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Articles 1 - 23 of 23
Full-Text Articles in Physics
Direct Observation Of The Magnetic Anisotropy Of An Fe (Ii) Spin Crossover Molecular Thin Film, Ashley S. Dale, Saeed Yazdani, Thilini K. Ekanayaka, Esha Mishra, Yuchen Hu, Peter A. Dowben, John W. Freeland, Jian Zhang, Ruihua Cheng
Direct Observation Of The Magnetic Anisotropy Of An Fe (Ii) Spin Crossover Molecular Thin Film, Ashley S. Dale, Saeed Yazdani, Thilini K. Ekanayaka, Esha Mishra, Yuchen Hu, Peter A. Dowben, John W. Freeland, Jian Zhang, Ruihua Cheng
Department of Physics and Astronomy: Faculty Publications
Spin crossover molecules are a promising candidate for molecular spintronics that aim for ultrafast and low-power devices for data storage and magnetic and information sensing. The rapid spin state transition is best controlled by non-thermal methods including magnetic field. Unfortunately, the magnetic field normally required to switch the spin state is normally high (~30 T), which calls for better understanding of the fundamental mechanism. In this work, we provide clear evidence of magnetic anisotropy in the local orbital moment of a molecular thin film based on spin crossover complex [Fe(H2B(pz)2)2(bipy)] (pz = pyrazol−1−yl, bipy …
Probing Exchange Bias At The Surface Of A Doped Ferrimagnetic Insulator, Yang Wang, Xiao Wang, Andy T. Clark, Hang Chen, Xuemei Cheng, John W. Freeland, John Q. Xiao
Probing Exchange Bias At The Surface Of A Doped Ferrimagnetic Insulator, Yang Wang, Xiao Wang, Andy T. Clark, Hang Chen, Xuemei Cheng, John W. Freeland, John Q. Xiao
Physics Faculty Research and Scholarship
With the realization of stress-induced perpendicular magnetic anisotropy, efficient spin-orbit torque switching, and room temperature topological Hall effect, interest in rare earth iron garnets has been revived in recent years for their potential in spintronic applications. In this study, we investigate the magnetic properties of micrometer-thick Bi and Ga substituted thulium iron garnets (BiGa:TmIG) grown by the liquid-phase epitaxy method. Above the magnetization compensation (MC) temperature, anomalous triple hysteresis is observed in BiGa:TmIG/Pt heterostructures by anomalous Hall effect measurements. X-ray magnetic circular dichroism and energy dispersive spectroscopy measurements reveal its origin as an internal exchange bias (EB) effect arising from …
Effect Of Strain On Charge Density Wave Order In The Holstein Model, Benjami Cohen-Stead, Natanael Costa, Ehsan Khatami, Richard Scalettar
Effect Of Strain On Charge Density Wave Order In The Holstein Model, Benjami Cohen-Stead, Natanael Costa, Ehsan Khatami, Richard Scalettar
Faculty Publications
We investigate charge ordering in the Holstein model in the presence of anisotropic hopping, tx,ty=1-δ,1+δ, as a model of the effect of strain on charge-density-wave (CDW) materials. Using quantum Monte Carlo simulations, we show that the CDW transition temperature is relatively insensitive to moderate anisotropy δ 0.3, but begins to decrease more rapidly at δ 0.4. However, the density correlations, as well as the kinetic energies parallel and perpendicular to the compressional axis, change significantly for moderate δ. Accompanying mean-field theory calculations show a similar qualitative structure, with the transition temperature relatively constant at small δ, and a more rapid …
Dielectric Function Tensor (1.5 Ev To 9.0 Ev), Anisotropy, And Band To Band Transitions Of Monoclinic Β-(AlXGa1–X)2O3 (X ≤ 0.21) Films, Matthew Hilfiker, Ufuk Kilic, Alyssa Mock, Vanya Darakchieva, Sean Knight, Rafal Korlacki, Akhil Mauze, Yuewei Zhang, James Speck, Mathias Schubert
