Low Temperature Heat Capacity Study Research Articles

Magnetic ordering in Co2+-containing layered double hydroxides via the low-temperature heat capacity and magnetisation study

The low-temperature heat capacity and the magnetisation of Co2+nAl3+ layered double hydroxides (LDH) with the cobalt-to-aluminium ratio n = 2 and 3 and intercalated with different anions have been studied in a wide range of magnetic fields up to 50 kOe. The heat capacity, C(T), was found to demonstrate a Schottky-like anomaly observed as a broad local maximum in the temperature dependence below 10 K. The effect is caused by a splitting of the ground-state Kramers doublet of Co2+ in the internal exchange field and correlates with magnetic ordering in these LDH. In low applied fields, the temperature-dependent dc magnetic susceptibility demonstrates a pronounced rise, which is associated with an onset of magnetic ordering. Both the heat capacity anomaly and the magnetic susceptibility peak are more pronounced for the LDH with n = 2 than for those with n = 3. This feature is associated with an excess of the honeycomb-like CoAl coordination (which corresponds to a 2:1 CoAl ordering) over the statistical cation distribution in Co2Al LDH, while a rather random cobalt-aluminium distribution is typical for Co3Al LDH. The temperature of the Schottky-like anomaly measured in a zero field is independent of the interlayer distance. Application of the magnetic field results in a widening of the anomaly range and a shift to higher temperatures. The observed experimental data are typical for a cluster spin glass ground state.

Low temperature heat capacity study of Co3(BTC)2·12H2O and Ni3(BTC)2·12H2O

Metal-organic coordination compounds have been extensively concerned in recent years due to their attracting chemical and physical properties. However, their thermodynamic properties have not been well investigated compared with the other properties, which would limit understanding their relationship between molecular structure and functional performance from a basic thermodynamic view. In the present work, two crystalline compounds of Co3(BTC)2·12H2O (1) and Ni3(BTC)2·12H2O (2) (BTC = 1,3,5- benzenetricarboxylate) have been designed and synthesized using a solvothermal method. The variable-temperature magnetic susceptibilities of these two compounds have been measured and the results revealed that compounds 1 and 2 possessed antiferromagnetic interaction between CoII/NiII ions. Low temperature heat capacities of these two compounds have been measured using a heat capacity option of Physical Property Measurement System in the temperature range from (1.9 to 300) K, and a Schottky effect has been revealed in the heat capacity curve below 10 K. The experimental heat capacity data have been fitted to a series of theoretical and empirical heat capacity models, and the corresponding thermodynamic functions such as enthalpy and entropy have been calculated in the temperature range from (0–300) K based on these models and fitting parameters. Also, the entire Schottky effect peak has been well presented in the heat capacity curve using these fitted heat capacities. The thermodynamic properties obtained in this work may provide significant thermodynamic basis for further investigating the related functional properties of these two compounds.

Low temperature heat capacity study of Zn, Cd and Mn based coordination compounds synthesized using phenanthroline and halogenated benzoic acid

Four Zn, Cd and Mn based 1,10-phenanthroline and halogenated benzoic acid coordination compounds, formulated as Zn2II(H2O)3(phen)(SO4)·H2O (1, phen = 1,10-phenanthroline), ZnII(phen)(L2)2(H2O) (2, L2 = 2-chloro-4-fluorobenzoic acid), MnIV(phen)(L1)4 (3, L1 = 2-Chloro-4,5-difluorobenzoic acid) and CdII(phen)2(NO3)2 (4), were successfully synthesized and structurally characterized. The low temperature heat capacities of these four compounds were further investigated using a Physical Property Measurement System calorimetric method. The experimental heat capacities were fitted to a series of theoretical and empirical heat capacity models, and the corresponding thermodynamic functions were calculated in the temperature range from (0 to 300) K based on these models and fitting parameters. The low temperature fits indicated that compound 1 can be modeled using only lattice heat capacity contribution, compound 3 modeled using lattice and A-2 term or Schottky heat capacity contributions, and compound 2 and 4 modeled using contributions from lattice, vacancies and one-dimensional phonons with a finite energy onset or gap.

