spectral-Phase Control For Interactions With Transform-Limited Ultrashort High-Power Laser Pulses, Cheng Liu, Jun Zhang, Shouyuan Chen, Grigory V. Golovin, Sudeep Banerjee, Baozhen Zhao, Nathan D. Powers, Isaac Ghebregziabher, Donald Umstadter
Donald Umstadter Publications
laser in vacuum. The spectral-phase distortion induced by the dispersion mismatching between the stretcher, compressor, and dispersive materials was fully compensated for by means of an adaptive closed-loop. The coherent temporal contrast on the sub-picosecond time scale was two orders of magnitude higher than that without adaptive control. This novel phase control capability enabled the experimental study of the dependence of laser wakefield acceleration on the spectral phase of intense laser light
Temporary Anion States Of Three Herbicide Families, Adam M. Scheer, Kayvan Aflatooni, Gordon A. Gallup, Paul Burrow
Temporary Anion States Of Three Herbicide Families, Adam M. Scheer, Kayvan Aflatooni, Gordon A. Gallup, Paul Burrow
Paul Burrow Publications
Electron scattering studies are used to locate the energies of temporary negative ion states of three chloro-substituted molecular families of herbicidal importance: salicylic and phenoxyacetic acids and acetamides. The correlation between these energies and the computed virtual orbital energies of the compounds is examined and used to put the latter on an absolute energy scale. Such scaling of orbital energies permits the anion states of other members of these families, for which experimental data may not be available, to be estimated from the calculated orbital energies. Studies of electron reduction rates often rely on calculated LUMO energies as molecular descriptors. …
Organic Ferroelectric Evaporator With Substrate Cooling And In Situ Transport Capabilities, Keith Foreman, C. Labedz, M. Shearer, Shireen Adenwalla
Organic Ferroelectric Evaporator With Substrate Cooling And In Situ Transport Capabilities, Keith Foreman, C. Labedz, M. Shearer, Shireen Adenwalla
Shireen Adenwalla Papers
We report on the design, operation, and performance of a thermal evaporation chamber capable of evaporating organic thin films. Organic thin films are employed in a diverse range of devices and can provide insight into fundamental physical phenomena. However, growing organic thin films is often challenging and requires very specific deposition parameters. The chamber presented here is capable of cooling sample substrates to temperatures below 130 K and allows for the detachment of the sample from the cooling stage and in situ transport. This permits the use of multiple deposition techniques in separate, but connected, deposition chambers without breaking vacuum …
Practical Aspects Of Modern And Future Permanent Magnets, R.W. Mccallum, L. H. Lewis, Ralph Skomski, M. J. Kramer, I. E. Anderson
Practical Aspects Of Modern And Future Permanent Magnets, R.W. Mccallum, L. H. Lewis, Ralph Skomski, M. J. Kramer, I. E. Anderson
Ralph Skomski Publications
The mandate to reduce greenhouse gases will require highly efficient electric machines for both power generation and traction motor applications. Although permanent magnet electric machines utilizing Nd2Fe14B-based magnets provide obvious power-to-weight advantages over induction machines, the limited availability and high price of the rare earth (RE) metals make these machines less favorable. Of particular concern is the cost and supply criticality of Dy, a key RE element that is required to improve the high-temperature performance of Nd-based magnetic alloys for use in generators and traction motors. Alternatives to RE-based alloys do exist, but they currently lack the energy density necessary …
Rare Earth Dopant (Nd, Gd, Dy, And Er) Hybridization In Lithium Tetraborate, Tony D. Kelly, James C. Petrosky, John W. Mcclory, Volodymyr T. Adamiv, Yaroslav V. Burak, Bohdan V. Padlyak, Ihor M. Teslyuk, Ning Liu, Lu Wang, Wai-Ning Mei, Peter A. Dowben
