Contribution To Specific Heat Research Articles

Magnetic and electrical transport properties in GdAlSi and SmAlGe

Abstract In this work, we conduct a detailed examination of the magnetic and electrical transport properties in GdAlSi and SmAlGe crystals, which possess a LaPtSi-type structure (space group I41 md). The magnetic susceptibility data unambiguously reveal magnetic ordering below a characteristic transition temperature (T N ). For GdAlSi, a hysteresis loop is observed in the magnetization and magnetoresistance curves within the ab plane when the magnetic field is applied below T N , which is around 32 K. Notable specific heat anomalies are detected at 32 K for GdAlSi and 6 K for SmAlGe, confirming the occurrence of magnetic transitions. Besides, the extracted magnetic entropy at high temperatures is consistent with the theoretical value of Rln(2J+1) for J = 7/2 in Gd3+ and J = 5/2 in Sm3+, respectively. SmAlGe also exhibits Schottky-like specific heat contributions. Additionally, both GdAlSi and SmAlGe exhibit positive magnetoresistance and a normal Hall effect.

Ce2Pd21Si6 vs. Ce3Pd20Si6: Effect of Ce/Pd substitution on the physical properties

In this study, polycrystalline intermetallic compounds Ce3-xPd20+xSi6 (x = 0; 0.5; 1) as well as La-based analogues La3-xPd20+xSi6 (x = 0; 1) are synthesized. At the same time, R2Pd21Si6 (RCe, La) are new rare earth compounds presented here. An analysis of the crystal structure shows that the increase in x leads to partial (x = 0.5) or complete (x = 1) replacement of Ce/La ions by Pd in one of the two Wyckoff positions, namely, in position 4a. Ab initio DFT calculations demonstrate good agreement between the determined lattice parameters and those found experimentally for both Ce3-xPd20+xSi6 (x = 0; 0.5; 1) and La3-xPd20+xSi6 (x = 0; 1). A comparative analysis of resistivity and specific heat of Ce3-xPd20+xSi6 with x = 0; 0.5; 1 makes it possible to associate the Ce ions in the 8c position with Kondo behaviour in all three compositions, which manifests itself in an increase in resistivity with cooling, as well as in a broad peak of the magnetic contribution of specific heat. The Kondo temperature TK ≈ 25 K obtained from the analysis of the temperature dependences of the heat capacity turns out to be the same for all Ce compounds. The appearance of cerium ions in the position 4a in compositions with х = 0 and х = 0.5 leads to an additional contribution to the specific heat, the value of which increases with decreasing temperature, as well as, to the formation of a coherent Kondo-lattice state with a maximum of the resistivity at Tcoh ≈ 15 K, followed by the subsequent onset of negative magnetoresistance regime below Tinv≈ 7 K. Apparently, this behaviour is associated with the appearance of spin and orbital correlations proceeding the quadrupole and antiferromagnetic transitions occurring at lower temperatures. Magnetization measurements show more localized character of magnetic moments of Ce ions at T = 2 K in Ce3Pd20Si6 as compared to the Ce2Pd21Si6.

Study of low-dimensional magnetism in zeolitic imidazolate frameworks

Applying the procedure of a rapid synthesis in the aqueous system, nanocrystalline form of ZIF-8 and Cu-ZIF was obtained. The composition of the latter was inferred from the comparison of vibration spectra and lattice specific heats of both compounds which become nearly identical. The nanocrystalline character of both compounds prevented direct comparison of powder XRD patterns and manifested by the appearance of a boson peak in the diamagnetic ZIF-8 specific heat. The low-temperature magnetic contribution in Cu-ZIF specific heat and a Curie-Weiss tail in low-temperature susceptibility may originate from the effect of surface spins while the round maximum observed in the susceptibility at 135 K indicates the presence of strong low-dimensional correlations with the exchange coupling ∼200 K. Corresponding magnetic contribution cannot be observed in the specific heat due to the huge overlap by the high-temperature lattice contribution. Negligible magnetization values at low temperatures correspond to the aforementioned strong antiferromagnetic coupling. Future experimental scenarios are discussed which should provide better understanding of the bulk and surface magnetism in this unique quantum system.

Specific Heat of Electron Plasma Waves.

