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Full-Text Articles in Physics

From Critical Behavior To Catastrophic Runaways: Comparing Sheared Granular Materials With Bulk Metallic Glasses, Alan A. Long, Dmitry Denisov, Peter Schall, Todd C. Hufnagel, Xiaojun Gu, Wendelin J. Wright, Karin A. Dahmen Nov 2019

From Critical Behavior To Catastrophic Runaways: Comparing Sheared Granular Materials With Bulk Metallic Glasses, Alan A. Long, Dmitry Denisov, Peter Schall, Todd C. Hufnagel, Xiaojun Gu, Wendelin J. Wright, Karin A. Dahmen

Faculty Journal Articles

The flow of granular materials and metallic glasses is governed by strongly correlated, avalanche-like deformation. Recent comparisons focused on the scaling regimes of the small avalanches, where strong similarities were found in the two systems. Here, we investigate the regime of large avalanches by computing the temporal profile or “shape” of each one, i.e., the time derivative of the stress-time series during each avalanche. We then compare the experimental statistics and dynamics of these shapes in granular media and bulk metallic glasses. We complement the experiments with a mean-field model that predicts a critical size beyond which avalanches turn ...


Imaging Propagative Exciton Polaritons In Atomically Thin Wse2 Waveguides, F. Hu, Y. Luan, Jacob Speltz, D. Zhong, C. H. Liu, J. Yan, D. G. Mandrus, X. Xu, Zhe Fei Sep 2019

Imaging Propagative Exciton Polaritons In Atomically Thin Wse2 Waveguides, F. Hu, Y. Luan, Jacob Speltz, D. Zhong, C. H. Liu, J. Yan, D. G. Mandrus, X. Xu, Zhe Fei

Ames Laboratory Accepted Manuscripts

The exciton polariton (EP) is a half-light and half-matter quasiparticle that is promising for exploring both fundamental quantum phenomena as well as photonic applications. Van der Waals materials, such as transition-metal dichalcogenide (TMD), emerge as a promising nanophotonics platform due to its support of long propagative EPs even at room temperature. However, real-space studies have been limited to bulk crystal waveguides with a thickness no less than 60 nm. Here we report the nano-optical imaging of the transverse-electric EPs in WSe2 nanoflakes down to a few atomic layers, which can be turned on and off by tuning the polarization state ...


Predicting Complex Relaxation Processes In Metallic Glass, Yang Sun, Si-Xu Peng, Qun Yang, Feng Zhang, Meng-Hao Yang, Cai-Zhuang Wang, Kai-Ming Ho, Hai-Bin Yu Sep 2019

Predicting Complex Relaxation Processes In Metallic Glass, Yang Sun, Si-Xu Peng, Qun Yang, Feng Zhang, Meng-Hao Yang, Cai-Zhuang Wang, Kai-Ming Ho, Hai-Bin Yu

Ames Laboratory Accepted Manuscripts

Relaxation processes significantly influence the properties of glass materials. However, understanding their specific origins is difficult; even more challenging is to forecast them theoretically. In this study, using microseconds molecular dynamics simulations together with an accurate many-body interaction potential, we predict that an Al90Sm10 metallic glass would have complex relaxation behaviors: In addition to the main (α) relaxation, the glass (i) shows a pronounced secondary (β) relaxation at cryogenic temperatures and (ii) exhibits an anomalous relaxation process (α2) accompanying α relaxation. Both of the predictions are verified by experiments. Computational simulations reveal the microscopic origins of relaxation processes: while the ...


Force Oscillations Distort Avalanche Shapes, Louis W. Mcfaul, Wendelin J. Wright, Jordan Sickle, Karin A. Dahmen Sep 2019

Force Oscillations Distort Avalanche Shapes, Louis W. Mcfaul, Wendelin J. Wright, Jordan Sickle, Karin A. Dahmen

Faculty Journal Articles

Contradictory scaling behavior in experiments testing the principle of universality may be due to external oscillations. Thus, the effect of damped oscillatory external forces on slip avalanches in slowly deformed solids is simulated using a mean-field model. Akin to a resonance effect, oscillatory driving forces change the dynamics of avalanches with durations close to the oscillation period. This problem can be avoided by tuning mechanical resonance frequencies away from the range of the inverse avalanche durations. The results provide critical guidance for experimental tests for universality and a quantitative understanding of avalanche dynamics under a wide range of driving conditions.


