Behavior Of Specific Heat Research Articles

Thermodynamic properties, electronic and crystallographic structure, and magnetic response of the Sr2HoNbO6 material

En el presente trabajo se utilizó el código Wien2k, en el marco de la teoría del funcional de la densidad de Kohn-Sham, aplicando el método de ondas planas aumentadas y linealizadas (full-potential linearized augmented plane wave, FP- LAPW) y adoptando la aproximación de gradiente generalizado (GGA) de Perdew, Burke y Ernzerhof para la energía de intercambio y correlación, así como la aproximación de densidad local (local density approximation, LDA) para el cálculo de la densidad de estados y la estructura de bandas de la perovskita doble Sr2HoNbO6. Para los cálculos se consideró el grupo Fmm (#225), experimentalmente obtenido a partir de mediciones de difracción de rayos X y del método de refinamiento de Rietveld. El parámetro de red experimental fue de 8.018 Å, el cual concuerda en un 99,2 % con las predicciones teóricas efectuadas a partir de la minimización de la energía mediante la ecuación de estado de Murnaghan. A partir de mediciones de susceptibilidad magnética en función de la temperatura y del ajuste con la ley de Curie, se obtuvo el valor del momento magnético efectivo 10,01 μB. Este valor es muy cercano del esperado teóricamente a partir de las reglas de Hund (10,60 μB). La brecha de energía determinada entre las bandas de valencia y de conducción fue de 3,3 eV, lo que revela el carácter aislante de la perovskita compleja Sr2HoNbO6 para la configuración de espín hacia arriba, en tanto que se observó el carácter semiconductor para la polarización de espín hacia abajo, con una brecha de energía de 0,77 eV. Las propiedades termodinámicas se calcularon a partir de la ecuación de estado usando el modelo cuasi-armónico de Debye. Un comportamiento del calor específico, con CV≈CP, se encontró a temperaturas inferiores a T = 500 K, con valores del límite de Dulong-Petit que doblaban los que se han reportado para materiales del tipo de la perovskita. © 2018. Acad. Colomb. Cienc. Ex. Fis. Nat.

Physical properties of the magnetically frustrated very-heavy-fermion compound YbCu4Ni

The physical properties of the very-heavy-fermion compound ${\mathrm{YbCu}}_{4}\mathrm{Ni}$ were characterized through structural, magnetic, thermal, and transport studies along nearly four decades of temperature ranging between 50 mK and 300 K. At high temperature, the crystal electric field level splitting was determined with ${\mathrm{\ensuremath{\Delta}}}_{1}({\mathrm{\ensuremath{\Gamma}}}_{6})=85\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and ${\mathrm{\ensuremath{\Delta}}}_{2}({\mathrm{\ensuremath{\Gamma}}}_{8})\ensuremath{\approx}200\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, the latter being a quartet in this cubic symmetry. An effective magnetic moment ${\ensuremath{\mu}}_{\mathrm{eff}}\ensuremath{\approx}3{\ensuremath{\mu}}_{B}$ is evaluated for the ${\mathrm{\ensuremath{\Gamma}}}_{7}$ ground state, while at high temperature the value for a ${\mathrm{Yb}}^{3+}$ ion is observed. At low temperature this compound shows the typical behavior of a magnetically frustrated system undergoing a change of regime at a characteristic temperature ${T}^{*}\ensuremath{\approx}200\phantom{\rule{0.16em}{0ex}}\mathrm{mK}$ into of Fermi-liquid-type ``plateau'' of the specific heat: ${C}_{m}{/T|}_{T\ensuremath{\rightarrow}0}$ = const. The change in the temperature dependence of the specific heat coincides with a maximum and a discontinuity in respective inductive and dissipative components of the ac susceptibility. More details about the nature of this ground state are revealed by the specific heat behavior under applied magnetic field.