Collective modes in a plasma, like phonons in a solid, contribute to a material's equation of state and transport properties, but the long wavelengths of these modes are difficult to simulate with today's finite-size quantum simulation techniques. A simple Debye-type calculation of the specific heat of electron plasma waves is presented, yielding up to 0.05k/e^{-} for warm dense matter (WDM), where thermal and Fermi energies are near 1 Ry=13.6 eV. This overlooked energy reservoir is sufficient to explain reported compression differences between theoretical hydrogen models and shock experiments. Such an additional specific heat contribution refines our understanding of systems passing through the WDM regime, such as the convective threshold in low-mass main-sequence stars, white dwarf envelopes, and substellar objects; WDM x-ray scattering experiments; and the compression of inertial confinement fusion fuels.

Charge density wave and crystalline electric field effects inTmNiC2

Single crystals of ${\mathrm{TmNiC}}_{2}$ were grown by the optical floating-zone technique and were investigated by x-ray diffraction (XRD), thermal expansion, electrical resistivity, specific heat, and magnetic susceptibility measurements. Single-crystal XRD reveals the formation of a commensurate charge density wave (CDW) characterized by a CDW modulation vector ${\mathbf{q}}_{\mathbf{2}\mathbf{c}}=(0.5,0.5,0.5)$, which is accompanied by a symmetry change from the orthorhombic space group $Amm2$ to the monoclinic space group $Cm$, i.e., to a CDW superstructure which is isostructural with that of ${\mathrm{LuNiC}}_{2}$. For all transport and thermodynamic properties, anomalies related to a second order-type thermodynamic CDW phase transition are observed at around ${T}_{\mathrm{CDW}}\ensuremath{\simeq}375\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The large specific heat anomaly at ${T}_{\mathrm{CDW}}, \mathrm{\ensuremath{\Delta}}C\ensuremath{\simeq}6.2\phantom{\rule{4pt}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}{\mathrm{mol}}^{\ensuremath{-}1}{\mathrm{K}}^{\ensuremath{-}1}$, together with noticeable changes in entropy and enthalpy related to the CDW transition, suggests that this point group symmetry breaking CDW phase transition affects more significant parts of the Fermi surface as compared to the incommensurate CDW transition of, e.g., ${\mathrm{SmNiC}}_{2}$ with no change in point group symmetry. The results on the antiferromagnetic and paramagnetic state of ${\mathrm{TmNiC}}_{2}$ obtained by the above macroscopic techniques were complemented by microscopic studies via inelastic neutron scattering. A crystalline electric field modeling of macroscopic susceptibility and magnetic specific heat and entropy contributions as well as microscopic neutron scattering data, reveal crystal field eigenstates and eigenvalues with a ground-state doublet of the Tm-$4f$ electrons, which is well separated by about 25 meV from exited states of the $J=6$ ground-state multiplet.

Universal scaling of specific heat in the S=12 quantum kagome antiferromagnet herbertsmithite

Despite tremendous investigations, a quantum spin liquid (QSL) state realized in a spin-1/2 kagome Heisenberg antiferromagnet remains largely elusive. In herbertsmithite $\mathrm{Zn}{\mathrm{Cu}}_{3}{(\mathrm{O}\mathrm{H})}_{6}{\mathrm{Cl}}_{2}$, a quantum spin liquid candidate on the perfect kagome lattice, precisely characterizing the intrinsic physics of the kagome layers is extremely challenging due to the presence of interlayer Cu/Zn antisite disorder within its crystal structure. Here we measured the specific heat and thermal conductivity of single-crystal herbertsmithite in magnetic fields with high resolution. Strikingly, intrinsic magnetic specific heat contribution arising from the kagome layers exhibits excellent scaling collapse as a function of $T/H$ (temperature/magnetic field). In addition, no residual linear term in the thermal conductivity $\ensuremath{\kappa}/T(T\ensuremath{\rightarrow}0)$ is observed in zero and applied magnetic fields, indicating the absence of itinerant gapless excitations. These results capture a new essential feature of the QSL state of the kagome layers; localized orphan spins are induced by exchange bond randomness, surrounded by a nonitinerant QSL.