Analysis Of The London Penetration Depth In Ni-Doped Cakfe4 As4, D. Torsello, Kyuil Cho, Kamal R. Joshi, Sunil Ghimire, G. A. Ummarino, Naufer Nusran, Makariy A. Tanatar, William R. Meier, Mingyu Xu, Sergey L. Bud’Ko, Paul C. Canfield, G. Ghigo, Ruslan Prozorov Sep 2019

Analysis Of The London Penetration Depth In Ni-Doped Cakfe4 As4, D. Torsello, Kyuil Cho, Kamal R. Joshi, Sunil Ghimire, G. A. Ummarino, Naufer Nusran, Makariy A. Tanatar, William R. Meier, Mingyu Xu, Sergey L. Bud’Ko, Paul C. Canfield, G. Ghigo, Ruslan Prozorov

Ames Laboratory Accepted Manuscripts

We report combined experimental and theoretical analysis of superconductivity in CaK(Fe1−xNix)4As4 (CaK1144) for x=0, 0.017, and 0.034. To obtain the superfluid density ρ=[1+ΔλL(T)/λL(0)]−2, the temperature dependence of the London penetration depth ΔλL(T) was measured by using a tunnel-diode resonator (TDR) and the results agreed with the microwave coplanar resonator (MWR) with the small differences accounted for by considering a three orders of magnitude higher frequency of MWR. The absolute value of λL(T≪Tc)≈λL(0) was measured by using MWR, λL(5K)≈170±20 nm, which ...


Slowing Down Of Spin Glass Correlation Length Growth: Simulations Meet Experiments, Qiang Zhai, V. Martin-Mayor, Deborah L. Schlagel, Gregory G. Kenning, Raymond L. Orbach Sep 2019

Slowing Down Of Spin Glass Correlation Length Growth: Simulations Meet Experiments, Qiang Zhai, V. Martin-Mayor, Deborah L. Schlagel, Gregory G. Kenning, Raymond L. Orbach

Ames Laboratory Accepted Manuscripts

The growth of the spin glass correlation length has been measured as a function of the waiting time tw on a single crystal of CuMn (6 at. %), reaching values ξ∼150 nm, larger than any other glassy correlation length measured to date. We find an aging rate dlntw/dlnξ larger than found in previous measurements, which evinces a dynamic slowing down as ξ grows. Our measured aging rate is compared with simulation results by the Janus Collaboration. After critical effects are taken into account, we find excellent agreement with the Janus data.


Multiple Ferromagnetic Transitions And Structural Distortion In The Van Der Waals Ferromagnet Vi3 At Ambient And Finite Pressures, Elena Gati, Yuji Inagaki, Tai Kong, Robert J. Cava, Yuji Furukawa, Paul C. Canfield, Sergey L. Bud’Ko Sep 2019

Multiple Ferromagnetic Transitions And Structural Distortion In The Van Der Waals Ferromagnet Vi3 At Ambient And Finite Pressures, Elena Gati, Yuji Inagaki, Tai Kong, Robert J. Cava, Yuji Furukawa, Paul C. Canfield, Sergey L. Bud’Ko

Ames Laboratory Accepted Manuscripts

We present a combined study of zero-field (51) V and I-127 NMR at ambient pressure and specific heat and magnetization measurements under pressure up to 2.08 GPa on bulk single crystals of the van der Waals ferromagnet VI3. At ambient pressure, our results consistently demonstrate that VI3 undergoes a structural transition at T-s approximate to 78 K, followed by two subsequent ferromagnetic transitions at T-FM1 approximate to 50 K and T-FM2 approximate to 36 K upon cooling. At lowest temperature (T < T-FM2), two magnetically ordered V sites exist, whereas only one magnetically ordered V site is observed for T-FM1 < T < T-FM2. Whereas T-FM1 is almost unaffected by external pressure, T-FM2 is highly responsive to pressure and merges with the T-FM1 line at p 0.6 GPa. At even higher pressures (p approximate to 1.25 GPa), the T-FM2 line merges with the structural transition at T-s which becomes moderately suppressed with p for p < 1.25 GPa. Taken together, our data point toward a complex magnetic structure and an interesting interplay of magnetic and structural degrees of freedom in VI3.


Evolution Of Structural, Magnetic, And Transport Properties In Mnbi2−X Sbx Te4, Jiaqiang Yan, Satoshi Okamoto, Michael A. Mcguire, Andrew F. May, Robert J. Mcqueeney, Brian C. Sales Sep 2019

Evolution Of Structural, Magnetic, And Transport Properties In Mnbi2−X Sbx Te4, Jiaqiang Yan, Satoshi Okamoto, Michael A. Mcguire, Andrew F. May, Robert J. Mcqueeney, Brian C. Sales

Ames Laboratory Accepted Manuscripts

Here we report the evolution of structural, magnetic, and transport properties in MnBi2−xSbxTe4(0≤x≤2) single crystals. MnSb2Te4, isostructural to MnBi2Te4, is successfully synthesized in single-crystal form. Magnetic measurements suggest an antiferromagnetic order below TN=19K for MnSb2Te4 with the magnetic moments aligned along the crystallographic c axis. With increasing Sb content in MnBi2−xSbxTe4, the a-lattice parameter decreases linearly following Vegard's law, while the c-lattice parameter shows little compositional dependence. The contraction along a is caused by the reduction of the Mn-Te-Mn bond angle, while the Mn-Te bond length remains nearly constant. The antiferromagnetic ordering temperature ...