Dielectric Function Tensor (1.5 Ev To 9.0 Ev), Anisotropy, And Band To Band Transitions Of Monoclinic Β-(AlXGa1–X)2O3 (X ≤ 0.21) Films, Matthew Hilfiker, Ufuk Kilic, Alyssa Mock, Vanya Darakchieva, Sean Knight, Rafal Korlacki, Akhil Mauze, Yuewei Zhang, James Speck, Mathias Schubert
Department of Electrical and Computer Engineering: Faculty Publications
A set of monoclinic β-(AlxGa1–x)2O3 films coherently grown by plasma-assisted molecular beam epitaxy onto (010)-oriented β-Ga2O3 substrates for compositions x ≤ 0.21 is investigated by generalized spectroscopic ellipsometry at room temperature in the spectral range of 1.5 eV–9.0 eV. We present the composition dependence of the excitonic and band to band transition energy parameters using a previously described eigendielectric summation approach for β-Ga2O3 from the study by Mock et al. All energies shift to a shorter wavelength with the increasing Al content in …
Generalized Ellipsometry On Complex Nanostructures And Low-Symmetry Materials, Alyssa Mock
Generalized Ellipsometry On Complex Nanostructures And Low-Symmetry Materials, Alyssa Mock
Department of Electrical and Computer Engineering: Dissertations, Theses, and Student Research
In this thesis, complex anisotropic materials are investigated and characterized by generalized ellipsometry. In recent years, anisotropic materials have gained considerable interest for novel applications in electronic and optoelectronic devices, mostly due to unique properties that originate from reduced crystal symmetry. Examples include white solid-state lighting devices which have become ubiquitous just recently, and the emergence of high-power, high-voltage electronic transistors and switches in all-electric vehicles. The incorporation of single crystalline material with low crystal symmetry into novel device structures requires reconsideration of existing optical characterization approaches. Here, the generalized ellipsometry concept is extended to include applications for materials with …
Tuning The Effective Anisotropy In A Voltage-Susceptible Exchange-Bias Heterosystem, Will Echtenkamp, Mike Street, Ather Mahmood, Christian Binek
Tuning The Effective Anisotropy In A Voltage-Susceptible Exchange-Bias Heterosystem, Will Echtenkamp, Mike Street, Ather Mahmood, Christian Binek
Christian Binek Publications
Voltage- and temperature-tuned ferromagnetic hysteresis is investigated by a superconducting quantum-interference device and Kerr magnetometry in a thin-film heterostructure of a perpendicular anisotropic Co/Pd ferromagnet exchange coupled to the magnetoelectric antiferromagnet Cr2O3. An abrupt disappearance of exchange bias with a simultaneous more than twofold increase in coercivity is observed and interpreted as a competition between the effective anisotropy of Cr2O3 and the exchange-coupling energy between boundary magnetization and the adjacent ferromagnet. The effective anisotropy energy is given by the intrinsic anisotropy energy density multiplied by the effective volume separated from the bulk through …
Azimuthal Anisotropy In U+U And Au+Au Collisions At Rhic, James K. Adkins, Renee H. Fatemi, Suvarna Ramachandran, L. Adamczyk, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, I. Alekseev, J. Alford, A. Aparin, D. Arkhipkin, E. C. Aschenauer, G. S. Averichev
Azimuthal Anisotropy In U+U And Au+Au Collisions At Rhic, James K. Adkins, Renee H. Fatemi, Suvarna Ramachandran, L. Adamczyk, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, I. Alekseev, J. Alford, A. Aparin, D. Arkhipkin, E. C. Aschenauer, G. S. Averichev
Physics and Astronomy Faculty Publications
