Intermediate Plateau Research Articles

Imaging Magnetization Switching Induced by Spin-Orbit Torque in Perpendicularly Magnetized Ta/CoFeB Structure

We report the study of current-induced magnetization switching in the Ta/CoFeB heterostructures by simultaneous magneto-electrical transport and magneto-optical Kerr effect (MOKE) microscopy measurements. Although the anomalous Hall hysteresis loop summarizes the general switching behaviors, the supplementary MOKE data can provide spatial and temporal information to visualize the magnetic domain evolution as functions of the applied current and the in-plane magnetic field. More importantly, when the initial magnetic field is not sufficient enough, the interfacial Dzyaloshinskii–Moriya interaction (DMI) would modulate the spin-orbit torque (SOT) current switching dynamics and lead to the formation of the intermediate Hall resistance plateau with meta-stable tilted domain texture. Our work elucidates the importance of the applied in-plane field and unveils an effective approach to investigate the SOT/DMI-related phenomena in symmetry-breaking magnetic heterostructures.

Magnetization plateaus and bipartite entanglement of an exactly solved spin-1/2 Ising-Heisenberg orthogonal-dimer chain

Spin-1/2 orthogonal-dimer chain composed of regularly alternating Ising and Heisenberg dimers is exactly solved in a presence of the magnetic field by the transfer-matrix method. It is shown that the ground-state phase diagram involves in total six different phases. Besides the ferromagnetic phase with fully polarized spins one encounters the singlet antiferromagnetic and modulated antiferromagnetic phases manifested in zero-temperature magnetization curves as zero magnetization plateau, the frustrated ferrimagnetic and singlet ferrimagnetic phases causing existence of an intermediate one-half magnetization plateau, and finally, the intriguing modulated ferrimagnetic phase with a translationally broken symmetry leading to an unconventional one-quarter magnetization plateau. The quantum character of individual ground states is quantified via the concurrence, which measures a strength of the bipartite entanglement within the pure and mixed states of the Heisenberg dimers at zero as well as nonzero temperatures. The parameter region, where the bipartite entanglement may be in contrast to general expectations reinforced upon increasing of temperature and/or magnetic field, is elucidated.

Breakdown of intermediate one-half magnetization plateau of spin-1/2 Ising-Heisenberg and Heisenberg branched chains at triple and Kosterlitz-Thouless critical points.

The spin-1/2 Ising-Heisenberg branched chain composed of regularly alternating Ising spins and Heisenberg dimers involving an additional side branching is rigorously solved in a magnetic field by the transfer-matrix approach. The ground-state phase diagram, the magnetization process and the concurrence measuring a degree of bipartite entanglement within the Heisenberg dimers are examined in detail. Three different ground states were found depending on a mutual interplay between the magnetic field and two different coupling constants: the modulated quantum antiferromagnetic phase, the quantum ferrimagnetic phase, and the classical ferromagnetic phase. Two former quantum ground states are manifested in zero-temperature magnetization curves as intermediate plateaus at zero and one-half of the saturation magnetization, whereas the one-half plateau disappears at a triple point induced by a strong-enough ferromagnetic Ising coupling. The ground-state phase diagram and zero-temperature magnetization curves of the analogous spin-1/2 Heisenberg branched chain were investigated using density-matrix renormalization group calculations. The latter fully quantum Heisenberg model involves, besides two gapful phases manifested as zero and one-half magnetization plateaus, gapless quantum spin-liquid phase. The intermediate one-half plateau of the spin-1/2 Heisenberg branched chain vanishes at Kosterlitz-Thouless quantum critical point between gapful and gapless quantum ground states unlike the triple point of the spin-1/2 Ising-Heisenberg branched chain.

Detecting the Universal Fractional Entropy of Majorana Zero Modes.

A pair of Majorana zero modes (MZMs) constitutes a nonlocal qubit whose entropy is log2. Upon strongly coupling one of the constituent MZMs to a reservoir with a continuous density of states, a universal entropy change of 1/2log2 is expected to be observed across an intermediate temperature plateau. We adapt the entropy-measurement scheme that was the basis of a recent experiment by Hartman etal. [Nat. Phys. 14, 1083 (2018)10.1038/s41567-018-0250-5] to the case of a proximitized topological system hosting MZMs and propose a method to measure this 1/2log2 entropy change-an unambiguous signature of the nonlocal nature of the topological state. This approach offers an experimental strategy to distinguish MZMs from non topological states.

