Structural Degrees Of Freedom Research Articles

Large voltage-induced coercivity change in Pt/Co/CoO/amorphous TiOx structure and heavy metal insertion effect

There is urgent need for spintronics materials exhibiting a large voltage modulation effect to fulfill the great demand for high-speed, low-power-consumption information processing systems. Fcc-Co (111)-based systems are a promising option for research on the voltage effect, on account of their large perpendicular magnetic anisotropy (PMA) and high degree of freedom in structure. Aiming to observe a large voltage effect in a fcc-Co (111)-based system at room temperature, we investigated the voltage-induced coercivity (Hc) change of perpendicularly magnetized Pt/heavy metal/Co/CoO/amorphous TiOx structures. The thin CoO layer in the structure was the result of the surface oxidation of Co. We observed a large voltage-induced Hc change of 20.2 mT by applying 2 V (0.32 V/nm) to a sample without heavy metal insertion, and an Hc change of 15.4 mT by applying 1.8 V (0.29 V/nm) to an Ir-inserted sample. The relative thick Co thickness, Co surface oxidation, and large dielectric constant of TiOx layer could be related to the large voltage-induced Hc change. Furthermore, we demonstrated the separate adjustment of Hc and a voltage-induced Hc change by utilizing both upper and lower interfaces of Co.

Magnetism and Its Structural Coupling Effects in 2D Ising Ferromagnetic Insulator VI3.

van der Waals (vdW) magnets have emerged as a tunable platform for exploring a variety of layer-dependent magnetic phenomena. Here we probe the thickness-dependent magnetism of vanadium triiodide (VI3), a material known as a layered ferromagnetic Mott insulator in its bulk form, using magnetic circular dichroism microscopy. Robust ferromagnetism is observed in all thin layers, down to the monolayer limit with large coercive fields. In contrast to known vdW magnets, the Curie temperature shows an anomalous increase as the layer number decreases, reaching a maximum of 60 K in monolayers. Second harmonic generation measurements reveal broken inversion symmetry in exfoliated flakes, down to trilayers. This observation demonstrates that the exfoliated flakes take a layer stacking arrangement that differed from the inversion-symmetric parent bulk counterpart. Our results suggest a coupling effect between magnetic and structural degrees of freedom in VI3 and its potential for engineering layer and twist angle-dependent magnetic phenomena.

Quantum coherent spin–electric control in a molecular nanomagnet at clock transitions

Electrical control of spins at the nanoscale offers significant architectural advantages in spintronics, because electric fields can be confined over shorter length scales than magnetic fields. Thus, recent demonstrations of electric-field (E-field) sensitivities in molecular spin materials are tantalising, raising the viability of the quantum analogues of macroscopic magneto-electric devices.However, the E-field sensitivities reported so far are rather weak, prompting the question of how to design molecules with stronger spin-electric couplings. Here we show that one path is to identify an energy scale in the spin spectrum that is associated with a structural degree of freedom with a significant electrical polarisability. We study an example of a molecular nanomagnet in which a small structural distortion establishes clock transitions (i.e. transitions whose energy is to first order independent of magnetic field) in the spin spectrum; the fact that this distortion is associated with an electric dipole allows us to control the clock transition energy to an unprecedented degree. We demonstrate coherent electrical control of the quantum spin state and exploit it to manipulate independently the two magnetically-identical but inversion-related molecules in the unit cell of the crystal. Our findings pave the way for the use of molecular spins in quantum technologies and spintronics.

Effects of seismic input, fine crust and existing structure on liquefaction from centrifuge model tests

The results of dynamic centrifuge tests carried out to study the effects of seismic input, fine crust and existing structure on liquefaction triggering and manifestations are presented. The basic concept of the experimentation was to analyse the seismic behaviour of level ground, saturated, 14 m deep sandy deposits, homogeneous or stratified, subjected to increasing seismic excitations up to liquefaction, with or without a one degree of freedom structure on shallow foundations. The study was performed in the framework of the European project Horizon2020 “LIQUEFACT”.