Low temperature heat capacity study of Ba2TiSi2O8 and Sr2TiSi2O8

The heat capacities of powdered Ba2TiSi2O8 and Sr2TiSi2O8 have been measured over the temperature range from (2 to 300)K using a Quantum Design Physical Property Measurement System (PPMS). These two compounds have similar heat capacity values over the experimental temperature range because of their analogous structures. However, the heat capacities do display a crossover at T=112.6K, below which the heat capacity of Ba2TiSi2O8 becomes larger than that of Sr2TiSi2O8. The experimental data have been fitted to a series of theoretical functions from which the thermodynamic functions have been calculated. The standard molar entropies at T=298.15K have been determined to be (254.67±2.55) and (252.61±2.78)J·K−1·mol−1 for Ba2TiSi2O8 and Sr2TiSi2O8, respectively.

Field-induced magnetic ordering and single-ion anisotropy in the quasi-one-dimensional Haldane chain compound SrNi2V2O8: A single-crystal investigation

Field-induced magnetic ordering in the Haldane chain compound SrNi$_{2}$V$_{2}$O$_{8}$ and effect of anisotropy have been investigated using single crystals. Static susceptibility, inelastic neutron scattering, high-field magnetization, and low temperature heat-capacity studies confirm a non-magnetic spin-singlet ground state and a gap between the singlet ground state and triplet excited states. The intra-chain exchange interaction is estimated to be $J \sim 8.9{\pm}$0.1 meV. Splitting of the dispersions into two modes with minimum energies 1.57 and 2.58 meV confirms the existence of single-ion anisotropy $D(S^z){^2}$. The value of {\it D} is estimated to be $-0.51{\pm}0.01$ meV and the easy axis is found to be along the crystallographic {\it c}-axis. Field-induced magnetic ordering has been found with two critical fields [$\mu_0H_c^{\perp c} = 12.0{\pm}$0.2 T and $\mu_0H_c^{\parallel c} = 20.8{\pm}$0.5 T at 4.2 K]. Field-induced three-dimensional magnetic ordering above the critical fields is evident from the heat-capacity, susceptibility, and high-field magnetization study. The Phase diagram in the {\it H-T} plane has been obtained from the high-field magnetization. The observed results are discussed in the light of theoretical predictions as well as earlier experimental reports on Haldane chain compounds.

Low temperature heat capacity study of Fe3PO7 and Fe4(P2O7)3

The low temperature heat capacities of Fe3PO7 and Fe4(P2O7)3 have been measured using a Quantum Design Physical Property Measurement System (PPMS) over the temperature range from (2 to 300)K. Phase transitions due to Fe3+ magnetic ordering have been determined in the heat capacities at temperatures of (164.5 and 47.6)K for Fe3PO7 and Fe4(P2O7)3, respectively, which agrees well with the magnetic measurements reported in the literature. Also, another small transition occurring at around 27K for Fe4(P2O7)3 has been found for the first time. The thermodynamic functions and magnetic heat capacities have been calculated based on the curving fitting of the experimental heat capacity values. Using the fitted heat capacity results, the standard molar entropies have been calculated to be (219.73±2.42)J·K−1·mol−1 and (561.03±6.17)J·K−1·mol−1 for Fe3PO7 and Fe4(P2O7)3, respectively. The calculated magnetic entropy of Fe3PO7 using the magnetic heat capacity suggests that the five 3d-electrons in the Fe3+ are in the t2g orbital with a low spin state according to crystal field theory.

Low temperature heat capacity study of FePO4 and Fe3(P2O7)2

The heat capacities of FePO4 and Fe3(P2O7)2 have been measured using a Quantum Design Physical Property Measurement System (PPMS) over the temperature range from (2 to 300)K. The phase transition due to the Fe3+ magnetic ordering in FePO4 has been determined to occur at T=25.0K, which agrees well with magnetic measurements reported in the literature. For Fe3(P2O7)2, a Schottky anomaly and a four-peak phase transition have been found below 50K. The thermodynamic functions, magnetic heat capacities, and magnetic entropies of these two compounds have been calculated based on curve fitting of the experimental heat capacity values. The standard molar entropy at T=298.15K has been obtained to be (122.21±1.34)J·K−1·mol−1 and (384.12±4.23)J·K−1·mol−1 for FePO4 and Fe3(P2O7)2, respectively.