Correlations Between Short- And Long-Time Relaxation In Colloidal Supercooled Liquids And Glasses, Chandan K. Mishra, Xiaoguang Ma, Piotr Habdas, Kevin B. Aptowicz, A. G. Yodh Aug 2019

Correlations Between Short- And Long-Time Relaxation In Colloidal Supercooled Liquids And Glasses, Chandan K. Mishra, Xiaoguang Ma, Piotr Habdas, Kevin B. Aptowicz, A. G. Yodh

Physics

Spatiotemporal dynamics of short- and long-time structural relaxation are measured experimentally as a function of packing fraction, φ, in quasi-two-dimensional colloidal supercooled liquids and glasses. The relaxation times associated with long-time dynamic heterogeneity and short-time intracage motion are found to be strongly correlated and to grow by orders of magnitude with increasing φ toward dynamic arrest. We find that clusters of fast particles on the two timescales often overlap, and, interestingly, the distribution of minimum-spatial-separation between closest nonoverlapping clusters across the two timescales is revealed to be exponential with a decay length that increases with φ. In total, the experimental ...


Tunneling Anisotropic Magnetoresistance In Ferroelectric Tunnel Junctions, Artem Alexandrov, M. Ye. Zhuravlev, Evgeny Y. Tsymbal Aug 2019

Tunneling Anisotropic Magnetoresistance In Ferroelectric Tunnel Junctions, Artem Alexandrov, M. Ye. Zhuravlev, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Using a simple quantum-mechanical model, we explore a tunneling anisotropic magnetoresistance (TAMR) effect in ferroelectric tunnel junctions (FTJs) with a ferromagnetic electrode and a ferroelectric barrier layer, where spontaneous polarization gives rise to the Rashba and Dresselhaus spin-orbit coupling (SOC). For realistic parameters of the model, we predict sizable TAMR measurable experimentally. For asymmetric FTJs, whose electrodes have different work functions, the built-in electric field affects the SOC parameters and leads to TAMR being dependent on the ferroelectric polarization direction. The SOC change with polarization switching affects tunneling conductance, revealing an alternative mechanism of tunneling electroresistance. These results demonstrate alternative ...


Fatigue-Resistant High-Performance Elastocaloric Materials Via Additive Manufacturing, Huilong Hou, Emrah Simsek, Tao Ma, Nathan S. Johnson, Suxin Qian, Cheikh Cissé, Drew Stasak, Naila Al Hasan, Lin Zhou, Yunho Hwang, Reinhard Radermacher, Valery I. Levitas, Matthew J. Kramer, Mohsen Asle Zaeem, Aaron P. Stebner, Ryan T. Ott, Jun Cui, Ichiro Takeuchi Aug 2019

Fatigue-Resistant High-Performance Elastocaloric Materials Via Additive Manufacturing, Huilong Hou, Emrah Simsek, Tao Ma, Nathan S. Johnson, Suxin Qian, Cheikh Cissé, Drew Stasak, Naila Al Hasan, Lin Zhou, Yunho Hwang, Reinhard Radermacher, Valery I. Levitas, Matthew J. Kramer, Mohsen Asle Zaeem, Aaron P. Stebner, Ryan T. Ott, Jun Cui, Ichiro Takeuchi

Aerospace Engineering Publications

Elastocaloric cooling, which exploits the latent heat released and absorbed as stress-induced phase transformations are reversibly cycled in shape memory alloys, has recently emerged as a frontrunner in non-vapor-compression cooling technologies. The intrinsically high thermodynamic efficiency of elastocaloric materials is limited only by work hysteresis. Here, we report on creating high-performance low-hysteresis elastocaloric cooling materials via additive manufacturing of Titanium-Nickel (Ti-Ni) alloys. Contrary to established knowledge of the physical metallurgy of Ti-Ni alloys, intermetallic phases are found to be beneficial to elastocaloric performances when they are combined with the binary Ti-Ni compound in nanocomposite configurations. The resulting microstructure gives rise ...


Magnetoelectric Effect At The Ni/Hfo2 Interface Induced By Ferroelectric Polarization, Qiong Yang, Lingling Tao, Zhen Jiang, Yichun Zhou, Evgeny Tsymbal, Vitaly Alexandrov Aug 2019

Magnetoelectric Effect At The Ni/Hfo2 Interface Induced By Ferroelectric Polarization, Qiong Yang, Lingling Tao, Zhen Jiang, Yichun Zhou, Evgeny Tsymbal, Vitaly Alexandrov

Evgeny Tsymbal Publications

Driven by the technological importance of the recently discovered ferroelectric HfO2, we explore a magnetoelectric effect at the HfO2-based ferroelectric-ferromagnetic interface. Using density-functionaltheory calculations of the Ni/HfO2/Ni (001) heterostructure as a model system, we predict a stable and sizable ferroelectric polarization in a few-nm-thick HfO2 layer. For the Ni/HfO2 interface with opposite polarization directions (pointing to or away from the interface), we find a sizable difference in the interfacial Ni—O bonding, resulting in dissimilar degrees of depletion of the electron density around the interface. The latter affects the relative population ...