Collisions between prolate uranium nuclei are used to study how particle production and azimuthal anisotropies depend on initial geometry in heavy-ion collisions. We report the two- and four-particle cumulants, v2{2} and v2{4}, for charged hadrons from U+U collisions at √sNN=193 GeV and Au+Au collisions at √sNN=200 GeV. Nearly fully overlapping collisions are selected based on the energy deposited by spectators in zero degree calorimeters (ZDCs). Within this sample, the observed dependence of v2{2} on multiplicity demonstrates that ZDC information combined with multiplicity can preferentially select different overlap configurations …
Room Temperature Optical Anisotropy Of A Lamno3 Thin-Film Induced By Ultra-Short Pulse Laser, Purevdorj Munkhbaatar, Zsolt Marton, Baatarchuluun Tsermaa, Woo Seok Choi, Sung S. Ambrose Seo, Jin Seung Kim, Naoyuki Nakagawa, Harold Y. Hwang, Ho Nyung Lee, Kim Myung-Whun
Room Temperature Optical Anisotropy Of A Lamno3 Thin-Film Induced By Ultra-Short Pulse Laser, Purevdorj Munkhbaatar, Zsolt Marton, Baatarchuluun Tsermaa, Woo Seok Choi, Sung S. Ambrose Seo, Jin Seung Kim, Naoyuki Nakagawa, Harold Y. Hwang, Ho Nyung Lee, Kim Myung-Whun
Physics and Astronomy Faculty Publications
We observed ultra-short laser pulse-induced transient optical anisotropy in a LaMnO3 thin film. The anisotropy was induced by laser pulse irradiation with a fluence of less than 0.1 mJ/cm2 at room temperature. The transmittance and reflectance showed strong dependence on the polarization states of the pulses. For parallel and perpendicular polarization states, there exists a difference of approximately 0.2% for transmittance and 0.05% for reflectance at 0.3 ps after the irradiation with a pump pulse, respectively. The theoretical values for optical transmittance and reflectance with an assumption of an orbital ordering of 3d eg electrons in …
Dielectron Azimuthal Anisotropy At Mid-Rapidity In Au + Au Collisions At √SNn=200 Gev, J. Kevin Adkins, Renee Fatemi, Suvarna Ramachandran, G. Webb, L. Adamczyk, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, I. Alekseev, J. Alford, C. D. Anson, A. Aparin, D. Arkhipkin
Dielectron Azimuthal Anisotropy At Mid-Rapidity In Au + Au Collisions At √SNn=200 Gev, J. Kevin Adkins, Renee Fatemi, Suvarna Ramachandran, G. Webb, L. Adamczyk, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, I. Alekseev, J. Alford, C. D. Anson, A. Aparin, D. Arkhipkin
Physics and Astronomy Faculty Publications
We report on the first measurement of the azimuthal anisotropy (v2) of dielectrons (e+e− pairs) at mid-rapidity from √SNN=200 GeV Au + Au collisions with the STAR detector at the Relativistic Heavy Ion Collider (RHIC), presented as a function of transverse momentum (pT) for different invariant-mass regions. In the mass region Meec2 the dielectron v2 measurements are found to be consistent with expectations from π0, η, ω, and ϕ decay contributions. In the mass region 1.1<Mee<2.9GeV/c …
Particle Moment Canting In Cofe2o4 Nanoparticles, K. Hasz, Yumi Ijiri, Kathryn L. Krycka, Julie A. Borchers, R.A. Booth, S. Oberdick, S.A. Majetich
Particle Moment Canting In Cofe2o4 Nanoparticles, K. Hasz, Yumi Ijiri, Kathryn L. Krycka, Julie A. Borchers, R.A. Booth, S. Oberdick, S.A. Majetich
Faculty & Staff Scholarship
Polarization-analyzed small-angle neutron scattering methods are used to determine the spin morphology in high crystalline anisotropy, 11 nm diameter CoFe2O4 nanoparticle assemblies with randomly oriented easy axes. In moderate to high magnetic fields, the nanoparticles adopt a uniformly canted structure, rather than forming domains, shells, or other arrangements. The observed canting angles agree quantitatively with those predicted from an energy model dominated by Zeeman and anisotropy competition, with implications for the technological use of such nanoparticles.
