Temperature Dependence Of Field Research Articles

A dynamical Einstein-Born-Infeld-dilaton model and holographic quarkonium melting in a magnetic field

We generalize the potential reconstruction method to set up a dynamical Einstein-Born-Infeld-dilaton model, which we then use to study holographic quarkonium melting in an external magnetic field. The non-linear nature of the model allows to couple the magnetic field to the quarkonium inner structure without having to introduce back-reacting charged flavour degrees of freedom. The magnetic field dependent melting temperature is computed from the spectral functions and suggests a switch from inverse magnetic to magnetic catalysis when the magnetic field increases. We also discuss the differences due to the anisotropy brought in by the external field.

Study of magnetic field dependent viscosity and temperature on Jenkins model fluid flow over a rotating disk

The present work involves the study of ferrofluid flow over a stretchable rotating disk maintained at an uniform temperature in the presence of magnetic field dependent viscosity. The system is analyzed through the Jenkins model and the simplified governing equations are represented in the cylindrical co-ordinates. The obtained nonlinear coupled partial differential equations are reduced to a coupled nonlinear ordinary differential equations using the well known Von Karman transformation for rotating disk and solved numerically by the shooting method. The velocity profiles, pressure and temperature are studied by varying the stretching parameter, magnetic field dependent viscosity parameter, material constant, and Prandtl number. The comparison for limiting case of the present problem finds good agreement with the existing literature.

Tuning the structural, morphological, optical, dielectric, and magnetic properties of PVA via embedding with CoFe2O4:CuO nanoparticles

Polyvinyl alcohol (PVA) embedded CoFe2O4: CuO (CC) nanocomposites (NC) were prepared by casting technique. The prepared CoFe2O4 (CFO) sample have crystallite size in the range of 20.10–29.08 nm, whereas the crystallite sizes of CuO were found in the range of 20.29–23.68 nm, respectively. TEM images revealed the spherical shape morphology of CC nanocomposite with an average particle size distribution of 15 nm. The Urbach energy of the PCC films increased from 0.44 to 2.590 eV, whereas the direct optical band gaps decreased from 5.584 to 4.345 eV, respectively. The refractive indices of the PCC films were found to be in the range of 1.9–2.6, depending on the different models. Room Temperature-dependent saturation magnetization and coercive field for the prepared nanocomposites were found to be 0.52–1.296 (emu/g) and 1210–1340 (Oe), respectively. The uniaxial magnetic anisotropic constant of PCC films was remarkably enhanced from 0.654x103 to 3.826x103 (erg/cm3) for PCC2, PCC3, and PCC4, correspondingly. The enhanced values of dielectric and magnetic parameters of the prepared nanocomposites suggest their suitability for magnetic recording and memory systems.

Abnormal Magnetic Phase Transition in Mixed-Phase (110)-Oriented FeRh Films on Al2O3 Substrates via the Anomalous Nernst Effect.

Iron rhodium (FeRh) undergoes a first-orderanti-ferromagnetic to ferromagnetic phase transition above its Curie temperature. By measuring the anomalous Nernst effect (ANE) in (110)-oriented FeRh films on Al2O3 substrates, the ANE thermopower over a temperature range of 100-350 K is observed, with similar magnetic transport behaviors observed for in-plane magnetization (IM) and out-of-plane magnetization (PM) configurations. The temperature-dependent magnetization-magnetic field strength (M-H) curves revealed that the ANE voltage is proportional to the magnetization of the material, but additional features magnetic textures not shown in the M-H curves remained intractable. In particular, a sign reversal occurred for the ANE thermopower signal near zero field in the mixed-magnetic-phase films at low temperatures, which is attributed to the diamagnetic properties of the Al2O3 substrate. Finite element method simulations associated with the Heisenberg spin model and Landau-Lifshitz-Gilbert equation strongly supported the abnormal heat transport behavior from the Al2O3 substrate during the experimentally observed magnetic phase transition for the IM and PM configurations. The results demonstrate that FeRh films on an Al2O3 substrate exhibit unusual behavior compared to other ferromagnetic materials, indicating their potential for use in novel applications associated with practical spintronics device design, neuromorphic computing, and magnetic memory.