Self-Consistent Two-Gap Description Of Mgb2 Superconductor, Hyunsoo Kim, Kyuil Cho, Makariy A. Tanatar, Valentin Taufour, Stella K. Kim, Sergey L. Bud’Ko, Paul C. Canfield, Vladimir G. Kogan, Ruslan Prozorov Aug 2019

Self-Consistent Two-Gap Description Of Mgb2 Superconductor, Hyunsoo Kim, Kyuil Cho, Makariy A. Tanatar, Valentin Taufour, Stella K. Kim, Sergey L. Bud’Ko, Paul C. Canfield, Vladimir G. Kogan, Ruslan Prozorov

Ames Laboratory Accepted Manuscripts

A self-consistent two-gap γ -model is used to quantitatively describe several thermodynamic properties of MgB 2 superconductor. The superconducting coupling matrix, νij , was obtained from the fitting of the superfluid density in the entire superconducting temperature range. Using this input, temperature-dependent superconducting gaps, specific heat, and upper critical fields were calculated with no adjustable parameters and compared with the experimental data as well as with the first-principles calculations. The observed agreement between fit and data shows that γ -model provides adequate quantitative description of the two-gap superconductivity in MgB 2 and may serve as a relatively simple and versatile self-consistent ...


Computational Studies Of Thermal Properties And Desalination Performance Of Low-Dimensional Materials, Yang Hong Aug 2019

Computational Studies Of Thermal Properties And Desalination Performance Of Low-Dimensional Materials, Yang Hong

Student Research Projects, Dissertations, and Theses - Chemistry Department

During the last 30 years, microelectronic devices have been continuously designed and developed with smaller size and yet more functionalities. Today, hundreds of millions of transistors and complementary metal-oxide-semiconductor cells can be designed and integrated on a single microchip through 3D packaging and chip stacking technology. A large amount of heat will be generated in a limited space during the operation of microchips. Moreover, there is a high possibility of hot spots due to non-uniform integrated circuit design patterns as some core parts of a microchip work harder than other memory parts. This issue becomes acute as stacked microchips get ...


Suppression Of Ferromagnetic Spin Fluctuations In The Filled Skutterudite Superconductor Sros4 As12 Revealed By 75as Nmr-Nqr Measurements, Qing-Ping Ding, K. Nishine, Y. Kawamura, J. Hayashi, C. Sekine, Yuji Furukawa Aug 2019

Suppression Of Ferromagnetic Spin Fluctuations In The Filled Skutterudite Superconductor Sros4 As12 Revealed By 75as Nmr-Nqr Measurements, Qing-Ping Ding, K. Nishine, Y. Kawamura, J. Hayashi, C. Sekine, Yuji Furukawa

Ames Laboratory Accepted Manuscripts

Motivated by the recent observation of ferromagnetic spin correlations in the filled skutterudite SrFe4As12 [Q.-P. Ding et al., Phys. Rev. B 98, 155149 (2018)], we have carried out As-75 nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements to investigate the role of magnetic fluctuations in the newly discovered isostructural superconductor SrOs4As12 with a superconducting transition temperature of T-c similar to 4.8 K. Knight shift K determined by the NQR spectrum under a small magnetic field (<= 0.5 T) is nearly independent of temperature, consistent with the temperature dependence of the magnetic susceptibility. The nuclear spin-lattice relaxation rate divided by temperature, 1/T1T, is nearly independent of temperature above similar to 50 K and increases slightly with decreasing temperature below the temperature. The temperature dependence is reasonably explained by a simple model where a flat band structure with a small ledge near the Fermi energy is assumed. By comparing the present NMR data with those in SrFe4As12, we found that the values of vertical bar K vertical bar and 1/T1T in SrOs4As12 are smaller than those in SrFe4As12, indicating no obvious ferromagnetic spin correlations in SrOs4As12. From the temperature dependence of 1/T-1 in the superconducting state, an s-wave superconductivity is realized.