Network-Based Assessments Of Percolation-Induced Current Distributions In Sheared Rod Macromolecular Dispersions, Feng Shi, Simi Wang, M. Gregory Forest, Peter J. Mucha, Ruhai Zhou
Network-Based Assessments Of Percolation-Induced Current Distributions In Sheared Rod Macromolecular Dispersions, Feng Shi, Simi Wang, M. Gregory Forest, Peter J. Mucha, Ruhai Zhou
Mathematics & Statistics Faculty Publications
Conducting high-aspect-ratio rods with 1-10 nm-scale diameters dispersed in poorly conducting matrices at extremely low, O(1%), volume fractions induce dramatic gains in bulk conductivity at rod percolation threshold. Experimentally [Nan, Shen, and Ma, Annu. Rev. Mater. Res., 40 (2010), pp. 131-151], bulk conductivity abandons the prepercolation, linear scaling with volume fraction that follows from homogenization theory [Zheng et al., Adv. Funct. Mater., 15 (2005), pp. 627-638], and then postpercolation jumps orders of magnitude to approach that of the pure rod macromolecular phase as predicted by classical percolation theory [Stauffer and Aharony, Introduction to Percolation Theory, CRC …
Imaging The Anisotropic Nonlinear Meissner Effect In Nodal Yba ₂Cu₃O7-Δ Thin-Film Superconductors, Alexander P. Zhuravel, Behnood G. Ghamsari, Cihan Kurter, Philipp Jung, Stephen K. Remillard, John A. Abrahams, Alexander V. Lukashenko, Alexey V. Ustinov, Steven Mark Anlage
Imaging The Anisotropic Nonlinear Meissner Effect In Nodal Yba ₂Cu₃O7-Δ Thin-Film Superconductors, Alexander P. Zhuravel, Behnood G. Ghamsari, Cihan Kurter, Philipp Jung, Stephen K. Remillard, John A. Abrahams, Alexander V. Lukashenko, Alexey V. Ustinov, Steven Mark Anlage
Physics Faculty Research & Creative Works
We have directly imaged the anisotropic nonlinear Meissner effect in an unconventional superconductor through the nonlinear electrodynamic response of both (bulk) gap nodes and (surface) Andreev bound states. A superconducting thin film is patterned into a compact self-resonant spiral structure, excited near resonance in the radio-frequency range, and scanned with a focused laser beam perturbation. At low temperatures, direction-dependent nonlinearities in the reactive and resistive properties of the resonator create photoresponse that maps out the directions of nodes, or of bound states associated with these nodes, on the Fermi surface of the superconductor. The method is demonstrated on the nodal …
Acyl-Chain Mismatch Driven Superlattice Arrangements In Dppc/Dlpc/Cholesterol Bilayers, Brian Cannon, Anthony Lewis, Pentti Somerharju, Jorma Virtanen, Juyang Huang, Kwan H. Cheng
Acyl-Chain Mismatch Driven Superlattice Arrangements In Dppc/Dlpc/Cholesterol Bilayers, Brian Cannon, Anthony Lewis, Pentti Somerharju, Jorma Virtanen, Juyang Huang, Kwan H. Cheng
Physics and Astronomy Faculty Research
Fluorescence and infrared spectroscopy and cholesterol oxidase activity were employed to investigate the effect of phosphatidylcholine (PC) acyl chain length mismatch on the lateral organizations of lipids in liquid-ordered dipalmitoyl-PC/dilauroyl-PC/cholesterol (DPPC/DLPC/CHOL) bilayers. Plots of steady-state fluorescence emission anisotropy of diphenylhexatriene (DPH) labeled PC (DPH-PC) embedded in the DPPC/DLPC/CHOL bilayers revealed significant peaks at several DPPC mole fractions (YDPPC) when the cholesterol mole fraction (XCHOL) was fixed to particular values. Analogously, the DPH-PC anisotropy peaked at several critical XCHOL’s when YDPPC was fixed. Acyl chain C−H and C═O vibrational peak frequencies of …
K Α₁ Radiation From Heavy, Heliumlike Ions Produced In Relativistic Collisions, Andrey S. Surzhykov, Ulrich D. Jentschura, Th H. Stohlker, Stephan Fritzsche
K Α₁ Radiation From Heavy, Heliumlike Ions Produced In Relativistic Collisions, Andrey S. Surzhykov, Ulrich D. Jentschura, Th H. Stohlker, Stephan Fritzsche
Physics Faculty Research & Creative Works
Bound-state transitions in few-electron, heavy ions following radiative electron capture are studied within the framework of the density matrix theory and the multiconfiguration Dirac-Fock approach. Special attention is paid to the K α1 (1 s1/2 2 p3/2 1.3PJ=1,2→1s21/2 1SJ=0) radiative decay of heliumlike uranium U90+ projectiles. This decay has recently been observed at the GSI facility in Darmstadt, giving rise to a surprisingly isotropic angular distribution, which is inconsistent with previous experiments and calculations based on a "one-particle" model. We show that the unexpected isotropy essentially results from …