The gapless energy spectrum and spin-Peierls instability of 1D Heisenberg spin systems in polymeric complexes of transition metals and hypothetical carbon allotropes

We investigate the spin-Peierls instability of some periodic 1D Heisenberg spin systems having a gapless energy spectrum at different values of coupling J between the unit cells. Using the density-matrix renormalization group method we numerically study the dependence of critical exponents p of spin-Peierls transition of above spin systems on the value of J. In contrast to chain systems, we find significantly non-monotonous dependence p (J) for three-legs ladder system. In the limit of weak coupling J we derive effective spin s chain Hamiltonians describing the low-energy states of the system considered by means of perturbation theory. The value of site spin s coincides with the value of the ground-state spin of the isolated unit cell of the system considered. This means that at small J values all the systems with the singlet ground state and the same half-integer value of s should have a similar critical behavior which is in agreement with our numerical study. The presence of gapped excitations inside the unit cells at small values of J should give, for our spin systems, at least one intermediate plateau in field dependence of magnetization at low temperatures. The stability of this plateau against the increase of the values of J and temperature is studied using the quantum Monte-Carlo method.

Costal and crural diaphragm function during sustained hypoxia in awake canines.

In humans and other mammals, isocapnic hypoxia sustained for 20-60 min exhibits a biphasic ventilation pattern: initial increase followed by a significant ventilatory decline ("roll-off") to a lesser intermediate plateau. During sustained hypoxia, the mechanical action and activity of the diaphragm have not been studied; thus we assessed diaphragm function in response to hypoxic breathing. Thirteen spontaneously breathing awake canines were exposed to moderate levels of sustained isocapnic hypoxia lasting 20-25 min (80 ± 2% pulse oximeter oxygen saturation). Breathing pattern and changes in muscle length and electromyogram (EMG) activity of the costal and crural diaphragm were continuously recorded. Mean tidal shortening and EMG activity of the costal and crural diaphragm exhibited an overall biphasic pattern, with initial brisk increase followed by a significant decline (P < 0.01). Although costal and crural shortening did not differ significantly with sustained hypoxia, this equivalence in segmental shortening occurred despite distinct and differing EMG activities of the costal and crural segments. Specifically, initial hypoxia elicited a greater costal EMG activity compared with crural (P < 0.05), whereas sustained hypoxia resulted in a lesser crural EMG decline/attenuation than costal (P < 0.05). We conclude that sustained isocapnic hypoxia elicits a biphasic response in both ventilation and diaphragmatic function and there is clear differential activation and contribution of the two diaphragmatic segments. This different diaphragm segmental action is consistent with greater neural activation of costal diaphragm during initial hypoxia, then preferential sparing of crural activation as hypoxia is sustained. NEW & NOTEWORTHY In humans and other mammals, during isocapnic hypoxia sustained for 20-60 min ventilation exhibits a biphasic pattern: initial increase followed by significant ventilatory decline ("roll-off"). During sustained hypoxia, the function of the diaphragm is unknown. This study demonstrates that the diaphragm reveals a biphasic action during the time-dependent hypoxic "roll-off" in ventilation. These results also highlight that the two diaphragm segments, costal and crural, show differing, distinctive contributions to diaphragm function during sustained hypoxia.