Temperature dependence of the piezoelectric field in GaInN/GaN quantum wells and its impact on the device performance

Temperature-dependent piezoelectric-field characteristics of GaInN/GaN blue quantum wells are experimentally investigated between 100 and 300 K. The results show that the magnitude of the piezoelectric field increases with decreasing temperature with a slope of 1.08 kV cm−1 K−1 due to the increase in a mismatch between thermal expansion coefficients. To understand the impact of temperature-dependent piezoelectric field on the device performance, the external quantum efficiencies (EQEs) of a blue light-emitting diode are measured in the same temperature range. More severe EQE droops are observed at lower temperatures, which can be attributed to the increase in carrier overflow/spill-over to the p-clad layer enhanced by the stronger piezoelectric fields. The larger blueshifts in mean photon energy are simultaneously observed at lower temperatures, which also confirms the stronger piezoelectric fields at lower temperatures.

Heat Transfer Management of Thermal and Electronics Systems using Convective-Radiative Porous Fins with Thermal Contact Resistance and Diabatic Tip

The miniaturization of electronics, electrical, thermal, mechanical and optical devices and systems calls for increasing demand for efficient cooling systems with higher thermal efficiency. The use of passive mode of cooling using fins has provided unprecedented results. However, the previous transient analyses of the extended surfaces have been done without proper considerations of the imperfect contact between the fin base and the prime surface. Also, the tip of the passive device has been assumed to be adiabatic. However, the present article explores the significances of thermal contact resistance and diabatic tip on the transient thermal response of straight fin with temperature-dependent thermal conductivity and magnetic field under radiative-convective conditions. The nonlinear model is analyzed numerically using generalized Integral Transform Techniques and the numerical results are verified by the exact solution for the linear thermal model. The parametric explorations reveal that the adimensional local temperature in the conductive-radiative fin increases when the conductive-convective, conductive-radiative and magnetic field parameters increase. However, under the assumption of perfect thermal contact between the prime surface and the base of the fin, the adimensional temperature in the fin will decrease as the conductive-convective, conductive-radiative and magnetic field parameters increase. The fin temperature is significantly affected by the Biot numbers under the comparably low values of the conductive-convective, conductive-radiative, magnetic field and thermal conductivity parameters. The effects of the fin thermal conductivity parameter along the fin length depend on the respective values of thermal contact Biot number at the base of the fin and the end cooling Biot number at the tip of the fin. When the thermal conductivity parameter is amplified, the fin adimensional temperature increases when thermal contact Biot number at the base of the fin is zero and the end cooling Biot number at the tip of the fin is very large. This study will help in accurate analysis and design of heat sinks and passive devices for heat transfer enhancement for thermal and electronic systems.

Highly efficient spin-orbit torque generation in bilayer WTe2/Fe3GaTe2 heterostructure

The spin-orbit torque (SOT) phenomenon is crucial for advancing spintronics. Therefore, we explore the SOT efficiency in the WTe2/Fe3GaTe2 heterostructure. The WTe2/Fe3GaTe2 heterostructure has a ferromagnetic ground state with a perpendicular magnetic anisotropy. Through the Metropolis Monte Carlo simulations, we find that the WTe2/Fe3GaTe2 heterostructure has a Curie temperature of 345 K. We also calculate the temperature-dependent coercive field HC(T) via the extended Landau-Lifshitz-Gilbert (LLG) equation, and the estimated coercive field is 0.32 T at 300 K. From the electrical and spin Hall conductivity of the WTe2 layer, we obtain a giant spin Hall angle of ∼4 is obtained at a low chemical potential. Besides, the WTe2/Fe3GaTe2 heterostructure exhibits a critical current density of ∼7.40 × 104 A/cm2 at 300 K. This value is superior to that found in most previously reported materials. Finally, we achieve the switching power consumption of approximately 1.80 × 1015 W/m3 at 300 K, and this is comparable to or even lower than the values found in other bulk type or thick thickness SOT materials. Due to this highly efficient SOT performance, the ultrathin WTe2/Fe3GaTe2 heterostructure may offer a promising avenue for advanced room temperature spintronic applications with implications for both fundamental research and technological advancements.