Rare Earth Dopant (Nd, Gd, Dy, And Er) Hybridization In Lithium Tetraborate, Tony D. Kelly, James C. Petrosky, John W. Mcclory, Volodymyr T. Adamiv, Yaroslav V. Burak, Bohdan V. Padlyak, Ihor M. Teslyuk, Ning Liu, Lu Wang, Wai-Ning Mei, Peter A. Dowben
Peter Dowben Publications
The four dopants (Nd, Gd, Dy, and Er) substitutionally occupy the Li+ sites in lithium tetra borate (Li2B407: RE) glasses as determined by analysis of the extended X-ray absorption fine structure. The dopants are coordinated by 6-8 oxygen at a distance of 2.3 to 2.5 A. depending on the rare earth. The inverse relationship between the RE-O coordination distance and rare earth (RE) atomic number is consistent with the expected lanthanide atomic radial contraction with increased atomic number. Through analysis of the X-ray absorption near edge structure, the rare earth dopants adopt the RE …
Spin Polarization Asymmetry At The Surface Of Chromia, Shi Cao, Xin Zhang, Ning Wu, A T. N'Diaye, G Chen, A K. Schmid, Xumin Chen, W Echtenkamp, Axel Enders, Christian Binek, Peter A. Dowben
Spin Polarization Asymmetry At The Surface Of Chromia, Shi Cao, Xin Zhang, Ning Wu, A T. N'Diaye, G Chen, A K. Schmid, Xumin Chen, W Echtenkamp, Axel Enders, Christian Binek, Peter A. Dowben
Peter Dowben Publications
We demonstrate boundary spin polarization at the surface of a Cr2O3 single crystal using spin-polarized low-energy electron microscopy (SPLEEM), complementing prior spin polarized photoemission, spin polarized inverse photoemission, and x-ray magnetic circular dichroism photoemission electron microscopy measurements. This work shows that placing a Cr2O3 single crystal into a single domain state will result in net Cr2O3 spin polarization at the boundary, even in the presence of a gold overlayer. There are indications that the SPLEEM contrast for the two polarization states may be different, consistent with scanning tunneling microscopy spectroscopy results …
Ferroelectric Switching In Epitaxial Gete Films, A. V. Kolobov, D. J. Kim, A. Giussani, P. Fons, J. Tominaga, R. Calarco, Alexei Gruverman
Ferroelectric Switching In Epitaxial Gete Films, A. V. Kolobov, D. J. Kim, A. Giussani, P. Fons, J. Tominaga, R. Calarco, Alexei Gruverman
Alexei Gruverman Publications
In this paper, using a resonance-enhanced piezoresponse force microscopy approach supported by density functional theory computer simulations, we have demonstrated the ferroelectric switching in epitaxial GeTe films. It has been shown that in films with thickness on the order of several nanometers reversible reorientation of polarization occurs due to swapping of the shorter and longer Ge-Te bonds in the interior of the material. It is also hinted that for ultra thin films consisting of just several atomic layers weakly bonded to the substrate, ferroelectric switching may proceed through exchange of Ge and Te planes within individual GeTe layers.
Chirally Sensitive Electron-Induced Molecular Breakup And The Vester-Ulbricht Hypothesis, J. M. Dreiling, Timothy J. Gay
Chirally Sensitive Electron-Induced Molecular Breakup And The Vester-Ulbricht Hypothesis, J. M. Dreiling, Timothy J. Gay
Timothy J. Gay Publications
We have studied dissociative electron attachment in sub-eV collisions between longitudinally polarized electrons and chiral bromocamphor molecules. For a given target enantiomer, the dissociative Br anion production depends on the helicity of the incident electrons, with an asymmetry that depends on the electron energy and is of order 3 × 10−4. The existence of chiral sensitivity in a well-defined molecular breakup reaction demonstrates the viability of the Vester-Ulbrict hypothesis, namely, that the longitudinal polarization of cosmic beta radiation was responsible for the origins of biological homochirality.