Viscoelastic shear stress relaxation in two-dimensional glass-forming liquids

Translational dynamics of 2D glass-forming fluids is strongly influenced by soft, long-wavelength fluctuations first recognized by D. Mermin and H. Wagner. As a result of these fluctuations, characteristic features of glassy dynamics, such as plateaus in the mean-squared displacement and the self-intermediate scattering function, are absent in two dimensions. In contrast, Mermin-Wagner fluctuations do not influence orientational relaxation, and well-developed plateaus are observed in orientational correlation functions. It has been suggested that, by monitoring translational motion of particles relative to that of their neighbors, one can recover characteristic features of glassy dynamics and thus disentangle the Mermin-Wagner fluctuations from the 2D glass transition. Here we use molecular dynamics simulations to study viscoelastic relaxation in two and three dimensions. We find different behavior of the dynamic modulus below the onset of slow dynamics (determined by the orientational or cage-relative correlation functions) in two and three dimensions. The dynamic modulus for 2D supercooled fluids is more stretched than for 3D supercooled fluids and does not exhibit a plateau, which implies the absence of glassy viscoelastic relaxation. At lower temperatures, the 2D dynamic modulus starts exhibiting an intermediate time plateau and decays similarly to the 2D dynamic modulus. The differences in the glassy behavior of 2D and 3D glass-forming fluids parallel differences in the ordering scenarios in two and three dimensions.

Effects of quantitative composition of the sensing phase in the response of ionophore-based optical sensors

The response characteristics of the optical chemical sensors (optodes), namely response range, response span and sensitivity are quantitatively related to the composition of the sensor phase for the first time. The dependence of the characteristics of ion-selective bulk optodes on the concentrations of the indicator, ionophore and ionic additive (ion-exchanger) are simulated numerically and experimentally verified with Na+- and K+-selective colorimetric optodes. It is shown how the response span, response range, median and sensitivity depend on the sensor membrane composition. Response curves with an intermediate plateau are predicted theoretically and obtained experimentally. It is shown that the inflection point in the response curve does not necessarily refers to α = 0.5. The results can be used for the fine tuning of the optical response of chemical sensors.

Integrated Geophysical-Geological 3D Model of the Right-Bank Slope Downstream from the Rogun Dam Construction Site, Tajikistan

In summer of 2015 we had completed a geophysical survey complemented by borehole drilling near the right-bank slope of the Rogun Dam construction site, Tajikistan. These data were first processed and then compiled within a 3D geomodel. The present paper describes the geophysical results and the 3D geomodel generated for an ancient mass movement located immediately downstream from the construction site. The geophysical survey included electrical and seismic profiles and ambient vibration measurements as well as earthquake recordings. The electrical and seismic data were processed as tomographic sections, the ambient vibrations as horizontal-to-vertical spectral H/V ratios, and the earthquake data mainly in terms of standard spectral ratios. By estimating the average shear wave velocities of the subsurface, we computed the local soft layer thickness from the resonance frequencies revealed by the H/V ratios. Three seismic stations had been installed for ten days along a profile crossing the intermediate plateau. Standard spectral ratios inferred from ten processed earthquake measurements confirmed the presence of a thick soft material layer on the plateau made of weathered rocks, colluvium, and terrace deposits, which produce a medium-level amplification at about 2 Hz. The 3D geomodel was first built on the basis of new topographic data, satellite imagery, and a geological map with two sections. Then, the various electrical resistivity and seismic refraction tomographies were inserted in the geomodel. The soft layer thickness information and borehole data were represented in terms of logs in the model. The site is crossed by the Ionakhsh Fault that could be modeled on the basis of the geological inputs and of a lateral resistivity gradient found on one electrical profile along the steep lower slope. The integrated interpretation of all results reveals that probably only a relatively small part of the ancient giant mass movement is really exposed to slope instability phenomena.

Structural origin of dynamical relaxation in undercooled Cu50Zr50 metallic liquid

Molecular dynamics (MD) simulation has been performed to explore the correlation between dynamic characteristics and structural heterogeneity in undercooled Cu50Zr50 melt based on the embedded atom method. It is found that atoms in the undercooled liquid can be classified into three groups in terms of the probability distribution of atoms' displacement, named ‘fast atoms’ (FAs), ‘intermediate atoms’ (IAs), ‘slow atoms’ (SAs). Meanwhile, the undercooled liquid can be divided into three temperature regime: as the temperature is higher than 1120 K, the distribution of FAs become network connectivity, in which the SAs region are surrounded; as the temperature is in the range from 1120 K to 900 K, the network of FAs region decompose into several isolated region gradually; after that the single relaxation separates into α- and β-relaxation at temperature lower than 900 K, the FAs region become isolated islands, while the SAs have connected into networks where the FAs regions are surrounded, which cause the significant decreasing of atomic mobility and sharp increasing of the relaxation time. The FAs, located in loose packaging and isolated region, which corresponds to β-relaxation reflected by the time-scale of intermediate plateau in mean-squared displacement (MSD) and intermediate scattering function (ISF). The SAs which develop into the backbone of the system and surround clusters formed by FAs, are responsible for the glass formation and have a connection with α-relaxation. The compressive deformation in the Cu50Zr50 metallic glass shows that the ‘fast atoms’, anticipating in β-relaxation of undercooled liquid, mostly are located in large shear strain zones and the structural heterogeneity of undercooled liquid inherits into the glass. Since metallic glass (MG) can be regarded as frozen undercooled liquid, our study is helpful for understanding the structural origins of dynamical relaxation in MGs.