Thermal scrutinization of a triangular porous fin induced by linear and nonlinear temperature-dependent heat generation and magnetic field effect: the case of Darcy model

Thermal scrutinization of a triangular porous fin induced by linear and nonlinear temperature-dependent heat generation and magnetic field effect: the case of Darcy model

Multilayer ferromagnetic spintronic devices for neuromorphic computing applications.

Based on ferromagnetic thin film systems, spintronic devices show substantial prospects for energy-efficient memory, logic, and unconventional computing paradigms. This paper presents a multilayer ferromagnetic spintronic device's experimental and micromagnetic simulation-based realization for neuromorphic computing applications. The device exhibits a temperature-dependent magnetic field and current-controlled multilevel resistance state switching. To study the scalability of the multilayer spintronic devices for neuromorphic applications, we further simulated the scaled version of the multilayer system read using the magnetic tunnel junction (MTJ) configuration down to 64 nm width. We show the device applications in hardware neural networks using the multiple resistance states as the synaptic weights. A varying pulse amplitude scheme is also proposed to improve the device's weight linearity. The simulated device shows an energy dissipation of 1.23 fJ for a complete potentiation/depression. The neural network based on these devices was trained and tested on the MNIST dataset using a supervised learning algorithm. When integrated as a weight into a 3-layer, fully connected neural network, these devices achieve recognition accuracy above 90% on the MNIST dataset. Thus, the proposed device demonstrates significant potential for neuromorphic computing applications.

Rotational symmetry breaking in superconducting nickelate Nd0.8Sr0.2NiO2 films

The infinite-layer nickelates, isostructural to the high-Tc cuprate superconductors, have emerged as a promising platform to host unconventional superconductivity and stimulated growing interest in the condensed matter community. Despite considerable attention, the superconducting pairing symmetry of the nickelate superconductors, the fundamental characteristic of a superconducting state, is still under debate. Moreover, the strong electronic correlation in the nickelates may give rise to a rich phase diagram, where the underlying interplay between the superconductivity and other emerging quantum states with broken symmetry is awaiting exploration. Here, we study the angular dependence of the transport properties of the infinite-layer nickelate Nd0.8Sr0.2NiO2 superconducting films with Corbino-disk configuration. The azimuthal angular dependence of the magnetoresistance (R(φ)) manifests the rotational symmetry breaking from isotropy to four-fold (C4) anisotropy with increasing magnetic field, revealing a symmetry-breaking phase transition. Approaching the low-temperature and large-magnetic-field regime, an additional two-fold (C2) symmetric component in the R(φ) curves and an anomalous upturn of the temperature-dependent critical field are observed simultaneously, suggesting the emergence of an exotic electronic phase. Our work uncovers the evolution of the quantum states with different rotational symmetries in nickelate superconductors and provides deep insight into their global phase diagram.

Effects of Interfacial Electron Transport on Field Electron Emission from Carbon Nanotube Paste Emitters.