Mass enhancement in 3d and s−p perovskites from symmetry breaking

In some d-electron oxides the measured effective mass m(exptl) has long been known to be significantly larger than the model effective mass m(model) deduced from mean-field band theory, i.e., m(exptl) = beta * m(model), where beta > 1 is the "mass enhancement", or "mass renormalization" factor. Previous applications of density functional theory (DFT), based on the smallest number of possible magnetic, orbital, and structural degrees of freedom, missed such mass enhancement, a fact that was taken as evidence of strong electronic correlation being the exclusive enabling physics. The current paper reports that known modalities of energy-lowering symmetry-broken spin and structural effects included in mean-field DFT show mass enhancement for both electrons and holes in a range of d-electron perovskites SrVO3, SrTiO3, BaTiO3, and LaMnO3 as well as p-electron perovskites CsPbI3 and SrBiO3, including metals (SrVO3) and insulators (the rest). This is revealed only when enlarged unit cells of the same parent global symmetry, which are large enough to allow for symmetry breaking distortions and concomitant variations in spin order, are explored for their ability to lower the total energy. The paper analyzes the contributions of different symmetry-broken modalities to mass enhancement, finds common effects in the range of d- as well as p-electron perovskites. Thus, symmetry breaking in mean-field theory could describe effects that were previously attributed exclusively to complex correlated treatments. Indeed, broken symmetries are often experimentally observed, e.g., octahedral tilting, Jahn-Teller distortions, or bond disproportionation, and often provide intuitive explanations in terms of degeneracy removal due to lowering of structural symmetry, or as shifting of band energies in explainable directions.

Universal prediction of strain footprints via simulation, statistics, and machine learning: low-Σ grain boundaries

Interface engineering usually imposes a trade-off between catalytic activity, product selectivity, and property tunability, facilitating multiple product yields. Due to their structural disorder, metal grain boundaries (GBs) can be constructed to satisfy all of these conditions. Though experiments show GB catalytic footprints are determined by dislocation-induced elastic strain, the atomistic structural and energetic origins of GB catalytic performance are not currently known. In former models solely reviewing metastable GBs defined by macroscopic degrees of freedom (DOFs), exceptional low-Σ GBs anticipated by the coincident site lattice model cannot be consistently discerned. Herein, a structure-energy correlation linking changes in atomistic properties to physical models is developed, distinguishing exceptional GBs from unexceptional high-angle GBs over structural DOFs. This work constructs particular GB elastic responses by varying three microscopic DOFs, comparing low-Σ distinguished and other GB responses via a directed statistical approach. Such elastic properties successfully distinguish low-Σ GBs from high-angle grain boundaries (HAGBs) by their strain-related footprints without failure of a single unique GB structure and composition combination. A priori application of machine learning classification is completed using metastable GB and elastic response related properties. This classification not only validates distinguished strain footprints, but also identifies GB subgroups with footprints unexpected by former models.

Identification of materials with strong magnetostructural coupling using computational high-throughput screening

Important phenomena such as magnetostriction, magnetocaloric, and magnetoelectric effects arise from, or could be enhanced by, the coupling of magnetic and structural degrees of freedom. The coupling of spin and lattice also influence transport and structural properties in magnetic materials, in particular around phase transitions. In this paper we propose a method for screening materials for a strong magnetostructural coupling by assessing the effect of the local magnetic configuration on the atomic forces using density functional theory. We have employed the disordered local moment approach in a supercell formulation to probe different magnetic local configurations and their forces and performed a high-throughput search on binary and ternary compounds available in the Crystallography Open Database. We identify a list of materials with a strong spin-lattice coupling out of which several are already known to display magnetolattice coupling phenomena such as ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ and CrN. Others, such as ${\mathrm{Mn}}_{2}{\mathrm{CrO}}_{4}$ and $\mathrm{Ca}{\mathrm{Fe}}_{7}{\mathrm{O}}_{11}$, have been less studied and have yet to reveal their potentials in experiments and applications.

Research Progress of Exoskeleton for Hand Rehabilitation following stroke

Based on the hand rehabilitation exoskeleton, the research results of three driving modes in recent years, namely cable, connecting rod and pneumatic system, were classified, summarized and analyzed. Through research and analysis, the results of structural dimensions, structural degrees of freedom, drive selection scheme, control strategy and sensor selection scheme which are more suitable for human hand rehabilitation exoskeleton are obtained, which can provide reference for exoskeleton researchers.