Stepped Propane Adsorption in Pure-Silica ITW Zeolite.

Gas adsorption over zeolites is at the basis of important applications of this class of microporous crystalline solids, notably as separation media and catalysts, but it may also be complex and not straightforward to understand. Here we report that for temperature below 323 K propane adsorption on the small-pore pure-silica zeolite ITW exhibits a clear step (pseudosaturation). This is absent in the case of propene and the other small linear alkanes. An intermediate plateau, clearly observed in the 293 K isotherm, always occurs when one molecule of propane is loaded in every other cage, i.e., at half-saturation. The simulation results show a swelling of the ITW structure upon propane adsorption. The strong dependence of available pore volume on the adsorbate loading level implies that adsorption cannot occur on the void structure while saturation can only be reached on highly loaded structures. To account for this unprecedented adsorption phenomenon, we propose the term "guest-modulated effect".

Crystallization behavior of polymer-derived Si-O-C for ceramic matrix composite processing

To facilitate the development of matrix processing protocols for SiC-based ceramic matrix composites (CMC) using the polymer infiltration and pyrolysis (PIP), the crystallization behavior of a commercial Si-(O)-C polymer derived ceramic (PDC) was studied using fiberless matrix monoliths replicating the microstructure features common in PIP CMC matrices. The study examined how the processing time and temperature impact the apparent bulk (average) crystallinity as well as how microstructure features lead to variations in the local crystallization rates. The first stage of crystallization involves rapid β-SiC precipitation throughout the bulk of the material. This stage appears to be insensitive to the local microstructure. Subsequent crystallization stages involve partial decomposition of PDC, producing CO and/or SiO. Because these processes involve gaseous exchange with the atmosphere, they are more directly influenced by the local microstructure. Therefore, although the bulk crystallinity quickly reaches an intermediate plateau corresponding to partial phase separation, the near-surface regions are fully crystallized more quickly than the interior regions. The implications of these effects are discussed in the context of the processing and performance of SiC-CMCs.

Echoes of Kerr-like wormholes

Structure at the horizon scale of black holes would give rise to echoes of the gravitational wave signal associated with the post-merger ringdown phase in binary coalescences. We study the waveform of echoes in static and stationary, traversable wormholes in which perturbations are governed by a symmetric effective potential. We argue that echoes are dominated by the wormhole quasinormal frequency nearest to the fundamental black hole frequency that controls the primary signal. We put forward an accurate method to construct the echoes waveform(s) from the primary signal and the quasinormal frequencies of the wormhole, which we characterize. We illustrate this in the static Damour-Solodukhin wormhole and in a new, rotating generalization that approximates a Kerr black hole outside the throat. Rotation gives rise to a potential with an intermediate plateau region that breaks the degeneracy of the quasinormal frequencies. Rotation also leads to late-time instabilities which, however, fade away for small angular momentum.

Abnormal shapes of production function: Model interpretations

An abnormal non-monotonic shape of production function (response of obtained yield to increasing rates of mineral nitrogen fertilizers) has been observed in experimental field trials. Often, the observed effect (an inflection point, or intermediate plateau or even local undershoot of the “yield-fertilization” curve) is treated as a test distortion and will be ignored or sorted out. This article presents the authors’ efforts to interpret and to explain similar phenomenon by means of investigating two mechanistic crop simulation models – AGROSIM and AGROTOOL. It is demonstrated that an imitation model can be used as a valuable tool of scientific research, allowing for the hypothesising of alternative understandings of non-trivial natural phenomena.