Field electron emission from carbon nanotubes (CNT) is preceded by the transport of electrons from the cathode metal to emission sites. Specifically, a supporting layer indispensable for adhesion of CNT paste emitters onto the cathode metal would impose a potential barrier, depending on its work function and interfacial electron transport behaviors. In this paper, we investigated the supporting layer of silicon carbide and nickel nanoparticles reacted onto a Kovar alloy (Fe-Ni-Co) cathode substrate, which has been adopted for reliable CNT paste emitters. The X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and electrical conductivity measurements showed that the reaction of silicon carbide and nickel nanoparticles on the Kovar metal strongly depends upon the post-vacuum-annealing conditions and can be classified into two procedures of a diffusion-induced reaction (DIR) and a diffusion-limited reaction (DLR). The prolonged annealing at 750 °C for 5 h before the main annealing of the CNT paste emitters at 800 °C for 5 min led to the DIR that has enhanced the Ni silicide phase and a lower potential barrier for the interfacial electron transport, resulting in increased and weakly temperature-dependent field electron emission from the CNT paste emitters. On the other hand, the DLR with only the main anneal of the CNT paste emitters at 800 °C for 5 min gave rise to a higher potential barrier for the electron transport and so lower and strongly temperature-dependent field electron emission. From the results of the interfacial electron transport for the DIR and DLR mechanisms in the CNT paste emitters, we concluded that the ambient temperature dependency of field electron emission from CNT tips in the moderate range of up to 400 °C, still controversial, is mainly attributed to the supporting layer of the CNT emitter rather than its intrinsic electron emission.

Effects of Temperature-Dependent Conductivity and Magnetic Field on the Radiated Carreau Nanofluid Flow and Entropy Generation

This investigation is related to this study of entropy generation during Carreau nanofluid flow under variable thermal conductivity conditions. The heat and mass transfer phenomena are observed in the presence of thermal radiation and activation energy. The flow is induced by a porous stretching surface. Appropriate variables are used in order to simplify the problem into dimensionless form. The numerical simulations are performed by using the shooting technique. The physical aspects of the problem in view of different flow parameters are reported. It is observed that consideration of variable fluid thermal conductivity enhances heat transfer. An enhancement in heat and mass transfer phenomena is observed with increasing the Weissenberg number. Moreover, entropy generation increases with Weissenberg and Brinkman numbers. Current results present applications in thermal processes, heat exchangers, energy systems, combustion and engine design, chemical processes, refrigeration systems, etc.

Molecular Network Approach to Anisotropic Ising Lattices: Parsing Magnetization Dynamics in Er3+ Systems with 0-3-Dimensional Spin Interactivity.

We present a wide-ranging interrogation of the border between single-molecule and solid-state magnetism through a study of erbium-based Ising-type magnetic compounds with a fixed magnetic unit, using three different charge-balancing cations as the means to modulate the crystal packing environment. Properties rooted in the isolated spin Hamiltonian remain fixed, yet careful observation of the dynamics reveals the breakdown of this approximation in a number of interesting ways. First, differences in crystal packing lead to a striking 3 orders of magnitude suppression in magnetic relaxation rates, indicating a rich interplay between intermolecular interactions governed by the anisotropic Ising lattice stabilization and localized slow magnetic relaxation driven by the spin-forbidden nature of quantum tunneling of the f-electron-based magnetization. By means of diverse and rigorous physical methods, including temperature-dependent X-ray crystallography, field, temperature, and time-dependent magnetometry, and the application of a new magnetization fitting technique to quantify the magnetic susceptibility peakshape, we are able to construct a more nuanced view of the role nonzero-dimensional interactions can play in what are predominantly considered zero-dimensional magnetic materials. Specifically, we use low field susceptibility and virgin-curve analysis to isolate metamagnetic spin-flip transitions in each system with a field strength corresponding to the expected strength of the internal dipole-dipole lattice. This behavior is vital to a complete interpretation of the dynamics and is likely common for systems with such high anisotropy. This collective interactivity opens a new realm of possibility for molecular magnetic materials, where their unprecedented localized anisotropy is the determining factor in building higher dimensionality.