Single crystal growth of superconducting UTe2 by molten salt flux method

The molten salt flux method is applied as a synthetic route for the single crystals of the spin-triplet superconductor ${\mathrm{UTe}}_{2}$. The single crystals under an optimized growth condition with excess uranium exhibit a superconducting transition at ${T}_{\mathrm{c}}=2.1\phantom{\rule{4pt}{0ex}}\mathrm{K}$, which is the highest ${T}_{\mathrm{c}}$ reported for this compound. The obtained crystals show a remarkably large residual resistivity ratio with respect to the room temperature value and a small residual electronic contribution in specific heat well below ${T}_{\mathrm{c}}$. These results indicate that the increase of ${T}_{\mathrm{c}}$ in ${\mathrm{UTe}}_{2}$ can be achieved by reducing the disorder associated with uranium vacancies. The excess uranium in the molten salt acts as a reducing agent, preventing tetravalent uranium from becoming pentavalent and suppressing creation of uranium vacancies. At the same time, the relatively low growth temperature can suppress Te volatilization.

Spectroscopic Investigation of Electron-Releasing Functional Groups Substituted N-Iso-Butyl, S-2-Nitro-1-Phenylethyl Dithiocarbamate – A DFT Approach

Quantum chemical calculations have been carried out to explore structural and spectroscopic properties of some derivatives of N-iso-butyl, S-2-nitro-1-phenylethyl dithiocarbamate molecule in neutral and cationic forms. Electron-releasing groups (Me, OH and OMe) are considered to explore their effect on geometrical parameters, vibrational spectra and electronic properties of N-iso-butyl, S-2-nitro-1-phenylethyl dithiocarbamate. All the computations were performed at DFT/B3LYP level of Gaussian09 suite. The Raman spectra at different laser exciting frequencies are presented. The potential energy distributions of the considered derivatives were calculated by using the normal coordinate analysis method. The NBO calculations were performed to study the donor-acceptor interactions, HOMO-LUMO, electronic structure and hyper-conjugative interaction energies. The vibrational contribution of various thermodynamical parameters, viz, entropy, specific heat and free energy have also been presented and discussed in detail. Moreover, we have also explored the effect of temperature at specific heat and partition function of these molecules. Molecular docking studies have been performed to understand the nature of the interactions and the probable binding sites of NSD, NSD-Me, NSD-OH and NSD-OMe molecules in the active pockets of the 2KCE receptor.

The Water Polymorphism and the Liquid–Liquid Transition from Transport Data

NMR spectroscopic literature data are used, in a wide temperature-pressure range (180–350 K and 0.1–400 MPa), to study the water polymorphism and the validity of the liquid–liquid transition (LLT) hypothesis. We have considered the self-diffusion coefficient DS and the reorientational correlation time τθ (obtained from spin-lattice T1 relaxation times), measured, respectively, in bulk and emulsion liquid water from the stable to well inside the metastable supercooled region. As an effect of the hydrogen bond (HB) networking, the isobars of both these transport functions evolve with T by changing by several orders of magnitude, whereas their pressure dependence become more and more pronounced at lower temperatures. Both these transport functions were then studied according to the Adam–Gibbs model, typical of glass forming liquids, obtaining the water configurational entropy and the corresponding specific heat contribution. The comparison of the evaluated CP,conf isobars with the experimentally measured water specific heat reveals the full consistency of this analysis. In particular, the observed CP,conf maxima and its diverging behaviors clearly reveals the presence of the LLT and with a reasonable approximation the liquid–liquid critical point (LLCP) locus in the phase diagram.

Thermo-magnetic characterization of phase transitions in a Ni-Mn-In metamagnetic shape memory alloy

The partially overlapped ferroelastic/martensitic and para-ferromagnetic phase transitions of a Ni50.53Mn33.65In15.82 metamagnetic shape memory alloy have been studied from calorimetric, magnetic and acoustic emission measurement. We have taken advantage of the existence of thermal hysteresis of the first order ferroelastic/martensitic phase transition (~2.5 K) to discriminate the latent heat contribution ΔHt=7.2115 kJkg-1 and the specific heat contribution ΔHc=2161 Jkg-1to the total excess enthalpy of the phase transition. The specific heat was found to follow a step-like behavior at this phase transition. The intermittent dynamics of the ferroelastic/martensitic transition has been characterized as a series of avalaches detected both from acoustic emission and calorimetric measurements. The energy distribution of these avalanche events was found to follow a power law with a characteristic energy exponent ε≅2 which is in agreement with the expected value for a system undergoing a symmetry change from cubic to monoclinic. Finally, the critical behavior of the para-ferromagnetic austenite phase transition that takes place at ~311 K has been studied from the behavior of the specific heat. A critical exponent α≅0.09 has been obtained, which has been shown to be in agreement with previous values reported for Ni-Mn-Ga alloys but different from the critical divergence reported for pure Ni.