Association of diurnal temperature range with daily mortality in England and Wales: A nationwide time-series study

BackgroundDiurnal temperature range (DTR) reflects within-day temperature variability and is closely associated with climate change. In comparison to temperature extremes, up-to-date DTR-health evidence at the regional and national scales has been still very limited worldwide, especially in Europe. ObjectivesThis study aimed to provide nationwide estimates for DTR-associated effects on mortality, and explore whether season and regional-level characteristics modify DTR-mortality relation in United Kingdom. MethodsFourteen-year time-series data on weather and mortality were collected from 10 regions in England and Wales during 1993–2006, including 7,573,716 total deaths. A quasi-Poisson regression incorporated with distributed lag non-linear model was first applied to estimate region-specific DTR-mortality relationships. Then, a multivariate meta-analysis was employed to derive the pooled DTR effects at the national level. Also, the modifying effects of some regional characteristics (e.g., geographical and climatological) were examined by conducting multivariate meta-regression. ResultsA non-linear DTR-mortality relationship was identified in UK. At the national level, increasing DTR raised the mortality risk observably when DTR exposure was below 25th percentile or above 90th percentile of DTR distribution, with an intermediate risk plateau indicating no associations. Extremely high DTR exhibited greater adverse effect estimates in hot season compared with in cold and transitional season, whereas entirely different association patterns were observed for the season-specific effects of extremely low DTR. In addition to season, regional latitudes, average temperature and humidity were also found to significantly modify DTR-mortality relationship. ConclusionsOur study added strong evidence that extremely high DTR increased short-term mortality, whereas the effects of extremely low DTR exhibited entirely different seasonal patterns. Also, mortality vulnerability to DTR extremes varied greatly by regional latitudes and climate conditions.

Spin-State Patterning in an Iron(II) Tripodal Spin-Crossover Complex.

A mononuclear iron(II) complex that displays a gradual two-step spin-crossover (SCO) transition is reported. The intermediate plateau (IP) occurs between HS0.40LS0.60 and HS0.30LS0.70 (HS = high spin; LS = low spin) ratios over the region of ca. 190–170 K. A phase change occurs at the IP, breaking the symmetry, resulting in six independent SCO sites compared to one at the 100% HS and LS plateau regions, respectively. Variable-temperature X-ray photoelectron spectroscopy shows that the SCO behavior is completely reversible among the HS, IP, and LS regions. The results both confirm and extend the related results for the above system described by Halcrow et al. (KulmaczewskiR.; CespedesO.; HalcrowM. A.Gradual Thermal Spin-Crossover Mediated By a Reentrant Z′ = 1 → Z′ = 6 → Z′ = 1 Phase Transition, Inorg. Chem. 2017, 56, 3144−314828244751) in a recent report.

Thermal decomposition of heavy rare-earth butanoates, Ln(C3H7CO2)3 (Ln = Er, Tm, Yb and Lu) in argon

The thermal behaviour of Ln(C3H7CO2)3 (Ln = Er, Tm, Yb or Lu) was studied in argon from room temperature by means of thermogravimetry and differential thermal analysis up to 1400 °C, by infrared spectroscopy, hot-stage optical microscopy and X-ray diffraction. Melting prior to decomposition was observed in all four compounds, but its course depends on the rare-earth element. Decomposition to sesquioxides proceeds via the formation of dioxymonocarbonates (Ln2O2CO3) and release of 4-heptanone (C3H7COC3H7) as well as carbon dioxide (CO2) without evidence for an intermediate oxobutanoate stage. During the decomposition of Ln2O2CO3 into the respective sesquioxides (Ln2O3), an intermediate plateau extending from approximately 550 to 850 °C appears in the TG traces. The overall composition during this stage corresponds approximately to Ln2O2.8(CO3)0.2, but the state is more probably a mixture of Ln2O2CO3 and Ln2O3. The stability of this intermediate state seems to decrease with the mass of the rare-earth elements. Complete conversion to Ln2O3 is reached at about 1100 °C. The overall thermal decomposition behaviour of the title compounds is different from previous reports for other rare-earth butanoates.