Plasmonic and label-free real-time quantitative PCR for point-of-care diagnostics.

In response to the world's medical community's need for accurate and immediate infectious pathogen detection, many researchers have focused on adapting the standard molecular diagnostic method of polymerase chain reaction (PCR) for point-of-care (POC) applications. PCR technology is not without its shortcomings; current platforms can be bulky, slow, and power-intensive. Although there have been some advances in microfluidic PCR devices, a simple-to-operate and fabricate PCR device is still lacking. In the first part of this paper, we introduce a compact plasmonic PCR thermocycler in which fast DNA amplification is derived from efficient photothermal heating of a colloidal reaction mixture containing gold nanorods (AuNRs) using a small-scale vertical-cavity surface-emitting laser (VCSEL). Using this method, we demonstrate 30 cycle-assay time of sub-ten minutes for successful Chlamydia trachomatis DNA amplification in 20 μL total PCR sample volume. In the second part, we report an ultrasensitive real-time amplicon detection strategy which is based on cycle-by-cycle monitoring of 260 nm absorption of the PCR sample. This was accomplished by irradiating the PCR sample using a UV LED and collecting the transmitted optical power with a photodetector. The UV absorption dependency on the nucleotides' structural degree of freedom gives rise to distinctive features in the shape of UV amplification curves for the determination of PCR results, thus circumventing the need for the complicated design of target-specific probes or intercalating fluorophores. This amplicon quantification method has a high detection sensitivity of one DNA copy. This is the first demonstration of a compact plasmonic thermocycler combined with a real-time fluorophore-free quantitative amplicon detection system. The small footprint of our PCR device stems from hardware miniaturization, while abundant sample volume facilitates highly sensitive detection and fluid handling required for in-field sample analysis, thereby making it an excellent candidate for POC molecular diagnostics.

Monitoring molecular vibronic coherences in a bichromophoric molecule by ultrafast X-ray spectroscopy.

The role of quantum-mechanical coherences in the elementary photophysics of functional optoelectronic molecular materials is currently under active study. Designing and controlling stable coherences arising from concerted vibronic dynamics in organic chromophores is the key for numerous applications. Here, we present fundamental insight into the energy transfer properties of a rigid synthetic heterodimer that has been experimentally engineered to study coherences. Quantum non-adiabatic excited state simulations are used to compute X-ray Raman signals, which are able to sensitively monitor the coherence evolution. Our results verify their vibronic nature, that survives multiple conical intersection passages for several hundred femtoseconds at room temperature. Despite the contributions of highly heterogeneous evolution pathways, the coherences are unambiguously visualized by the experimentally accessible X-ray signals. They offer direct information on the dynamics of electronic and structural degrees of freedom, paving the way for detailed coherence measurements in functional organic materials.

Structural damage identification based on fast S-transform and convolutional neural networks

Measured signals from installed sensors on structures cannot solely provide beneficial information about the presence of damage. Many signal processing methods have been developed to extract useful data from raw signals. However, each method has its advantages and disadvantages. In the present study, the fast S-transform signal processing method has been used for the damage detection of structures. Fast S-transform outperforms traditional S-Transform since it filters out unusable data using a scaling method. The method’s performance in obtaining correct natural frequencies of a structure has been evaluated using a 2 Degrees of Freedom (DOF) mass-spring dynamic system. Additionally, the ability of the method to detect damages in structural systems has been demonstrated using a 6 DOF structure subjected to Northridge earthquake record. The results of the mentioned numerical studies show that the fast S-transform can extract the accurate resonance frequencies of a structure, and also can detect the presence and the time of damage occurrence. In the experimental study, a 3 story plexi frame has been excited by a chirp sinusoidal signal. Furthermore, four different damage scenarios have been defined in the experimental study. To classify the four damage types, Convolutional Neural Network (CNN) has been used. The results of the experimental study show that fast S-transform can detect damages in real-time monitoring of structures, and the classification using CNN can identify the severity of damage.