Low temperature heat capacity Study of Fe(PO3)3 and Fe2P2O7

The heat capacities of two iron phosphates, Fe(PO3)3 and Fe2P2O7, have been measured over the temperature range from (2 to 300) K using the heat capacity option of a Quantum Design Physical Property Measurement System (PPMS). A phase transition related to magnetic ordering has been found in the heat capacity at T=8.76K for Fe(PO3)3 and T=18.96K for Fe2P2O7, which are comparable with literature values from magnetic measurements. By fitting the experimental heat capacity values, the thermodynamic functions, magnetic heat capacities, and magnetic entropies have been determined. Additionally, theoretical fits at low temperatures suggest that Fe2P2O7 has an anisotropic antiferromagnetic contribution to the heat capacity and a large linear term likely caused by oxygen vacancies. Further data fitting in a series over widened temperature regions found that this linear term exists only below 15K and disappears gradually from (15 to 17)K.

Layered LixNiyMnyCo1-2yO2 Cathodes for Lithium Ion Batteries: Understanding Local Structure via Magnetic Properties

The magnetic properties of layered LiNiyMnyCo1-2yO2 (y = 0.5, 0.45, 0.4, and 1/3) compounds are studied in order to understand the transition metal ion distributions via their magnetic interactions. In LiNi0.5Mn0.5O2, an increase of magnetization is found below 100 K with ac magnetic susceptibility revealing broad peaks at 96, 40, 13, and 7 K. The low-temperature neutron diffraction and heat capacity studies do not reveal long-range magnetic ordering; the magnetic component of heat capacity shows a broad peak at 10 K. This behavior is explained by assuming a nonrandom distribution of transition metals. The 96 K transition is attributed to the ordering of clusters of Ni2+ spins in the transition metal and lithium layers, which are coupled by a 180° superexchange mechanism. The wide 40 K peak is explained by an increase of the cluster size due to intralayer Ni and Mn spin ordering, by analogy with antiferromagnetic ordering transitions in Li2MnO3 at 36.5 K and in NaNi0.5Mn0.5O2 at 55 K. The continuing incre...

Low-temperature heat capacity and thermochemical study of [Re 2(Pro) 6(H 2O) 4](ClO 4) 6 (Re = Nd, Gd; Pro = proline) crystals

The heat capacities of two solid complexes of rare-earth compounds with proline [Re 2(Pro) 6(H 2O) 4](ClO 4) 6 (Re=Nd, Gd; Pro=proline, C 5H 9O 2N), were measured with a high-precision automatic adiabatic calorimeter over the temperature range from 78 to 370 K. The heat capacity curves of the two complexes are smooth and similar in magnitude to each other except for a melting transition of [Gd 2(Pro) 6(H 2O) 4](ClO 4) 6 that occurred in the temperature range of 340–346 K with a peak temperature of 342.48±0.01 K. The molar enthalpy and entropy of fusion of [Gd 2(Pro) 6(H 2O) 4](ClO 4) 6 were determined to be 26.104±0.031 k J mol −1 and 76.23±0.08 J K −1 mol −1, respectively, on the basis of the heat capacity measurements. Thermal decompositions of the two complexes were studied through the thermogravimetry (TG) experiments and possible mechanisms of the decompositions were suggested according to the TG analysis. The molar combustion energies of the two complexes were determined to be 17010±1.6 and 15630±1.5 J mol −1 for [Nd 2(Pro) 6(H 2O) 4](ClO 4) 6 and [Gd 2(Pro) 6(H 2O) 4](ClO 4) 6, respectively, by means of oxygen-bomb calorimetric measurements.