Hysteresis Of Granular Fept:Ag Films With Perpendicular Anisotropy, M. L. Yan, Ralph Skomski, Arti Kashyap, L. Gao, Sy-Hwang Liou, David J. Sellmyer
Hysteresis Of Granular Fept:Ag Films With Perpendicular Anisotropy, M. L. Yan, Ralph Skomski, Arti Kashyap, L. Gao, Sy-Hwang Liou, David J. Sellmyer
Department of Physics and Astronomy: Faculty Publications
Intergranular interactions in nanostructured FePt:Ag thin films and their effect on magnetic hysteresis are investigated. The films, produced by multilayer deposition plus rapid thermal annealing, consist of FePt nanoparticles embedded in a silver matrix. They are investigated by magnetization measurements and magnetic force microscopy. Analytical model calculations, supported by micromagnetic simulations, are used to elucidate the relation between coercivity, hysteresis-loop slope, and spatial correlations during magnetization reversal. The analytical calculations yield simple expressions for the loop slope and the coercivity as a function of the intergranular exchange. Small intergranular exchange enhances the coercivity, but for strong exchange there is a …
Linearized Stability Analysis Of Accelerated Planar And Spherical Fluid Interfaces With Slow Compression, John D. Ramshaw, Peter A. Amendt
Linearized Stability Analysis Of Accelerated Planar And Spherical Fluid Interfaces With Slow Compression, John D. Ramshaw, Peter A. Amendt
Physics Faculty Publications and Presentations
We present linearized stability analyses of the effect of slow anisotropic compression or expansion on the growth of perturbations at accelerated fluid interfaces in both planar and spherical geometries. The interface separates two fluids with different densities, compressibilities, and compression rates. We show that a perturbation of large mode number on a spherical interface grows at precisely the same rate as a similar perturbation on a planar interface subjected to the same normal and transverse compression rates.
Electric Field Gradients In S-, P-, And D-Metal Diborides And The Effect Of Pressure On The Band Structure And TC In Mgb₂, Nadezhda I. Medvedeva, Alexander L. Ivanovskii, Julia E. Medvedeva, Arthur J. Freeman, Dmitrii L. Novikov
Electric Field Gradients In S-, P-, And D-Metal Diborides And The Effect Of Pressure On The Band Structure And TC In Mgb₂, Nadezhda I. Medvedeva, Alexander L. Ivanovskii, Julia E. Medvedeva, Arthur J. Freeman, Dmitrii L. Novikov
Physics Faculty Research & Creative Works
Results of full-potential linear muffin-tin orbital generalized gradient approximation calculations of the band structure and boron electric field gradients (EFG's) for the new medium-Tc superconductor MgB2 and related diborides MB2, M = Be, Al, Sc, Ti, V, Cr, Mo, and Ta are reported. The boron EFG variations are found to be related to specific features of their band structure and particularly to the M-B hybridization. The strong charge anisotropy at the B site in MgB2 is completely defined by the valence electrons - a property which sets MgB2 apart from other diborides. The boron …
Effect Of Rare Locally Ordered Regions On A Disordered Itinerant Quantum Antiferromagnet With Cubic Anisotropy, Rajesh S. Narayanan, Thomas Vojta
Effect Of Rare Locally Ordered Regions On A Disordered Itinerant Quantum Antiferromagnet With Cubic Anisotropy, Rajesh S. Narayanan, Thomas Vojta
Physics Faculty Research & Creative Works
We study the quantum phase transition of an itinerant antiferromagnet with cubic anisotropy in the presence of quenched disorder, paying particular attention to the locally ordered spatial regions that form in the Griffiths region. We derive an effective action where these rare regions are described in terms of static annealed disorder. A one-loop renormalization-group analysis of the effective action shows that for order-parameter dimensions p<4, the rare regions destroy the conventional critical behavior, and the renormalized disorder flows to infinity. For order-parameter dimensions p>4, the critical behavior is not influenced by the rare regions; it is described by the conventional dirty cubic fixed point. We also discuss the influence of the rare regions on the fluctuation-driven first-order transition …