Structural and physical properties of trilayer nickelates R4Ni3O10 ( R=La , Pr, and Nd)

We investigate the low temperature structural and physical properties of the trilayer nickelates R4Ni3O10 (R = La, Pr and Nd) using resistivity, thermopower, thermal conductivity, specific heat, high-resolution synchrotron powder X-ray diffraction and thermal expansion experiments. We show that all three compounds crystallize with a monoclinic symmetry, and undergo a metal-to-metal (MMT) transition at 135 K (La), 156 K (Pr) and 160 K (Nd). At MMT, the lattice parameters show distinct anomalies; however, without any lowering of the lattice symmetry. Unambiguous signatures of MMT are also seen in magnetic and thermal measurements, which suggest a strong coupling between the electronic, magnetic and structural degrees of freedom in these nickelates. Analysis of thermal expansion yields hydrostatic pressure dependence of MMT in close agreement with experiments. We show that the 9-fold coordinated Pr ions in the rocksalt (RS) layers have a crystal field (CF) split doublet ground state with possible antiferromagnetic ordering at 5 K. The Pr ions located in the perovskite block (PB) layers with 12-fold coordination, however, exhibit a non-magnetic singlet ground state. The CF ground state of Nd in both RS and PB layers is a Kramers doublet. Heat capacity of R = Nd shows a Schottky-like anomaly near35 K, and an upturn below T = 10 K suggesting the presence of short-range correlations between the Nd moments. However, no signs of long-range ordering could be found down to 2 K despite a sizeable theta_p ~ -40 K. The strongly suppressed magnetic long-range ordering in both R = Pr and Nd suggests the presence of strong magnetic frustration in these compounds. The low-temperature resistivity shows a T^0.5 dependence. No evidence for the heavy fermion behavior could be found in any of the three compounds.

Hexagon-Twist Frequency Reconfigurable Antennas via Multi-Material Printed Thermo-Responsive Origami Structures

The origami structure has caused a great interest in the field of engineering, and it has fantastic applications in the deployable and reconfigurable structures. Owing to the unique multi-stable states, here a typical hexagon-twist origami structure is fabricated via multi-material printing technology. The printed structure has multi-stable features and the stiffness of the deformable structure is dramatically reduced under thermal triggering. Such behavior causes an increase in the structural degree of freedom, allowing for self-deployment via releasing the prestored energy in the elastic crease. The response time and reaction time of the self-deployment process are also studied and illustrate the higher energy barrier of the folded state, the longer self-deployment time. Utilizing such unique features and design principles, a prototype of frequency reconfigurable origami antenna of nine diverse operating modes is subsequently designed and assembled with the hexagon-twist origami structure as the dielectric substrate. The antenna implements the cross-band from two different frequency bands, enabling to realize frequency reconfigurable under thermal condition.

Optical properties of LaNiO3 films tuned from compressive to tensile strain

Materials with strong electronic correlations host remarkable -- and technologically relevant -- phenomena such as magnetism, superconductivity and metal-insulator transitions. Harnessing and controlling these effects is a major challenge, on which key advances are being made through lattice and strain engineering in thin films and heterostructures, leveraging the complex interplay between electronic and structural degrees of freedom. Here we show that the electronic structure of LaNiO3 can be tuned by means of lattice engineering. We use different substrates to induce compressive and tensile biaxial epitaxial strain in LaNiO3 thin films. Our measurements reveal systematic changes of the optical spectrum as a function of strain and, notably, an increase of the low-frequency free carrier weight as tensile strain is applied. Using density functional theory (DFT) calculations, we show that this apparently counter-intuitive effect is due to a change of orientation of the oxygen octahedra.The calculations also reveal drastic changes of the electronic structure under strain, associated with a Fermi surface Lifshitz transition. We provide an online applet to explore these effects. The experimental value of integrated spectral weight below 2 eV is significantly (up to a factor of 3) smaller than the DFT results, indicating a transfer of spectral weight from the infrared to energies above 2 eV. The suppression of the free carrier weight and the transfer of spectral weight to high energies together indicate a correlation-induced band narrowing and free carrier mass enhancement due to electronic correlations. Our findings provide a promising avenue for the tuning and control of quantum materials employing lattice engineering.