Role Of The Fermi Surface For The Pressure-Tuned Nematic Transition In The Bafe2 As2 Family, Elena Gati, Li Xiang, Sergey L. Bud’Ko, Paul C. Canfield Aug 2019

Role Of The Fermi Surface For The Pressure-Tuned Nematic Transition In The Bafe2 As2 Family, Elena Gati, Li Xiang, Sergey L. Bud’Ko, Paul C. Canfield

Ames Laboratory Accepted Manuscripts

The tetragonal-to-orthorhombic phase transition at Ts, which precedes the antiferromagnetic phase transition at TN in many iron-based superconductors, is considered one of the manifestations of electronic nematic order. By constructing temperature-pressure phase diagrams of pure and Co-doped BaFe2As2, we study the relation of Ts and TN under pressure p. Our data disclose two qualitatively different regimes in which ΔT=Ts−TN either increases or decreases with p. We provide experimental evidence that the transition between the two regimes may be associated with sudden changes of the Fermi surface topology. Therefore, our results not only support the electronic origin of the ...


Skyrmions And Spirals In Mnsi Under Hydrostatic Pressure, L. J. Bannenberg, R. Sadykov, R. M. Dalgliesh, C. Goodway, Deborah L. Schlagel, Thomas A. Lograsso, P. Falus, E. Lelièvre-Berna, A. O. Leonov, C. Pappas Aug 2019

Skyrmions And Spirals In Mnsi Under Hydrostatic Pressure, L. J. Bannenberg, R. Sadykov, R. M. Dalgliesh, C. Goodway, Deborah L. Schlagel, Thomas A. Lograsso, P. Falus, E. Lelièvre-Berna, A. O. Leonov, C. Pappas

Ames Laboratory Accepted Manuscripts

The archetype cubic chiral magnet MnSi is home to some of the most fascinating states in condensed matter, such as skyrmions and a non-Fermi-liquid behavior in conjunction with a topological Hall effect under hydrostatic pressure. Using small angle neutron scattering, we study the evolution of the helimagnetic, conical, and skyrmionic correlations with increasing hydrostatic pressure. We show that the helical propagation vector smoothly reorients from ⟨111⟩ to ⟨100⟩ at intermediate pressures. At higher pressures, above the critical pressure, the long-range helimagnetic order disappears at zero magnetic field. Nevertheless, skyrmion lattices and conical spirals form under magnetic fields, in a part ...


Effect Of Ni Doping On Vortex Pinning In Cak (Fe1−X Nix)4as4 Single Crystals, N. Haberkorn, Mingyu Xu, William R. Meier, J. Schmidt, Sergey L. Bud’Ko, Paul C. Canfield Aug 2019

Effect Of Ni Doping On Vortex Pinning In Cak (Fe1−X Nix)4as4 Single Crystals, N. Haberkorn, Mingyu Xu, William R. Meier, J. Schmidt, Sergey L. Bud’Ko, Paul C. Canfield

Ames Laboratory Accepted Manuscripts

We study the correlation between chemical composition and vortex dynamics in Ni-doped CaK(Fe1−xNix)4As4 (x=0, 0.015, 0.025, 0.03, and 0.05) single crystals by performing measurements of the critical current densities Jc and the flux creep rates S. The magnetic relaxation of all the crystals is well described by the collective creep theory. The samples display a glassy exponent μ within the predictions for vortex bundles in a weak pinning scenario and relatively small characteristic pinning energy (U0<100K). The undoped crystals display modest Jc values at low temperatures and high magnetic fields applied along the c axis. Jc(T) dependences at high fields display an unusual peak. The enhancement in Jc(T) matches with an increase in U0 and the appearance of a second peak in the magnetization. As Ni doping increases, whereas there is a monotonic decrease in Tc there is a nonmonotonic change in Jc. Initially Jc increases, reaching a maximum value for x=0.015, and then Jc decreases for x≥0.025. This change in Jc(x) is coincident with the onset of antiferromagnetic order. The magnetic field dependence of Jc(H) also manifests a change in behavior between these x values. The analysis of the vortex dynamics for small and intermediate magnetic fields shows a gradual evolution in the glassy exponent μ with Ni content, x. This implies that there is no appreciable change in the mechanism that determines the vortex relaxation.


Impact Of Damping On The Superconducting Gap Dynamics Induced By Intense Terahertz Pulses, Tianbai Cui, Xu Yang, Chirag Vaswani, Jigang Wang, Rafael M. Fernandes, Peter P. Orth Aug 2019

Impact Of Damping On The Superconducting Gap Dynamics Induced By Intense Terahertz Pulses, Tianbai Cui, Xu Yang, Chirag Vaswani, Jigang Wang, Rafael M. Fernandes, Peter P. Orth

Ames Laboratory Accepted Manuscripts

We investigate the interplay between coherent gap dynamics and damping in superconductors taken out of equilibrium by strong optical pulses with subgap terahertz frequencies. A semiphenomenological formalism is developed to include the damping within the electronic subsystem that arises from effects beyond Bardeen-Cooper-Schrieffer mean-field theory, such as interactions between Bogoliubov quasiparticles and decay of the Higgs mode. These processes, conveniently expressed as longitudinal T1 and transverse T2 relaxation times in the standard pseudospin language for superconductors, cause the gap amplitude to be suppressed after the pulse is turned off, but before the timescale where thermalization occurs due to coupling to ...