Exchange Bias In Fef20-Copt Heterosystems With Perpendicular Anisotropy, Christian Binek
Exchange Bias In Fef20-Copt Heterosystems With Perpendicular Anisotropy, Christian Binek
Christian Binek Publications
The previous exchange bias effect is measured in heterosystems with perpendicular anisotropy consisting of Co/Pt multilayers on top of the (0 0 1) face of a previous FeF2 single crystal. The resulting previous exchange field HE exhibits a strong dependence on temperature and the axial freezing field, HF. Within the framework of an Ising-type model, the HE vs. T as well as the HE vs. HF data are explained in terms of the microscopic spin structure at the interface.
Freezing Field Dependance Of The Exchange Bias In Uniaxial Fef2-Copt Heterosystems With Perpendicular Anisotropy, Christian Binek
Freezing Field Dependance Of The Exchange Bias In Uniaxial Fef2-Copt Heterosystems With Perpendicular Anisotropy, Christian Binek
Christian Binek Publications
The exchange bias effect is measured for the first time in FeF2–CoPt heterosystems with perpendicular anisotropy. The exchange previous field exhibits a strong dependence on the axial previous freezing field. This behavior is explained in terms of the microscopic spin structure at the interface, which is established on cooling to below TN. We calculate the dependence of the spin structure on the previous freezing field within the framework of an Ising model. It takes into account the Zeeman energy as well as an antiferromagnetic exchange coupling between the adjacent layers at the interface.
Effect Of Slow Compression On The Linear Stability Of An Accelerated Shear Layer, John D. Ramshaw
Effect Of Slow Compression On The Linear Stability Of An Accelerated Shear Layer, John D. Ramshaw
Physics Faculty Publications and Presentations
An analysis is given of the effect of a slow uniform anisotropic compression or expansion on the linear stability of a normally accelerated planar interface between two fluids with different densities and tangential velocities, i.e., a combined Kelvin-Helmholtz and Rayleigh-Taylor instability, but generalized to an arbitrary time-dependent acceleration history. The compression is presumed to be sufficiently slow that the density remains uniform within each fluid and hence depends only on time. The perturbation is taken to be sinusoidal with amplitude h(t). The time evolution of h is determined by requiring pressure continuity across the interface in the usual way. The …
Magnetoelectric Néel Anisotropies, Ralph Skomski
Magnetoelectric Néel Anisotropies, Ralph Skomski
Ralph Skomski Publications
The applicability of Néel's pair model to metallic 3d surfaces and interfaces is explained in terms of the tight-binding moments theorem. The Néel model reproduces itinerant magnetism so long as the band structure is approximated by third-moment atomic-pair contributions. This establishes an atomic Néel description of interfaces and impurities. The Néel parameter g depends on the d-band filling and, to some extent, on the atomic structure.
Polarization Of Astronomical Maser Radiation, Moshe Elitzur
Polarization Of Astronomical Maser Radiation, Moshe Elitzur
Physics and Astronomy Faculty Publications
The polarization of maser radiation when the source is permeated by an aligned magnetic field is derived for arbitrary angular momenta of the transition states. This generalization is made possible by an analysis of the structure of the propagating waves in a frame aligned with the magnetic axis. The key elements in determining the polarization properties are the assumption of independent and incoherent pump and loss processes for all magnetic sublevels, and the beaming of maser radiation. The radiation propagating in the direction of maximal intensity growth is polarized according to the solutions derived by Goldreich, Keeley, and Kwan for …