Searching for Gap Zeros in Sr2RuO4 via Field-Angle-Dependent Specific-Heat Measurement

The gap structure of Sr$_2$RuO$_4$, which is a longstanding candidate for a chiral p-wave superconductor, has been investigated from the perspective of the dependence of its specific heat on magnetic field angles at temperatures as low as 0.06 K ($\sim 0.04T_{\rm c}$). Except near $H_{\rm c2}$, its fourfold specific-heat oscillation under an in-plane rotating magnetic field is unlikely to change its sign down to the lowest temperature of 0.06 K. This feature is qualitatively different from nodal quasiparticle excitations of a quasi-two-dimensional superconductor possessing vertical lines of gap minima. The overall specific-heat behavior of Sr$_2$RuO$_4$ can be explained by Doppler-shifted quasiparticles around horizontal line nodes on the Fermi surface, whose in-plane Fermi velocity is highly anisotropic, along with the occurrence of the Pauli-paramagnetic effect. These findings, in particular, the presence of horizontal line nodes in the gap, call for a reconsideration of the order parameter of Sr$_2$RuO$_4$.

A new application of the liquid thermoelectrics: The detection of magnetic phase transitions

During last years, both solid and liquid thermoelectric materials proved to be useful tools for thermal inspection of condensed matter samples. Used in contact techniques, the liquid thermoelectrics are very suitable in investigating the thermal properties of solids, mainly due to the perfect solid sample-liquid sensor thermal contact. The paper proposes a new application of the liquid thermoelectrics (LTE): the detection of phase transitions. In order to prove the suitability of this application, Cr2O3 single crystal was selected as a sample – Cr2O3 is a well-known antiferromagnetic material involved in a phase transition at a Néel temperature around 34 °C. A LTE material (octanol + 10−2 mol/l tetrabutylammonium nitrate (TBAN)) was used as a sensor for the detection of the antiferro-paramagnetic phase transition of Cr2O3. Based on the recently developed theory of the photothermoelectric (PTE) method, the measured amplitude and phase of the complex PTE signal were converted in thermal parameters. As a consequence, the behavior of the static volume specific heat and dynamic thermal diffusivity, conductivity and effusivity of Cr2O3, around the Néel point, have been obtained. A comparison with similar investigations, obtained by using CuCrO2 (a solid thermoelectric materials) as a sensor, was performed. The results obtained with LTE as a sensor proved to be more accurate, due to the previously mentioned “perfect liquid sensor-solid sample” thermal contact.

Ab Initio Study of the Electronic Structure, Elastic Properties, Magnetic Feature and Thermodynamic Properties of the Ba2NiMoO6 Material

We report first-principles calculations of the elastic properties, electronic structure and magnetic behavior performed over the Ba2NiMoO6 double perovskite. Calculations are carried out through the full-potential linear augmented plane-wave method within the framework of the Density Functional Theory (DFT) with exchange and correlation effects in the Generalized Gradient and Local Density Approximations, including spin polarization. The elastic properties calculated are bulk modulus (B), the elastic constants (C11, C12 and C44), the Zener anisotropy factor (A), the isotropic shear modulus (G), the Young modulus (Y) and the Poisson ratio (υ). Structural parameters, total energies and cohesive properties of the perovskite are studied by means of minimization of internal parameters with the Murnaghan equation, where the structural parameters are in good agreement with experimental data. Furthermore, we have explored different antiferromagnetic configurations in order to describe the magnetic ground state of this compound. The pressure and temperature dependence of specific heat, thermal expansion coefficient, Debye temperature and Gruneisen parameter were calculated by DFT from the state equation using the quasi-harmonic model of Debye. A specific heat behavior CV ≈ CP was found at temperatures below T = 400 K, with Dulong–Petit limit values, which is higher than those, reported for simple perovskites.