Hydrophilic and Hydrophobic Effects on the Structure and Themodynamic Properties of Confined Water: Water in Solutions

NMR spectroscopy is used in the temperature range 180–350 K to study the local order and transport properties of pure liquid water (bulk and confined) and its solutions with glycerol and methanol at different molar fractions. We focused our interest on the hydrophobic effects (HE), i.e., the competition between hydrophilic and hydrophobic interactions. Nowadays, compared to hydrophilicity, little is known about hydrophobicity. Therefore, the main purpose of this study is to gain new information about hydrophobicity. As the liquid water properties are dominated by polymorphism (two coexisting liquid phases of high and low density) due to hydrogen bond interactions (HB), creating (especially in the supercooled regime) the tetrahedral networking, we focused our interest to the HE of these structures. We measured the relaxation times ( and ) and the self-diffusion (D). From these times, we took advantage of the NMR property to follow the behaviors of each molecular component (the hydrophilic and hydrophobic groups) separately. In contrast, D is studied in terms of the Adam–Gibbs model by obtaining the configurational entropy (S) and the specific heat contributions (C). We find that, for the HE, all of the studied quantities behave differently. For water–glycerol, the HB interaction is dominant for all conditions; water–methanol, two different T-regions above and below 265 K are observable, dominated by hydrophobicity and hydrophilicity, respectively. Below this temperature, where the LDL phase and the HB network develops and grows, with the times and C change behaviors leading to maxima and minima. Above it, the HB becomes weak and less stable, the HDL dominates, and hydrophobicity determines the solution.

R3(Fe,T)29 intermetallic compounds - Magnetoelastic coupling in Sm3(CoxFe1-x)29-yCry

The thermal expansion of the rare earth intermetallic compounds Sm3(CoxFe1-x)29-yCry (x = 0.9, y = 7; x = 0.8, y = 6.5; x = 0.7, y = 6) have been systematically investigated by high resolution synchrotron x-ray diffraction measurements (~120–480 K; ~ 300–823 K). The magnetic and thermal properties of Sm3(Fe0.9Co0.1)24Cr4 have been studied as a typical example of the Sm3(CoxFe1-x)29-yCry system by magnetic measurements (ac susceptibility, ~ 5–300 K; DC magnetisation, ~ 77–650 K) and specific heat measurements (~2–300 K). The Debye temperature of Sm3(Co0.9Fe0.1)22Cr7 was found to be θD = 410 ± 10 K from analyses of the specific heat data while the density of states at the Fermi level was N(EF) = 5.08 ± 0. 04 ev−1 atom−1. A pronounced contribution of the nuclear specific heat of Sm3(Co0.9Fe0.1)22Cr7 is evident below 5 K with the nuclear specific heat coefficient found to be A = 758 ± 30 mJ mol−1 K−1. Rietveld analyses of the x-ray diffraction data demonstrate the remarkable magneto-volume anomalies of Sm3(CoxFe1-x)29-yCry around their Curie temperatures TC with negative values of the volume magnetostriction detected below the Curie temperatures and values in the range ωs = − 1.1 × 10−3 to ωs = − 4.3 × 10−3 at 300 K.