Competing Magnetic Phases And Itinerant Magnetic Frustration In Srco2 As2, Bing Li, Benjamin G. Ueland, W. T. Jayasekara, D. L. Abernathy, N. S. Sangeetha, David C. Johnston, Qing-Ping Ding, Yuji Furukawa, Peter P. Orth, Andreas Kreyssig, Alan I. Goldman, Robert J. Mcqueeney Aug 2019

Competing Magnetic Phases And Itinerant Magnetic Frustration In Srco2 As2, Bing Li, Benjamin G. Ueland, W. T. Jayasekara, D. L. Abernathy, N. S. Sangeetha, David C. Johnston, Qing-Ping Ding, Yuji Furukawa, Peter P. Orth, Andreas Kreyssig, Alan I. Goldman, Robert J. Mcqueeney

Ames Laboratory Accepted Manuscripts

Whereas magnetic frustration is typically associated with local-moment magnets in special geometric arrangements, here we show that SrCo2As2 is a candidate for frustrated itinerant magnetism. Using inelastic neutron scattering (INS), we find that antiferromagnetic (AF) spin fluctuations develop in the square Co layers of SrCo2As2 below T approximate to 100 K centered at the stripe-type AF propagation vector of (1/2, 1/2), and that their development is concomitant with a suppression of the uniform magnetic susceptibility determined via magnetization measurements. We interpret this switch in spectral weight as signaling a temperature-induced crossover from an instability toward ferromagnetism ordering to ...


Distinct Pressure Evolution Of Coupled Nematic And Magnetic Orders In Fese, Anna E. Böhmer, Karunakar Kothapalli, Wageesha T. Jayasekara, John M. Wilde, Bing Li, Aashish Sapkota, Benjamin G. Ueland, Pinaki Das, Yumin Xiao, Wenli Bi, Jiyong Zhao, E. Ercan Alp, Sergey L. Bud’Ko, Paul C. Canfield, Alan I. Goldman, Andreas Kreyssig Aug 2019

Distinct Pressure Evolution Of Coupled Nematic And Magnetic Orders In Fese, Anna E. Böhmer, Karunakar Kothapalli, Wageesha T. Jayasekara, John M. Wilde, Bing Li, Aashish Sapkota, Benjamin G. Ueland, Pinaki Das, Yumin Xiao, Wenli Bi, Jiyong Zhao, E. Ercan Alp, Sergey L. Bud’Ko, Paul C. Canfield, Alan I. Goldman, Andreas Kreyssig

Ames Laboratory Accepted Manuscripts

We present a microscopic study of nematicity and magnetism in FeSe over a wide temperature and pressure range using high-energy x-ray diffraction and time-domain Mössbauer spectroscopy. The low-temperature magnetic hyperfine field increases monotonically up to ∼ 6 GPa. The orthorhombic distortion initially decreases under increasing pressure but is stabilized at intermediate pressures by cooperative coupling to the pressure-induced magnetic order. Close to the reported maximum of the superconducting critical temperature at p = 6.8 GPa , the orthorhombic distortion suddenly disappears and a new tetragonal magnetic phase occurs. The pressure and temperature evolution of the structural and magnetic order parameters suggests that ...


Hole Doping And Antiferromagnetic Correlations Above The Néel Temperature Of The Topological Semimetal (Sr1-X Kx) Mnsb2, Yong Liu, Farhan Islam, Kevin W. Dennis, Wei Tian, Benjamin G. Ueland, Robert J. Mcqueeney, David Vaknin Jul 2019

Hole Doping And Antiferromagnetic Correlations Above The Néel Temperature Of The Topological Semimetal (Sr1-X Kx) Mnsb2, Yong Liu, Farhan Islam, Kevin W. Dennis, Wei Tian, Benjamin G. Ueland, Robert J. Mcqueeney, David Vaknin

Ames Laboratory Accepted Manuscripts

Neutron diffraction and magnetic susceptibility studies of orthorhombic single crystal (Sr0.97K0.03)MnSb2 confirm the three-dimensional (3D) C-type antiferromagnetic (AFM) ordering of the Mn2+ moments at TN=305±3 K, which is slightly higher than that of the parent SrMnSb2 with TN=297±3 K. Susceptibility measurements of the K-doped and parent crystals above TN are characteristic of 2D AFM systems. This is consistent with high-temperature neutron diffraction of the parent compound that displays persisting 2D AFM correlations well above TN to at least ∼560 K with no evidence of a ferromagnetic phase. Analysis of the de Haas–van ...