Numerical Investigation of a New Method for Seismic Control of Structures

Vertical mass isolation (VMI) method is used for the seismic control of structures. In this method, the entire structure is considered to be a combination of two mass and stiffness subsystems with an isolator layer located in-between. A magnetorheological (MR) damper is used as the isolator layer to control the structure. The semi-active control technique is applied to control the MR damper based on the applied controlling voltage. Several single degree of freedom structures with the same masses and main periods of 0.5, 1.0, 2.0 and 3.0 seconds are studied. Finally, a comparison between the results of this method with three passive control methods was performed. Results indicated that the semi-active control method based on maximum voltage of 9V will reduce, on average, the maximum roof displacement by 25% and 51% more than the Copt and passive-off methods and is equal to the passive-on method at 9V. However, the efficiency of the semi-active method in controlling the maximum absolute acceleration of the roof and the base shear of the structure was on average 28% and 45% lower than the Copt and passive-off methods, respectively and 2% higher than the passive-on method.

Hydrostatic and Uniaxial Pressure Tuning of Iron‐Based Superconductors: Insights into Superconductivity, Magnetism, Nematicity, and Collapsed Tetragonal Transitions

AbstractIron‐based superconductors are well‐known for their intriguing phase diagrams, which manifest a complex interplay of electronic, magnetic, and structural degrees of freedom. Among the phase transitions observed are superconducting, magnetic, and several types of structural transitions, including a tetragonal‐to‐orthorhombic and a collapsed‐tetragonal transition. In particular, the widely observed tetragonal‐to‐orthorhombic transition is believed to be a result of an electronic order that is coupled to the crystalline lattice and is, thus, referred to as nematic transition. Nematicity is therefore a prominent feature of these materials, which signals the importance of the coupling of electronic and lattice properties. Correspondingly, these systems are particularly susceptible to tuning via pressure (hydrostatic, uniaxial, or some combination). Efforts to probe the phase diagrams of pressure‐tuned iron‐based superconductors are reviewed with a strong focus on recent insights into the phase diagrams of several members of this material class under hydrostatic pressure. These studies on FeSe, Ba(FeCox)2As2, Ca(FeCox)2As2, and CaK(FeNix)4As4are, to a significant extent, made possible by advances of what measurements can be adapted to their use under differing pressure environments. The potential impact of these tools for the study of the wider class of strongly correlated electron systems is pointed out.

Enhancing giant magnetocaloric effect near room temperature by inducing magnetostructural coupling in Cu-doped MnCoGe

High performance magnetocaloric materials are crucial to realize the energy efficient and environment friendly magnetic cooling/refrigeration technology. We have designed Mn1-xCuxCoGe compounds possessing a giant magnetocaloric effect near room temperature. The magnetic and structural degree of freedom have been coupled by substituting Cu for Mn leading to a first-order magnetostructural phase transformation resulting in a giant magnetocaloric effect over a wide temperature window of 100 K (250–350 K). A very large entropy change value of 58 J.kg−1.K−1 corresponding to a magnetic field change of 5 T near room temperature has been obtained for Mn0.89Cu0.11CoGe exhibiting a maximum effective refrigerant capacity of 258.2 J.kg−1. The first-order magnetostructural phase transformation which is essential for the giant magnetocaloric effect has been confirmed by a combinatorial master-curve and Arrott-plot analyses. The results of giant magnetocaloric effect realized in Mn1-xCuxCoGe are comparable to or better than that of the other reported high performing materials, and this material can be of significant importance for the development of environment friendly and energy efficient cooling devices. The approach of magnetostructural coupling by tuning the structural and magnetic transitions for a giant magnetocaloric effect can also be adopted for other materials to design the best solid-state magnetic refrigerant.