High-pressure synthesis of heavily hole-doped cuprates Mg1−xLixCu2O3 with quasi-one-dimensional structure

We investigate electronic properties of hole-doped cuprates ${\mathrm{Mg}}_{1\ensuremath{-}x}{\mathrm{Li}}_{x}{\mathrm{Cu}}_{2}{\mathrm{O}}_{3}$ with the quasi-one-dimensional two-leg-ladder structure. We succeeded in extending the solubility limit of Li in ${\mathrm{Mg}}_{1\ensuremath{-}x}{\mathrm{Li}}_{x}{\mathrm{Cu}}_{2}{\mathrm{O}}_{3}$ from $x=0.12$ to $x=0.60$ by using the high-pressure synthesis technique. The antiferromagnetic transition temperature rapidly decreases with increasing Li content from 94 K at $x=0$ to 7.5 K at $x=0.30$, and takes an almost constant value (3--6 K) at $x\ensuremath{\ge}0.35$. The antiferromagnetic order still exists even at $x=0.60$, where the formal valence of Cu is as large as $+2.30$. The temperature dependence of the specific heat suggests the finite contribution of the electronic specific heat at $x=0.20--0.60$, which is consistent with high valence of Cu. Nevertheless, the temperature dependence of resistivity shows a variable range hopping behavior in the whole $x$ ranges, and the insulating behavior survives under the pressure up to 2.9 GPa. This peculiar behavior is owing to the disorder originating from the intersite atom exchanges due to the similar ionic radius of cations in ${\mathrm{Mg}}_{1\ensuremath{-}x}{\mathrm{Li}}_{x}{\mathrm{Cu}}_{2}{\mathrm{O}}_{3}$. Nonmagnetic ions of ${\mathrm{Mg}}^{2+}$ and ${\mathrm{Li}}^{+}$ are introduced into the ${\mathrm{Cu}}_{2}{\mathrm{O}}_{3}$ planes of ${\mathrm{Mg}}_{1\ensuremath{-}x}{\mathrm{Li}}_{x}{\mathrm{Cu}}_{2}{\mathrm{O}}_{3}$, resulting in the localization of doped hole carriers.

Retrieving CeB6 's lost magnetic entropy

The reported temperature variations of CeB6 s magnetic entropy are inconsistent with the fourfold degeneracy of the crystal field ground state. This old question is here addressed through new specific heat measurements and an improved description, in the cage context, of both the phonons and crystal field contributions to the specific heat. The antiferromagnetic transition is characterized as first-order and its latent heat determined. From the phonons dispersion for a cage compound, the lattice specific heat contribution is derived from the LaB6 data. Once corrected for the first-order transition and lattice contributions, the magnetic entropy displays the characteristic plateau of the quadruplet crystal field ground state, but at temperatures in excess of 30 K. Below 30 K, as the ordering temperature is approached, the magnetic entropy is substantially reduced. This anomalous temperature dependence is consistent with a crystal field ground state split by the rare-earth movement, a phenomenon specific to rare-earth cage compounds.

Gd2Te3: an antiferromagnetic semimetal

We report high-precision magnetization (), magnetic susceptibility (), specific heat (Cp (T, H)) and ‘zero-field’ electrical resistivity, , data taken on Gd2Te3 single crystal over wide ranges of temperature and magnetic field (H), with either -axis or -plane. and unambiguously establish that the b-axis is the easy direction of magnetization whereas any direction in the ac-plane is a hard direction. The -type anomaly in ‘zero-field’ specific heat, Cp (T, H = 0), and an abrupt drop in (characteristic of the paramagnetic (PM) — antiferromagnetic (AFM) phase transition) are observed at the Néel temperature, K. and Cp (T,H) clearly demonstrate that shifts to lower temperatures with increasing H irrespective of whether H points in the easy or hard direction. When , the isotherms at temperatures in the range 2.5 K K reveal the existence of a field-induced spin-flop (SF) transition at fields 4.0 T 4.5 T. The first principles electronic band structure and density of states calculations, based on the density functional theory, correctly predict an AFM ground state (stabilized primarily by the 4f Gd3+ – 5p Te2−– 4f Gd3+ superexchange interactions) and the observed semi-metallic behavior for the Gd2Te3 compound. Moreover, these calculations yield the values for the ordered magnetic moment per Gd atom at T = 0, mJ mol−1 K−2 for the Sommerfeld coefficient for the electronic specific heat contribution and K for the Curie–Weiss temperature, respectively. These theoretical estimates conform well with the corresponding experimental values , mJ mol−1 K−2 and K.