Derivative analysis of fractional order on reflection of p-waves with electromagnetic, temperature, and initial stress with three-phase-lag

In this paper, the three-phase-lag model of fractional analysis on the reflection of two-dimensional problem of p-waves with initial stress, temperature-dependent, and magnetic field is investigated. The formulation of the problem for an isotropic homogeneous medium based on a three phase-lag theory. The boundary conditions applied on the surface for the stresses and thermal insulation. The numerical solution presented as well as the graphical representation of the impact of analysis considering the external parameters. Also, the modified elastic waves reflected under the action of the magnetic field, initial stress, fractional degree coefficient, and temperature to determine the more exact nature of the reflection of these waves, particularly seismic waves. A comparison has been made between the results obtained and the previous results obtained by others and already published and are in agreement with these, when external parameters considered in the present investigation neglected. The results obtained indicate that the new external parameters have new impact on the waves reflection and applicable in diverse fields as engineering, earthquakes, volcanos, geophysics, acoustics, and astronomy.

Thermal first-order phase transitions, Ising critical points, and reentrance in the Ising-Heisenberg model on the diamond-decorated square lattice in a magnetic field

The thermal phase transitions of a spin-1/2 Ising-Heisenberg model on the diamond-decorated square lattice in a magnetic field are investigated using a decoration-iteration transformation and classical Monte Carlo simulations. A generalized decoration-iteration transformation maps this model exactly onto an effective classical Ising model on the square lattice with temperature-dependent effective nearest-neighbor interactions and magnetic field strength. The effective field vanishes along a ground-state phase boundary of the original model, separating a ferrimagnetic and a quantum monomer-dimer phase. At finite temperatures this phase boundary gives rise to an exactly solvable surface of discontinuous (first-order) phase transitions, which terminates in a line of Ising critical points. The existence of discontinuous reentrant phase transitions within a narrow parameter regime is reported and explained in terms of the low-energy excitations from both phases. These exact results, obtained from the mapping to the zero-field effective Ising model are corroborated by classical Monte Carlo simulations of the effective model.

Electric-Field Emission Mechanism in Q-Carbon Field Emitters.

In this paper, we report the excellent field emission properties of Q-carbon and analyze its field emission characteristics through structural, morphological, and electronic property correlations, supported by density functional theory (DFT) simulation studies. The Q-carbon field emitters show impressive and stable field emission properties, such as a low turn-on electric field of ∼2.38 V/μm, a high emission current density of ∼33 μA/cm2, and a critical field of ∼2.44 V/μm for the transition from a linear region to the saturation region in the F-N plot. The outstanding field emission properties of Q-carbon are attributed to (i) a unique sp2/sp3 mixture in Q-carbon, (ii) sp2-bonded highly conductive amorphous carbon-rich channels inside the Q-carbon cluster, (iii) a large local field enhancement due to the local geometry and microstructure of Q-carbon, and (iv) the presence of sp2-bonded amorphous carbon regions in the composite film. The temperature-dependent field emission properties, such as extreme sensitivity and an enhancement in the emission current density with temperature, can be explained by the local density of states near the Fermi level and the excellent thermal stability of the Q-carbon field emitters. From DFT simulation studies, the computed work function and the field-enhancement factor were determined to be 3.62 eV and ∼2300, respectively, which explains the excellent field emission characteristics of Q-carbon. The obtained field emission properties, in most cases, were superior to those from other carbon/diamond-based field emitters, which will open new frontiers in field emission-based electronic applications.