Ab-initio analysis of magnetic, structural, electronic and thermodynamic properties of the Ba2TiMnO6 manganite

Los materiales de tipo perovskita que incluyen elementos magnéticos son relevantes debido a sus perspectivas de aplicabilidad tecnológica en la industria de la espintrónica. En este trabajo fueron investigadas las propiedades magnéticas, estructurales, electrónicas y termodinámicas de la manganita de tipo perovskita Ba2TiMnO6. Los cálculos fueron realizados a través del método del potencial de ondas planas aumentadas y linealizadas (FP-LAPW), en el marco de la Teoría del Funcional Densidad (DFT), con efectos de intercambio y correlación en las aproximaciones de gradiente generalizado (GGA) y de densidad local (LDA), incluyendo polarización de espín. A partir de la minimización de la energía en función del volumen, usando la ecuación de estado de Murnaghan se obtuvieron los parámetros de equilibrio de la red las propiedades de cohesión de este compuesto. El estudio de la estructura electrónica se basó en el análisis de la densidad de estados (DOS) y la estructura de bandas, mostrando que este compuesto evidencia un momento magnético efectivo de 3.0 μB. la dependencia con la temperatura y la presión del calor específico, la entropía, el coeficiente de expansión térmica, la temperatura de Debye y el parámetro de Grüneisen fueron calculados mediante DFT a partir de la ecuación de estado, usando el modelo cuasi-armónico de Debye. Se encontró que el calor específico CV≈CP para temperaturas por debajo de T = 400 K, con un límite de Dulong-Petit relativamente mayor que el reportado para perovskitas simples.

Specific heat characteristics of Ce70Ga8.5Cu18.5Ni3 metallic glass at low temperatures

Specific heat behaviors have been studied in Ce70Ga8.5Cu18.5Ni3 bulk metallic glass (BMG) from 2 K to 50 K. The low-temperature specific heat of the Ce-based metallic glass is a combined action of the Fermi liquids term, Debye oscillator term, and Einstein oscillator term as well as excess term. We also observed an intense boson peak around 15 K and attributed it to a harmonic localized Einstein mode influenced by the dense-packed atomic cluster structure. It is also demonstrated that Ce70Ga8.5Cu18.5Ni3 BMG belongs to the strongly correlated heavy-fermion system with a great electron specific heat coefficient and a high Wilson ratio. It exhibits a typical Fermi-Liquid feature when the temperature is above 10 K, while it exhibits a Non-Fermi-Liquid feature when the temperature is below 3.5 K.

Specific Heat Behavior in the Kondo Lattice Model With Hybridization Interaction Under Low Temperature Regimes

A finite size analysis of the Kondo lattice model with hybridization interaction between localized and extended orbitals using the exact diagonalization technique has brought more insight into the specific heat behavior of the heavy fermion (HF) systems under low temperature regimes. The specific heat under the antiferromagnetic region of temperatures below 3k is lower than that of the ferromagnetic region. While the specific heat for temperatures above 4k, shows a reversed trend.

Specific heat study of La1–xCaxMnO3 (0.5 ≤ x ≤ 0.9) with antiferromagnetic ground state

Specific heat data for La1–xCaxMnO3 compounds (1/2 ≤ x ≤ 0.9) are reported. For (1/2 ≤ x ≤ 0.8), the electronic specific heat displays two peaks. The first peak (at high temperatures) is related to the charge/orbital ordering and the second to the spin ordering transition. For x ≥ 0.85, the two peaks merge. Based on the behavior of low temperature specific heat, the low-lying excitations display a drastic change for x > 0.6. For samples with 1/2 ≤ x ≤ 0.6, the low temperature specific heat can be analyzed using a cubic term (C ∼ T3) arising from phonons and antiferromagnetic magnon excitations and an anomalous square term C ∼ T2 of unknown origin. For 0.6 ≤ x ≤ 0.9, the cubic term remains, while the anomalous term disappears. An unexpected linear term is required to fit the low temperature specific heat data. This novel finding is experimental proof that the low-lying CE, 2/3, 3/4, C and G states are different. Using reasonable values for the lattice specific heat, the temperature variation of the electronic entropy has been estimated.