The Spin State Of A Molecular Adsorbate Driven By The Ferroelectric Substrate Polarization†, Xin Zhang, Tatiana Palamarciuc, Jean-François Létard, Patrick Rosa, Eduardo Vega Lozada, Fernand Torres, Luis G. Rosa, Bernard Doudin, Peter A. Dowben
The Spin State Of A Molecular Adsorbate Driven By The Ferroelectric Substrate Polarization†, Xin Zhang, Tatiana Palamarciuc, Jean-François Létard, Patrick Rosa, Eduardo Vega Lozada, Fernand Torres, Luis G. Rosa, Bernard Doudin, Peter A. Dowben
Peter Dowben Publications
The spin state of [Fe(H2B(pz)2)2(bipy)] thin films is mediated by changes in the electric field at the interface of organic ferroelectric polyvinylidene fluoride with trifluoroethylene (PVDF–TrFE). Signatures of the molecular crossover transition are evident in changes in the unoccupied states and the related shift from diamagnetic to paramagnetic characteristics. This may point the way to the molecular magneto-electric effect on devices.
Increasing The Neel Temperature Of Magnetoelectric Chromia For Voltage-Controlled Spintronics, M Street, W Echtenkamp, Takashi Komesu, Shi Cao, Peter A. Dowben, Christian Binek
Increasing The Neel Temperature Of Magnetoelectric Chromia For Voltage-Controlled Spintronics, M Street, W Echtenkamp, Takashi Komesu, Shi Cao, Peter A. Dowben, Christian Binek
Peter Dowben Publications
Boron doped chromia (Cr2O3) thin films with substitutional doping levels between zero and 3% are grown using pulsed laser deposition in borane background gases. Magnetometry reveals a tunable increase in the Neel temperature of the (0001) textured Cr2BxO3-x thin films at a rate of about 10% with 1% oxygen site substitution preserving a net boundary magnetization. Spin resolved inverse photoemission measured after magnetoelectric annealing in subsequently reversed electric fields evidences voltage-controlled reversal of boundary magnetization and thus magnetoelectricity of Cr2BxO3-x. Conservation of magnetoelectricity far above …
Occupied And Unoccupied Electronic Structure Of Na Doped Mos2(0001), Takashi Komesu, Duy Le, Xin Zhang, Quan Ma, Eike F. Schwier, Yohei Kojima, Mintian Zheng, Hideaki Iwasawa, Kenya Shimada, Masaki Taniguchi, Ludwig Bartels, Talat S. Rahman, Peter A. Dowben
Occupied And Unoccupied Electronic Structure Of Na Doped Mos2(0001), Takashi Komesu, Duy Le, Xin Zhang, Quan Ma, Eike F. Schwier, Yohei Kojima, Mintian Zheng, Hideaki Iwasawa, Kenya Shimada, Masaki Taniguchi, Ludwig Bartels, Talat S. Rahman, Peter A. Dowben
Peter Dowben Publications
The influence of sodium on the band structure of MoS2(0001) and the comparison of the experimental band dispersion with density functional theory show excellent agreement for the occupied states (angle-resolved photoemission) and qualitative agreement for the unoccupied states (inverse photoemission spectroscopy). Na-adsorption leads to charge transfer to the MoS2 surface causing an effect similar to n-type doping of a semiconductor. The MoS2 occupied valence band structure shifts rigidly to greater binding with little change in the occupied state dispersion. Likewise, the unoccupied states shift downward, approaching the Fermi level, yet the amount of the shift for …
The Chromium Site In Doped Glassy Lithium Tetraborate, T D. Kelly, E Echeverria, Sumit Beniwal, V T. Adamiv, Ya V. Burak, Axel Enders, J. C. Petrosky, J W. Mcclory, Peter A. Dowben
The Chromium Site In Doped Glassy Lithium Tetraborate, T D. Kelly, E Echeverria, Sumit Beniwal, V T. Adamiv, Ya V. Burak, Axel Enders, J. C. Petrosky, J W. Mcclory, Peter A. Dowben
Peter Dowben Publications
Using extended X-ray absorption fine structure (EXAFS) spectroscopy, we find that Cr substitutes primarily in the Liþ site as a dopant in lithium tetraborate Li2B4O7 glasses, in this case 98.4Li2B4O7e1.6Cr2O3 or nominally Li1.98Cr0.025B4O7. This strong preference for a single site is nonetheless accompanied by site distortions and some site disorder, helping explain the optical properties of chromium doped Li2B4O7 glasses. The resulting O coordination shell has a contraction of the Cr-O …
Sublattice-Induced Symmetry Breaking And Bandgap Formation In Graphene, Ralph A. Skomski, Peter A. Dowben, M Sky Driver, Jeffery A. Kelber
Sublattice-Induced Symmetry Breaking And Bandgap Formation In Graphene, Ralph A. Skomski, Peter A. Dowben, M Sky Driver, Jeffery A. Kelber
Peter Dowben Publications
A reduction of symmetry from C6v to C3v leads to the opening of a band gap in the otherwise gapless semiconductor graphene. Simple models provide a fairly complete picture of this mechanism for opening a band gap and in fact can be discussed in terms of the tight-binding approximation, accurately resolving the wave-vector space to a very high accuracy. This picture is consistent with experiments that yield a band gap due to A and B graphene-site symmetry breaking due to substrate interactions.