Temperature-Dependent Anisotropies Of Upper Critical Field And London Penetration Depth, V. G. Kogan, Ruslan Prozorov, A. E. Koshelev Jul 2019

Temperature-Dependent Anisotropies Of Upper Critical Field And London Penetration Depth, V. G. Kogan, Ruslan Prozorov, A. E. Koshelev

Ames Laboratory Accepted Manuscripts

We show on a few examples of one-band materials with spheroidal Fermi surfaces and anisotropic order parameters that anisotropies γH of the upper critical field and γλ of the London penetration depth depend on temperature, a feature commonly attributed to multiband superconductors. The parameters γH and γλ may have opposite temperature dependences or may change in the same direction depending on the Fermi-surface shape and on the character of the gap nodes. For two-band systems, the behavior of anisotropies is affected by the ratios of bands densities of states, Fermi velocities, anisotropies, and order parameters. We investigate in detail the ...


Anisotropy And Orbital Moment In Sm-Co Permanent Magnets, Bhaskar Das, Renu Choudhary, Ralph Skomski, Balamurugan Balasubramanian, Arjun K. Pathak, Durga Paudyal, David J. Sellmyer Jul 2019

Anisotropy And Orbital Moment In Sm-Co Permanent Magnets, Bhaskar Das, Renu Choudhary, Ralph Skomski, Balamurugan Balasubramanian, Arjun K. Pathak, Durga Paudyal, David J. Sellmyer

Ames Laboratory Accepted Manuscripts

Structural and magnetic properties of iron-free and iron-substituted SmCo5 have been investigated theoretically and experimentally. The nanocrystalline ribbons of SmCo5−xFex(0≤x≤2), which were produced by rapid solidification, crystallize in the hexagonal CaCu5 structure for x≤0.75. Small Fe additions (x=0.25) substantially improve the coercivity, from 0.45 to 2.70 T, which we interpret as combined intrinsic and extrinsic effect. Most of our findings are consistent with past samarium-cobalt research, but some are at odds with findings that have seemingly been well established through decades of rare-earth transition-metal research. In particular, our local spin-density ...


Antiferromagnetic Stacking Of Ferromagnetic Layers And Doping-Controlled Phase Competition In Ca1−X Srx Co2−Y As2, Bing Li, Yuriy Sizyuk, Nediadath S. Sangeetha, John M. Wilde, Pinaki Das, W. Tian, David C. Johnston, Alan I. Goldman, Andreas Kreyssig, Peter P. Orth, Robert J. Mcqueeney, Benjamin G. Ueland Jul 2019

Antiferromagnetic Stacking Of Ferromagnetic Layers And Doping-Controlled Phase Competition In Ca1−X Srx Co2−Y As2, Bing Li, Yuriy Sizyuk, Nediadath S. Sangeetha, John M. Wilde, Pinaki Das, W. Tian, David C. Johnston, Alan I. Goldman, Andreas Kreyssig, Peter P. Orth, Robert J. Mcqueeney, Benjamin G. Ueland

Ames Laboratory Accepted Manuscripts

In search of a quantum phase transition between the two-dimensional (2D) ferromagnetism of CaCo2−yAs2 and stripe-type antiferromagnetism in SrCo2 As2, we instead find evidence for 1D magnetic frustration between magnetic square Co layers. We present neutron-diffraction data for Ca1−x Srx Co2−y As2 that reveal a sequence of x -dependent magnetic transitions which involve different stacking of 2 D ferromagnetically aligned layers with different magnetic anisotropy. We explain the x-dependent changes to the magnetic order by utilizing classical analytical calculations of a 1D Heisenberg model where single-ion magnetic anisotropy and frustration of antiferromagnetic nearest- and next-nearest-layer exchange interactions ...


Tuning Phase-Stability And Short-Range Order Through Ai-Doping In (Cocrfemn)100-Xaix High Entropy Alloys, Prashant Singh, Amalraj Marshal, A. V. Smirnov, Aayush Sharma, Ganesh Balasubramanian, K. G. Pradeep, Duane D. Johnson Jul 2019

Tuning Phase-Stability And Short-Range Order Through Ai-Doping In (Cocrfemn)100-Xaix High Entropy Alloys, Prashant Singh, Amalraj Marshal, A. V. Smirnov, Aayush Sharma, Ganesh Balasubramanian, K. G. Pradeep, Duane D. Johnson

Ames Laboratory Accepted Manuscripts

For (CoCrFeMn)100−xAlx high-entropy alloys, we investigate the phase evolution with increasing Al content (0≤x≤20 at.%). From first-principles theory, aluminum doping drives the alloy structurally from fcc to bcc separated by a narrow two-phase region (fcc+bcc), which is well supported by our experiments. Using KKR-CPA electronic-structure calculations, we highlight the effect of Al doping on the formation enthalpy (alloy stability) and electronic dispersion of (CoCrFeMn)100−xAlx alloys. As chemical short-range order indicates the nascent local order, and entropy changes, as well as expected low-temperature ordering behavior, we use KKR-CPA-based thermodynamic linear response to predict the ...