Transformation entropy change and precursor phenomena in Ni-rich Ti–Ni shape memory alloys

Abstract

Effect of Gap Parameter on Electronic Heat Capacity and Magnetic Susceptibility of Graphene in the Presence of Holstein Phonons

Thermodynamic properties of gapped graphene-like structures by considering the effects of interaction between electrons and Holstein phonons have been studied. Particularly, we study the heat capacity and paramagnetic susceptibility of structures as a function of temperature within the Green’s function method with the help of Holstein model. The paramagnetic susceptibility and heat capacity can be derived by using density of states based on the Kubo formula. We have found the energy dependence of density of states for various values of gap in the presence of Holstein phonons. Finally, the temperature behaviors of specific heat and spin susceptibility of gapped graphene structure due to electron-phonon coupling have been investigated. Our results show the electron-phonon interaction leads to the appearance of a double van Hov singularity for each value of gap parameter. Also, electron-phonon coupling affects the value of heat capacity and magnetic susceptibility at low temperatures.

A generalized multifluid optimal pressure for heat exchangers operating with supercritical fluid

ABSTRACTDistinct thermophysical properties encountered in supercritical fluids operating near the critical point have made them strong candidates for working fluids in various engineering applications. Particularly due to the existence of heat capacity maxima near the critical point, heat transfer involving supercritical fluids and their employment in power generation systems have received special attention. In this paper, the existence of optimal operating pressures that maximize the global conductance of supercritical heat exchangers is demonstrated. Analysis of the behavior of the isobaric specific heat along the heat transfer process shows that optimal performance is achieved when the average isobaric specific heat is maximized. Consequently, optimal pressure maps can be created to assist heat exchanger design for various combinations of inlet temperatures and heat transfer rates. Furthermore, it is demonstrated that simple dimensionless groups can correlate—with a mean absolute error (MAE) of 0.0332—the optimal operating pressures of up to 122 different fluids. In addition, it is shown that the correlation is even stronger closer to the critical point and for separate classes of fluids, where MAE can be as low as 0.0103 for triatomic substances.

Multicanonical sampling of the space of states of ℋ(2, n)-vector models

Problems of temperature behavior of specific heat are solved by the entropy simulation method for Ising models on a simple square lattice and a square spin ice (SSI) lattice with nearest neighbor interaction, models of hexagonal lattices with short-range (SR) dipole interaction, as well as with long-range (LR) dipole interaction and free boundary conditions, and models of spin quasilattices with finite interaction radius. It is established that systems of a finite number of Ising spins with LR dipole interaction can have unusual thermodynamic properties characterized by several specific-heat peaks in the absence of an external magnetic field. For a parallel multicanonical sampling method, optimal schemes are found empirically for partitioning the space of states into energy bands for Ising and SSI models, methods of concatenation and renormalization of histograms are discussed, and a flatness criterion of histograms is proposed. It is established that there is no phase transition in a model with nearest neighbor interaction on a hexagonal lattice, while the temperature behavior of specific heat exhibits singularity in the same model, in case of LR interaction. A spin quasilattice is found that exhibits a nonzero value of residual entropy.

Thermal and Dimensional Stability of Injection-Molded Sisal-Glass Fiber Hybrid PP Biocomposites

This article reports on the thermal and dimensional stability of sisal-glass fiber hybrid biocomposites with 30% fiber (wt%) reinforcement in polypropylene (PP) matrix. Hybrid-fiber effect on thermal properties such as specific heat (Cp), melting and crystallization behavior, thermal degradation and dimensional properties such as water absorption and volumetric coefficient of thermal expansion (CTE) was studied. Hybrid biocomposites showed a decrease in specific heat capacity, % crystallinity and thermal degradation at 210 °C (<0.4 wt%). The analysis of heating and cooling rates (5, 10, 15 °C/min) on crystallization kinetics of hybrid biocomposites showed no significant influence of on melting and crystallization enthalpies. Comparison of injection and extrusion process exhibited increased % crystallinity and fiber attrition in hybrid biocomposites after injection molding. Compared to sisal fibers, degradation in glass fiber length was 18.5 and 15% higher after extrusion and injection molding respectively. Difference in derivative thermograms (DTG) peaks after injection and extrusion process were within 2–3% suggesting the uniform distribution of fibers in PP. On the dimensional stability, hybrid biocomposites showed significant improvement (<0.3 wt%) in water absorption and CTE properties at sub-zero (30 to −30 °C) temperature.