Breakdown of a Magnetization Plateau in Ferrimagnetic Mixed Spin-(1/2,S) Heisenberg Chains due to a Quantum Phase Transition towards the Luttinger Spin Liquid

Magnetization curves of the ferrimagnetic mixed spin-(1/2,S) Heisenberg chains are calculated with the help of density-matrix renormalization group method for several quantum spin numbers S=1, 3/2, 2 and 5/2. It is shown that the ferrimagnetic mixed spin-(1/2,S) Heisenberg chains exhibit irrespective of the spin value S exactly one intermediate magnetization plateau, which can be identified with the gapped Lieb-Mattis ferrimagnetic ground state. The magnetization plateau due to the Lieb-Mattis ferrimagnetism breaks down at a quantum phase transition towards the Luttinger spin liquid, which is characterized by a continuous change of the magnetization with the magnetic field until another quantum critical point is reached at the saturation field.

Na1+XFexTi2-X(PO4)3/C (x = 0-1) Electrode Materials for Na-Ion Batteries

Lithium resources are unevenly distributed worldwide and might not meet the increasing global demand for energy. Rechargeable Na-ion batteries can be considered as a serious alternative due to the natural abundance and the low cost of sodium especially for electrical energy storage associated with the deployment of sustainable and renewable energy sources. In addition, aqueous electrolytes improves the safety of the batteries and are environmentally benign. Thus, there is an increasing interest in the research of new electrode materials that can be used in such systems. Transition metal phosphates with NASICON structure are good candidates due to their high ionic conductivity and the possibility of tuning the potential by selecting the transition metal. However, they present low electronic conductivity that require doping, nanostructuration or coating to improve electrochemical performances. Na1+xFexTi2-x(PO4)3/C composites, with x=0-1, could be used as anode or cathode materials for Na-ion batteries since they exhibit three different potential plateaus at 4 V, 2.2 V and 0.4 V vs. Na+/Na0 depending on the amount of inserted Na+. These composite materials were obtained by solid state reaction with sucrose as carbon source for conductive coating and were characterized by different experimental and theoretical methods (Figure 1). The electrochemical mechanisms were identified from operando techniques, especially for the intermediate potential plateau at 2.2 V vs. Na+/Na0 that is related to changes in the oxidation states of both Ti and Fe. For example, the reduction of Fe3+ into Fe2+ was observed at the beginning of the discharge from 57Fe Mössbauer spectroscopy. High electrochemical performances were obtained at this potential including long cycle lifetime, high specific capacity and high power rate that are explained by the morphology of the particles, the carbon coating and the substitution of Fe for Ti (Figure 2). Acknowledgments Financial supports by Campus France (PHC Toubkal 008/SM/13), the Centre National de la Recherche Scientifique (CNRS, France), the Centre National de la Recherche Scientifique et Technique (CNRST, Maroc), the Institut de Recherche en Energie Solaire et en Energies Nouvelles (IRESEN, Maroc), the Swedish Research Council (contract 2012-3392) and StandUp for Energy (Sweden) are gratefully acknowledged. Figure 1

Experimental Investigations Into Pulse-Charged Spark Gap Recovery Times and Influencing Factors

The spark gap switch is the key element in any pulsed power system, which directly determines the pulse repetitive frequency of the system. The dielectric recovery data of the spark gap play a basic role, but they have not yet been adequately studied for repetitive pulse charge conditions. This paper describes some of the factors that affect the recovery of spark gap switch for pulse-charged operation. A two-pulse technique has been used, in which the first pulse is applied to the spark gap to overvolt the gap and initiate the breakdown and the second pulse is used to determine the recovery voltage of the gap. The effects of electrode size, pulse rise time, and conduction current on the spark gap recovery performance are presented. Experiments were performed by using a double-pulse generator capable of generating 40-kV pulses with a delay of 1 ms–1 s. Spark gap electrodes of 34-, 40-, and 68-mm diameters and a point type were used in the study. The effect of voltage rise rate was studied by changing the charging capacitor to 100, 500, and 1000 nF in the circuit. An intermediate plateau was observed in the spark gap recovery curves. In addition, an increase in the output impedance resulted in a decrease in the time taken for the recovery of the spark gap. Also, the switch recovery appears to be largely dependent on the electrode shape and size compared with the pulse rise time.