The Unoccupied Electronic Structure Characterization Of Hydrothermally Grown Tho2 Single Crystals, T D. Kelly, J C. Petrosky, D Turner, J W. Mcclory, J M. Mann, J W. Kolis, Xin Zhang, Peter A. Dowben
The Unoccupied Electronic Structure Characterization Of Hydrothermally Grown Tho2 Single Crystals, T D. Kelly, J C. Petrosky, D Turner, J W. Mcclory, J M. Mann, J W. Kolis, Xin Zhang, Peter A. Dowben
Peter Dowben Publications
Single crystals of thorium dioxide ThO2, grown by the hydrothermal growth technique, have been investigated by ultraviolet photoemission spectroscopy (UPS), inverse photoemission spectroscopy (IPES), and L3, M3, M4, and M5 X-ray absorption near edge spectroscopy (XANES). The experimental band gap for large single crystals has been determined to be 6 eV to 7 eV, from UPS and IPES, in line with expectations. The combined UPS and IPES, place the Fermi level near the conduction band minimum, making these crystals n-type, with extensive band tailing, suggesting an optical gap in the region …
The Ferroelectricity At The Nanoscale, Vladimir M. Fridkin, Stephen Ducharme
The Ferroelectricity At The Nanoscale, Vladimir M. Fridkin, Stephen Ducharme
Stephen Ducharme Publications
The review of ferroelectric properties at the nanoscale is presented. Determining the nanoscale, authors bear in mind the film thickness equal by the order of value to the size of critical domain nucleus. Three phenomena are considered: ferroelectric switching, scaling of coercive field and bulk photovoltaic effect. The investigation of ferroelectricity at the nanoscale started 20 years ago. The nanoscaled ferroelectricics with perovskite structure came to be considered only the last few years.
Laboratory Manual For Physics Of Lasers And Modern Optics, 13th Ed, Stephen Ducharme
Laboratory Manual For Physics Of Lasers And Modern Optics, 13th Ed, Stephen Ducharme
Stephen Ducharme Publications
You will encounter challenging puzzles and explore new and exciting physical phenomena. You will be provided with sufficient tools, guidance and other resources, but what you learn depends on your inquisitiveness and creativity. This laboratory course is designed to serve two purposes: 1) To explore a variety of physical principles using the fascinating and diverse behavior of light. 2) To learn some of the principles behind the pervasive and expanding area of optical and laser technology. This course is suitable for students of science, life sciences, and engineering, or any student who is curious about light. The prerequisites are the …
Orthorhombic Zr2Co11 Phase Revisited, Xingzhong Li, Wenyong Zhang, David J. Sellmyer, X Zhao, M C. Nguyen, C Z. Wang, K M. Ho
Orthorhombic Zr2Co11 Phase Revisited, Xingzhong Li, Wenyong Zhang, David J. Sellmyer, X Zhao, M C. Nguyen, C Z. Wang, K M. Ho
David Sellmyer Publications
The structure of the orthorhombic Zr2Co11 phase was revisited in the present work. Selected-area electron diffraction (SAED) and high-resolution electron microscopy (HREM) techniques were used to investigate the structure. They show the orthorhombic Zr2Co11 phase has a 1-D incommensurate modulated structure. The structure can be approximately described as a B-centered orthorhombic lattice. The lattice parameters of the orthorhombic Zr2Co11 phase have been determined by a tilt series of SAED patterns. A hexagonal network with a modulation wave has been observed in the HREM image and the hexagonal motif is considered as …