Stress-based topology optimization of thermoelastic structures considering self-support constraints

A thermoelastic topology optimization method considering stress and manufacturing constraints is developed for engineering structures under thermo-mechanical coupled field in this paper. A design dependent non-uniform temperature field is considered for the heat conduction and the thermoelastic analysis during the topology optimization. Based on the solid isotropic material with penalization (SIMP), a topology optimization model is formulated to minimize the structural compliance under stress and overhang angle constraints. The overhang angle constraint to achieve the self-support property in additive manufacturing is established by connecting the elemental density values between the printing element and the corresponding support elements in the lower layer. The stress aggregation function is built to approximate the maximum stress value and an improved adaptive normalization scheme is applied to deal with the highly nonlinearity of the optimization. The sensitivity of the objective function and constraints with respect to the design variables are derived by the adjoint method, and the design variables are updated by the gradient-based optimization method. Moreover, a robustness scheme is proposed for the thermoelastic topology optimization to eliminate possible manufacturing issues such as “single node connection” and “thin rod” phenomena. Several typical numerical examples are provided to demonstrate the effectiveness of the proposed method in stress value reduction and overhang angle control. Meanwhile, the topology optimization with robustness scheme is also proved to result in more robust designs for manufacturing.

Compressive and tensile strain effects on the ultrafast carrier dynamics and transport of gallium arsenide thin films on silicon and magnesium oxide substrates

We investigate strain effects on the ultrafast carrier dynamics and transport of gallium arsenide films on silicon (GaAs/Si) and magnesium oxide (GaAs/MgO) substrates using temperature-dependent photoluminescence (PL) and terahertz time-domain spectroscopy (THz-TDS) from 11 K - 300 K. The PL shows that GaAs/Si and GaAs/MgO samples are under tensile and compressive strain at low temperature, respectively. The temperature-dependent THz emission from GaAs/Si does not show significant differences with the emission from bulk GaAs, while the THz emission from GaAs/MgO shows an order-of-magnitude decrease at low temperature. The THz emission from the samples exhibits an interplay between strain-induced effective mass changes and temperature-dependent electric field effects.

Temperature-Independent Coercivity in Compositionally Graded Ferromagnetic Multilayers

We devise nanoscale-designed ferromagnetic thin films with graded exchange-coupling (J) profiles that allow us to obtain constant coercivities over a very extended temperature range. The magnetic structure designed here is composed of two ferromagnetic layers, which are separated by a spacer layer with a linear exchange-graded profile. Our detailed magnetometry analysis on single-crystal $\mathrm{Co}\text{\ensuremath{-}}\mathrm{Ru}$ alloy thin films reveals a coercivity plateau with a relative change of less than 2% over a temperature range of 75 K, whereas conventional films exhibit changes larger than 20%. This remarkable behavior is achieved by means of a strongly temperature-dependent exchange bias between adjacent ferromagnetic portions of our film structures, which are designed to fully compensate for the conventional temperature dependence of the coercive field. This strongly temperature-dependent bias field is mediated by a paramagnetic interlayer in our film design and can be adjusted by a suitable choice of both the spacer-layer composition profile and thickness. Our particular design can be applied to a large variety of magnetic materials and adapted to relevant temperature ranges that are needed to maintain stable coercive field values over a wide operation range in real applications.

Effect of the operation temperature on the hydrodynamics and performances of a cyclone separator

• Effects of temperature on cyclone performances are studied by CFD. • The separation efficiency decreases and quality improves at higher temperatures. • A large drag force to centrifugal force ratio is needed for escape: larger than 10 4 . • The flow field determines submicron particle separation if the ratio is 10 1 to 10 3 . • Locus of zero vertical velocity and turbulence intensity relate to particle capture. The effect of the operation temperature on the cyclone hydrodynamics and performances is numerically investigated by Computational Fluid Dynamics (CFD). When increasing the temperature, the separation efficiency decreases and the separation quality improves due to the weakened double layer swirling flow structure. The radial drag and centrifugal forces exerted on 0.1 μm and 1 μm particles are recorded. A large radial drag force to centrifugal force ratio is required for escape: a ratio larger than 10 4 . When the radial drag force to centrifugal force ratio is in the range of 10 1 to 10 3 , it is the temperature-dependent flow field which determines the submicron particle separation. While the locus of gas zero vertical velocity is closely related to the particle’s separation, the gas turbulence intensity distribution also contributes the capture of the particles.