Precisive calculation of specific heat in type-II superconductor under magnetic field

A precisive calculation of specific heat contributions of vortex liquids and solids in type-II superconductor is presented. We use the self-consistent method in the presence of magnetic field for the Ginzburg-Landau description of thermal fluctuations effects in the vortex liquids. Self-consistent calculation of the specific heat summing over all Landau levels is valid for arbitrary values of the magnetic field not too close to Hc1. Our results are in good agreement with the experimental data in a wide region around Tc, including both the vortex liquid below Tc and the normal state above Tc. Our calculation shows that the specific heat behaves as a long tail which persists far into the normal state, indicating the residual superconductivity above Tc.

Highly anisotropic superconducting gaps and possible evidence of antiferromagnetic order in FeSe single crystals

Specific heat has been measured in FeSe single crystals down to 0.414 K under magnetic fields up to 16 T. A sharp specific heat anomaly at about 8.2 K is observed and is related to the superconducting transition. Another jump of specific heat is observed at about 1.08 K which may either reflect an antiferromagnetic transition of the system or a superconducting transition arising from Al impurity. We would argue that this anomaly in low temperature region may be the long sought antiferromagnetic transition in FeSe. Global fitting in wide temperature region shows that the models with a single contribution with isotropic s-wave, anisotropic s-wave, and d-wave gap all do not work well, nor the two isotropic s-wave gaps. We then fit the data by a model with two components in which one has the gap function of $\Delta_0(1+\alpha cos2\theta)$. To have a good global fitting and the entropy conservation for the low temperature transition, we reach a conclusion that the gap minimum should be smaller than 0.15 meV ($\alpha$ = 0.9 to 1), indicating that the superconducting gap(s) are highly anisotropic. Our results are very consistent with the gap structure derived recently from the scanning tunneling spectroscopy measurements and yield specific heat contributions of about 32\% weight from the hole pocket and 68\% from the electron pockets.

New data and developments pertaining to ideas about the electron system of hybridized states of cobalt impurity atoms in a mercury selenide crystal

New experimental data on the manifestation of hybridization and spin polarization effects in 3d-states of donor electrons of a low concentration of cobalt atoms in mercury selenide crystals are obtained. The Hall concentration and mobility of conduction electrons as a function of impurity concentration, and the temperature dependences of the electron mobility, specific heat, and elastic moduli at low temperatures, are investigated. A quantitative interpretation of the observed dependences based on an earlier-developed theory in a justified simplified model of a single localization peak in the electron density of states is performed. As a result, the hybridization parameters of the cobalt states are determined by consistently fitting the observed experimental dependences, and evidence for the spontaneous spin polarization of electrons in the temperature dependences of the impurity specific heat and impurity contribution to the elastic moduli is detected.

Absence of Magnetic Thermal Conductivity in the Quantum Spin-Liquid Candidate YbMgGaO_{4}.

We present the ultralow-temperature specific heat and thermal conductivity measurements on single crystals of YbMgGaO_{4}, which was recently argued to be a promising candidate for a quantum spin liquid (QSL). In a zero magnetic field, a large magnetic contribution of specific heat is observed, and exhibits a power-law temperature dependence (C_{m}∼T^{0.74}). On the contrary, we do not observe any significant contribution of thermal conductivity from magnetic excitations. In magnetic fields H≥6 T, the exponential T dependence of C_{m} and the enhanced thermal conductivity indicate a magnon gap of the fully polarized state. The absence of magnetic thermal conductivity at the zero field in this QSL candidate puts a strong constraint on the theories of its ground state.

A calorimetric investigation of RbFe2As2 single crystals

AbstractWe present properties of single crystals of the iron pnictide superconductor RbFe2As2 grown using a self‐flux method. A bulk superconducting transition at 2.6 K was consistently observed in resistivity, magnetic susceptibility, and specific heat measurements. While the resistivity behaves like a conventional metal at low T, the magnetic susceptibility shows an unusual broad maximum around 80 K in the normal state. A large Sommerfeld coefficient, , was observed seemingly a common feature of heavily hole‐doped “122” compounds. In the superconducting state, we analyzed our specific heat data based on the s‐ and d‐wave two‐gap models. The presence of the small gap with 2/ was discussed to account for the large specific heat contribution remaining to low T far below . The large anisotropy ratio, = / 7 near indicates that the large gap would occupy a highly two‐dimensional Fermi surface.