A Room-Temperature Ferroelectric Semimetal, Pankaj Sharma, Fei-Xiang Xiang, Ding-Fu Shao, Dawei Zhang, Evgeny Y. Tsymbal, Alex R. Hamilton, Jan Seidel Jul 2019

A Room-Temperature Ferroelectric Semimetal, Pankaj Sharma, Fei-Xiang Xiang, Ding-Fu Shao, Dawei Zhang, Evgeny Y. Tsymbal, Alex R. Hamilton, Jan Seidel

Evgeny Tsymbal Publications

Coexistence of reversible polar distortions and metallicity leading to a ferroelectric metal, first suggested by Anderson and Blount in 1965, has so far remained elusive. Electrically switchable intrinsic electric polarization, together with the direct observation of ferroelectric domains, has not yet been realized in a bulk crystalline metal, although incomplete screening by mobile conduction charges should, in principle, be possible. Here, we provide evidence that native metallicity and ferroelectricity coexist in bulk crystalline van der Waals WTe2 by means of electrical transport, nanoscale piezoresponse measurements, and first-principles calculations. We show that, despite being a Weyl semimetal, WTe2 has switchable spontaneous ...


Single Pair Of Weyl Fermions In The Half-Metallic Semimetal Eucd2as2, Lin-Lin Wang, Na Hyun Jo, Brinda Kuthanazhi, Yun Wu, Robert J. Mcqueeney, Adam Kaminski, Paul C. Canfield Jun 2019

Single Pair Of Weyl Fermions In The Half-Metallic Semimetal Eucd2as2, Lin-Lin Wang, Na Hyun Jo, Brinda Kuthanazhi, Yun Wu, Robert J. Mcqueeney, Adam Kaminski, Paul C. Canfield

Ames Laboratory Accepted Manuscripts

Materials with the ideal case of a single pair of Weyl points (WPs) are highly desirable for elucidating the unique properties of Weyl fermions. EuC d 2 A s 2 is an antiferromagnetic topological insulator or Dirac semimetal depending on the different magnetic configurations. Using first-principles band-structure calculations, we show that inducing ferromagnetism in EuC d 2 A s 2 can generate a single pair of WPs from splitting the single pair of antiferromagnetic Dirac points due to its half-metallic nature. Analysis with a low-energy effective Hamiltonian shows that a single pair of WPs is obtained in EuC d 2 ...


Magnetic Structure And Magnetization Of Z -Axis Helical Heisenberg Antiferromagnets With Xy Anisotropy In High Magnetic Fields Transverse To The Helix Axis At Zero Temperature, David C. Johnston Jun 2019

Magnetic Structure And Magnetization Of Z -Axis Helical Heisenberg Antiferromagnets With Xy Anisotropy In High Magnetic Fields Transverse To The Helix Axis At Zero Temperature, David C. Johnston

Ames Laboratory Accepted Manuscripts

A helix has a wave vector along the z axis with the magnetic moments ferromagnetically aligned within xy planes with a turn angle kd between the moments in adjacent planes in transverse field H=Hxˆi=0. The magnetic structure and x-axis average magnetization per spin of this system in a classical XY anisotropy field HA is studied versus kd, HA, and large Hx at zero temperature. For values of HA below a kd-dependent maximum value, the xy helix phase transitions with increasing Hx into a spin-flop (SF) phase where the ordered moments have x, y, and z components. The moments ...


Two-Dimensional Ordering And Collective Magnetic Excitations In The Dilute Ferromagnetic Topological Insulator (Bi0.95 Mn0.05)2 Te3, David Vaknin, Daniel M. Pajerowski, Deborah L. Schlagel, Kevin W. Dennis, Robert Mcqueeney Jun 2019

Two-Dimensional Ordering And Collective Magnetic Excitations In The Dilute Ferromagnetic Topological Insulator (Bi0.95 Mn0.05)2 Te3, David Vaknin, Daniel M. Pajerowski, Deborah L. Schlagel, Kevin W. Dennis, Robert Mcqueeney

Ames Laboratory Accepted Manuscripts

Employing elastic and inelastic neutron scattering (INS) techniques, we report on the microscopic properties of the ferromagnetism in the dilute magnetic topological insulator (Bi0.95Mn0.05)2 Te3. Neutron diffraction of polycrystalline samples shows the ferromagnetic (FM) ordering is long range within the basal plane, and mainly two dimensional (2D) in character with short-range correlations between layers below T C ≈ 13 K. Remarkably, we observe gapped and collective magnetic excitations in this dilute magnetic system. The excitations appear typical of quasi-2D FM systems despite the severe broadening of short-wavelength magnons which is expected from the random spatial distribution of Mn ...