Active vibration control in a two degrees of freedom structure using piezoelectric transducers associated with negative capacitance shunt circuits

The need for control or suppression of vibrations in mechanical structures has arisen because of their damaging effects on people, civil structures and machine parts. The present work aims to perform the vibration control of a portico type structure with two degrees of freedom, using piezoelectric transducers associated with negative capacitance shunt circuits with series electrical resistance. For this purpose, an electronic circuit with passive and active components associated with piezoelectric transducers QP10W was developed to produce a negative capacitance shunt circuit, implemented through Negative Impedance Converters (NIC) and using operational amplifiers. The response amplitudes of the system in the time domain and the frequency in free and forced vibration were analyzed in tests performed with and without shunt circuit operation in the system. Considering free vibration, a reduction of 9.01 dB was obtained for the first natural frequency and of 6.95 dB for the second one. For forced vibration, reductions of 1.5 dB were obtained for the first natural frequency and 2.19 dB for the second natural frequency, respectively. The vibration reductions obtained with the proposed system demonstrate the efficiency of the system.

Projectile breakup effects in the fusion dynamics of 6,7Li +144,152Sm reactions around Coulomb barrier

This work emphasized the role of the projectile breakup channel by studying the complete fusion (CF) and incomplete fusion (ICF) dynamics of [Formula: see text] reactions. The theoretical calculations for the chosen reactions have been done by opting for the coupled channel approach and the energy dependent Woods–Saxon potential (EDWSP) model. The below barrier fusion enhancements of the studied reactions are reasonably addressed by the outcomes of the adopted models, which in turn can be attributed to the couplings of nuclear structure degrees of freedom of the collision partners to their relative motion. In contrast, at above barrier energies, the CF cross-section data of the chosen reactions are found to be suppressed significantly when compared with the predictions made by using the present models. Interestingly, the fusion suppression factors of the given reactions can be minimized considerably with respect to the reported value when it is analyzed within the framework of the EDWSP model. For instance, in case of [Formula: see text] ([Formula: see text] reaction, the magnitude of fusion suppression factor is minimized up to 7% (13%) relative to the reported value whereas for [Formula: see text] ([Formula: see text] reaction, the fusion suppression factor is found to be less by 7% (8%) with reference to the reported value. Such suppression effects can be correlated with the low breakup threshold of alpha breakup channel associated with the loosely bound projectile. The projectiles being weakly bound systems split into two charged fragments and either of the breakup components is absorbed by the target resulting in the reduction of incoming flux going into fusion channel. The flux lost from the CF channel appears in the form of ICF yields. For [Formula: see text], total fusion (TF) cross-sections that are sum of CF and ICF cross-sections are also analyzed in conjunction with the EDWSP model and thus reasonably explained by the model calculations. In order to identify the ICF contribution, the ratio of ICF/TF cross-section data of [Formula: see text] reaction has been examined and thus properly addressed by using the EDWSP model. The presence of ICF component in TF cross-section clearly pointed out the breakup of projectile due to its loosely bound nature prior to the Coulomb barrier. Although ICF data of other systems are not available in the literature, a similar behavior is expected for ICF and TF data for [Formula: see text] and [Formula: see text] reactions.

Optimal arrangement of structural sensors in soft rock tunnels based industrial IoT applications

In recent years, with the rapid development of China’s economy, many civil engineering structures such as high-rise buildings, bridges, dams and tunnel have increased rapidly. Sensor optimization layout, as an important technology of Structural Health Monitoring (SHM), has become one of the research hotspots in related fields and disciplines. Due to the limitations of civil engineering structures and real economic conditions, it is not possible to place sensors on all structural degrees of freedom. Therefore, it is of great theoretical and practical significance to study the optimal layout of sensors for civil engineering. The optimal layout of the sensor is to evaluate and monitor the civil engineering structure through a reasonably arranged limited sensor, which is a combinatorial optimization problem. At present, the algorithms for solving this problem are traditional optimization algorithms, sequence methods and intelligent optimization algorithms. Both traditional optimization algorithms and sequence methods can only obtain suboptimal solutions, which cannot guarantee the accuracy of sensor placement. In view of this, this paper proposes a sensor optimization arrangement based on the intelligent algorithm emerging in recent years. This paper introduces several common intelligent optimization algorithms, and proposes a hybrid intelligent algorithm combining Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) algorithm. By comparing and analyzing the convergence of each algorithm, the results show that the hybrid algorithm has certain advantages over the single intelligent algorithm. In this paper, the hybrid intelligent algorithm is used to optimize the arrangement of the sensor. The experimental results show that the optimal layout of the sensor has certain rationality and feasibility.