Adjusting Magnetic Nanostructures For High-Performance Magnetic Sensors, Xiaolu Yin, Ralph A. Skomski, David J. Sellmyer, Sy-Hwang Liou, Stephen E. Russek, Eric R. Evarts, John Moreland, A S. Edelstein, L Yuan, M L. Yan, J Shen
Adjusting Magnetic Nanostructures For High-Performance Magnetic Sensors, Xiaolu Yin, Ralph A. Skomski, David J. Sellmyer, Sy-Hwang Liou, Stephen E. Russek, Eric R. Evarts, John Moreland, A S. Edelstein, L Yuan, M L. Yan, J Shen
David Sellmyer Publications
The magnetic properties of the soft ferromagnetic layer in magnetic tunnel junctions are one of key factors to determine the performance of magnetoresistance sensors. We use a three-step orthogonal annealing procedure to modify the nanostructures of the free layer in the magnetic tunnel junction to control features such as magnetization reversal, coercivity, exchange field, and tunnel magnetoresistance ratio. We present a sensor with an improved sensitivity as high as 3944%/mT. This magnetic sensor only dissipates 200 lW of power while operating under an applied voltage of 1V.
Development And Intrinsic Properties Of Hexagonal Ferromagnetic (Zr,Ti)Fe2, Wenyong Zhang, Xingzhong Li, Shah R. Valloppilly, Ralph A. Skomski, Jeffrey E. Shield, David J. Sellmyer
Development And Intrinsic Properties Of Hexagonal Ferromagnetic (Zr,Ti)Fe2, Wenyong Zhang, Xingzhong Li, Shah R. Valloppilly, Ralph A. Skomski, Jeffrey E. Shield, David J. Sellmyer
David Sellmyer Publications
Nanocrystalline Ti0.75Zr0.25Fe2+x (x=0-0.4) and Ti0.75-yByZr0.25Fe2.4 (y=0-0.35) with high saturation magnetization have been fabricated by the melt-spinning technique. Nanocrystalline Ti0.75Zr0.25Fe2+x consists of the hexagonal C14 Laves phase (Ti,Zr)Fe2. Fe addition decreases the lattice parameter a and shrinks the cell volume. The antiferromagnetic Fe-Fe interactions may decrease with the increase of x, leading to a significant enhancement of saturation polarization (Js) and Curie temperature (Tc). The magnetocrystalline anisotropy constant K also increases with increasing x. Excessive Fe addition (x>0.25) may induce structural …
Effect Of Quench Rate On Nanostructure And Magnetic Properties Of Prco5, Wenyong Zhang, Ralph Skomski, Xingzhong Li, Shah R. Valloppilly, Jeffrey E. Shield, David J. Sellmyer
Effect Of Quench Rate On Nanostructure And Magnetic Properties Of Prco5, Wenyong Zhang, Ralph Skomski, Xingzhong Li, Shah R. Valloppilly, Jeffrey E. Shield, David J. Sellmyer
David Sellmyer Publications
The effect of quench rate on nanostructure and magnetic properties of PrCo5 alloy has been investigated. The increase of quench rate through wheel speed in melt spinning suppresses the formation of the secondary Pr2Co17 and Pr5Co19 phases with low magnetocrystalline anisotropy field and refines the nanostructure. This significantly improves the coercivity, remanence, and energy product. For example, increasing the wheel speed from 30 m/s to 70 m/s increases the coercivity and energy product from 3.2 kOe and 4.0 MGOe to 10.3 kOe and 13.7 MGOe, respectively. The magnetic hardening mechanism appears to be …
Exploring The Structural Complexity Of Intermetallic Compounds By An Adaptive Genetic Algorithm, X Zhao, M C. Nguyen, Wenyong Zhang, C Z. Wang, Matthew J. Kramer, David J. Sellmyer, Xingzhong Li, F Zhang, Liqin Ke, Vladimir P. Antropov, K M. Ho
Exploring The Structural Complexity Of Intermetallic Compounds By An Adaptive Genetic Algorithm, X Zhao, M C. Nguyen, Wenyong Zhang, C Z. Wang, Matthew J. Kramer, David J. Sellmyer, Xingzhong Li, F Zhang, Liqin Ke, Vladimir P. Antropov, K M. Ho