Kagome-like chains with anisotropic ferromagnetic and antiferromagnetic interactions

We consider a spin- kagome-like chain with competing ferro- and antiferromagnetic anisotropic exchange interactions. The ground state phase diagram of this model consists of the ferromagnetic and ferrimagnetic phases. We study the ground state and the low-temperature properties on the phase boundary between these phases. The ground state on this phase boundary is macroscopically degenerate and consists of localized magnon states. We calculate the ground state degeneracy and corresponding residual entropy. The spontaneous magnetization has a jump on the phase boundary confirming the first-order type of the phase transition. In the limit of a strong anisotropy, the spectrum of the low-energy excitations has multi-scale structure governing the peculiar features of the specific heat behavior.

Magnetic properties of ferro-ferrimagnetic ternary alloys withAy(BxC1−x)1−yamorphous structures: Effects of concentration, temperature and magnetic field

Abstract Magnetic properties of mixed spin (3/2, 1, 1/2) ferro-ferrimagnetic ternary alloys of the type A y ( B x C 1 − x ) 1 − y are investigated, by means of the Monte Carlo simulation. For this purpose, the influence of concentration, temperature and an external magnetic field on magnetization, magnetic hysteresis loop, magnetic susceptibility and specific heat of ternary alloys with amorphous structures are examined. We found that the compensation temperature exists for some concentrations. Also, it is observed that these ferrimagnetic ternary alloys indicate double hysteresis loop which have been seen theoretically and experimentally in different magnetic alloys. The thermal behavior of magnetization, hysteresis loop and specific heat are also investigated.

Specific-heat exponent and modified hyperscaling in the 4D random-field Ising model

We report a high-precision numerical estimation of the critical exponent α of the specific heat of the random-field Ising model in four dimensions. Our result indicates a diverging specific-heat behavior and is consistent with the estimation coming from the modified hyperscaling relation using our estimate of θ via the anomalous dimensions η and . Our analysis benefited from a high-statistics zero-temperature numerical simulation of the model for two distributions of the random fields, namely a Gaussian and Poissonian distribution, as well as recent advances in finite-size scaling and reweighting methods for disordered systems. An original estimate of the critical slowing down exponent z of the maximum-flow algorithm used is also provided.

Anomalous spin disordered properties of strongly correlated honeycomb compound In3Cu2VO9

We study the ground-state and finite-temperature magnetic properties of an interlayer frustrated J1 − J2 − Jc Heisenberg model on three-dimensional honeycomb lattice by employing the Schwinger boson mean-field theory, focusing on the low-energy physics in In3Cu2VO9. We find that with the increase of interlayer coupling Jc from 0 to 3.6 meV, the interlayer frustrated system transits from an antiferromagnetic (AFM) phase to a state with intralayer AFM order and interlayer disorder. This spin disordered phase explains not only the intralayer phase transition at TN = 38 K, but also the qualitative behaviors of the intermediate-temperature specific heat and magnetic susceptibility of In3Cu2VO9.

Quasinormal modes and thermodynamics of linearly charged BTZ black holes in massive gravity in (anti) de Sitter space-time

In this work we study the Quasi-Normal Modes (QNMs) under massless scalar perturbations and the thermodynamics of linearly charged BTZ black holes in massive gravity in the (Anti)de Sitter ((A)dS) space-time. It is found that the behavior of QNMs changes with the massive parameter of the graviton and also with the charge of the black hole. The thermodynamics of such black holes in the (A)dS space-time is also analyzed in detail. The behavior of specific heat with temperature for such black holes gives an indication of a phase transition that depends on the massive parameter of the graviton and also on the charge of the black hole.

Microcanonical finite-size scaling of an ideal Bose gas in a box

We derive an exact recursive scheme to determine exactly the microcanonical partition function of a finite Bose system. Such a recursive approach is identical to that previously obtained within the context of counting statistics. Within the exact microcanonical ensemble, we study microcanonical finite-size scaling behaviors of condensate fraction and specific heat around the critical energy ϵ c for the finite ideal Bose system. We show that the microcanonical scaling functions governing the various critical behaviors are universal in the ideal Bose-Einstein condensates.