David Sellmyer Publications
Solving the crystal structures of novel phases with nanoscale dimensions resulting from rapid quenching is difficult due to disorder and competing polymorphic phases. Advances in computer speed and algorithm sophistication have now made it feasible to predict the crystal structure of an unknown phase without any assumptions on the Bravais lattice type, atom basis, or unit cell dimensions, providing a novel approach to aid experiments in exploring complex materials with nanoscale grains. This approach is demonstrated by solving a long-standing puzzle in the complex crystal structures of the orthorhombic, rhombohedral, and hexagonal polymorphs close to the Zr2Co11 …
Magnetic Hardening Of Zr2Co11:(Ti, Si) Nanomaterials, Wenyong Zhang, Shah R. Valloppilly, Xingzhong Li, Yi Liu, Steven A. Michalski, T A. George, Ralph A. Skomski, David J. Sellmyer
Magnetic Hardening Of Zr2Co11:(Ti, Si) Nanomaterials, Wenyong Zhang, Shah R. Valloppilly, Xingzhong Li, Yi Liu, Steven A. Michalski, T A. George, Ralph A. Skomski, David J. Sellmyer
David Sellmyer Publications
The role of Ti and Si additions in the magnetic hardening of rapidly quenched Zr2Co11-based nano-materials has been investigated. Nanocrystalline Zr17–xTixCo83 and Zr18Co82–ySiy are mainly composed of rhombohedral Zr2Co11 and a small amount of orthorhombic Zr2Co11, hcp Co, and cubic Zr6Co23. Ti addition decreases the mean grain size of the magnetic phases, and thus increases coercivity and energy product from 1.6 kOe and 1.9 MGOe for x = 0 to 2.6 kOe and 3.9 MGOe …
Permanent Magnetism Of Intermetallic Compounds Between Light And Heavy Transition-Metal Elements, P Kumar, Arti Kashyap, Balamurugan Balamurugan, Jeffrey E. Shield, David J. Sellmyer, Ralph Skomski
Permanent Magnetism Of Intermetallic Compounds Between Light And Heavy Transition-Metal Elements, P Kumar, Arti Kashyap, Balamurugan Balamurugan, Jeffrey E. Shield, David J. Sellmyer, Ralph Skomski
David Sellmyer Publications
First principle calculations are used to investigate the intrinsic magnetic properties of intermetallic alloys of the type XMn, where X is a 4d or 5d element and M is Fe or Co. Emphasis is on the hexagonal C14 Laves-phase 1:2 and 1:5 alloys, the latter crystallizing in the CaCu5 structure. These series are of interest in permanent magnetism from fundamental and practical viewpoints, respectively. In the former, the unit cells form a prototypical motif where a heavy atom with high spin-orbit coupling and magnetocrystalline anisotropy is surrounded by many somewhat smaller M atoms with high magnetization, …
Direct Chemical Synthesis Of L10-Feptau Nanoparticles With High Coercivity, Yongsheng Yu, Pinaki Mukherjee, Yuan Tian, Xingzhong Li, David J. Sellmyer
Direct Chemical Synthesis Of L10-Feptau Nanoparticles With High Coercivity, Yongsheng Yu, Pinaki Mukherjee, Yuan Tian, Xingzhong Li, David J. Sellmyer
David Sellmyer Publications
We report a facile synthesis of hard magnetic L10-FePtAu nanoparticles by coreduction of Fe(acac)3, Pt(acac)2 (acac = acetylacetonate), and gold acetate in oleylamine. In the current reaction condition, NP sizes are controlled to be 5.5 to 11.0 nm by changing the amount of Au doping. When the Au composition in the NPs is higher than 14%, the hard magnetic NPs are directly obtained without any annealing. The highest coercivity of 12.15 kOe at room temperature could be achieved for the NPs with 32% Au doping, which is much higher than the coercivities reported by the …