Magnetism and superconductivity inM5Rh4Ge10(M=Gd, Tb, Dy, Ho, Er, Tm, Lu, and Y)

Low-temperature resistivity, magnetization and heat-capacity studies are reported for the isostructural M 5 Rh 4 Ge 10 (M=Gd, Tb, Dy, Ho, Er, Tm, Lu, and Y) series. Some of the compounds (M=Gd, Tb, Er, and Tm) show multiple magnetic transitions below 15 K while others (M=Dy and Ho) exhibit only a single magnetic transition. The four magnetic transitions observed for Gd 5 Rh 4 Ge 10 and Tb 5 Rh 4 Ge 10 are unusual in that the one at the highest temperature is a second-order phase transition while the other three are first-order transitions probably involving moment reorientations. An anisotropic exchange interaction is proposed as the cause of the multiple transitions. Of the nonmagnetic compounds, Lu 5 Rh 4 Ge 10 shows superconductivity below 2.4 K whereas Y 5 Rh 4 Ge 10 remains normal down to 1.7 K. The results are compared with those of the previously investigated M 5 Ir 4 Si 10 series.

Heat capacity studies in RPd 2Al 3 (R  Ce, Pr, Nd and Sm) systems

In this paper we report the results of low-temperature (from 1.7 to 40 K) heat-capacity studies in RPd 2Al 3 (R  Ce, Pr, Nd and Sm). Our heat-capacity data on CePd 2Al 3 and SmPd 2Al 3 agree with those of the previous studies. A λ-type anomaly is observed at 6.0 K for NdPd 2Al 3. A large jump (11 J/mol K) in heat-capacity data near the magnetic transition temperature confirms the bulk magnetic ordering in NdPd 2Al 3. The data for PrPd 2Al 3 do not show any magnetic ordering down to 1.7 K. We have calculated the magnetic contribution of entropy due to 4f electrons of all the samples. The temperature dependence of entropy in PrPd 2Al 3 indicates a nonmagnetic singlet ground state. The magnetic contribution to the entropy for all samples at 40 K is less than the corresponding free ion entropy values (R ln(2 J + 1)). This suggests that there is a large crystal-field contribution to the heat-capacity in this series.

Low-temperature heat capacity and thermodynamic properties of four boron nitride modifications

A short review of the low-temperature heat capacity studies of four boron nitride (BN) modifications is presented. C p versus ( T) dependences of high-ordered hexagonal and disordered (turbostratic) modifications were studied by adiabatic calorimetry. The influence of disordering on the heat capacity of boron nitride is shown. The values of thermodynamic properties (heat capacity, entropy, enthalpy, and formation enthalpy) of four BN modifications is reported.

Low-temperature heat-capacity study of the U6X (X=Mn, Fe, Co, Ni) compounds.

Measurements of the superconducting- and normal-state heat capacity of ${\mathrm{U}}_{6}$X (X\ensuremath{\equiv}Mn, Fe, Co, Ni) compounds have been performed over a temperature range 1 K\ensuremath{\lesssim}T\ensuremath{\lesssim}35 K. The ${\mathrm{U}}_{6}$X compounds have strong renormalizations of the free-carrier effective mass ${m}^{\mathrm{*}}$ in the range 10${m}_{e}$\ensuremath{\lesssim}${m}^{\mathrm{*}}$\ensuremath{\lesssim}50${m}_{e}$ (${m}_{e}$\ensuremath{\equiv}free-electron mass). The unusual magnitude and temperature dependence of the ${\mathrm{U}}_{6}$X heat capacities suggest the presence of high densities of low-energy excitations of undetermined nature. The results are analyzed in terms of models appropriate to heavy-fermion liquids, and anisotropic or strong-coupled superconductors. The ${\mathrm{U}}_{6}$X compounds form a link between relatively low-${m}^{\mathrm{*}}$, high-transition-temperature A15 compounds and the more extreme examples of heavy-fermion superconductors such as ${\mathrm{UBe}}_{13}$, ${\mathrm{UPt}}_{3}$, and ${\mathrm{CeCuSi}}_{2}$ for which ${m}^{\mathrm{*}}$\ensuremath{\sim}${10}^{2}$${m}_{e}$. .AE

Low-temperature heat-capacity study of superconducting ternary silicides and germanides with theSc5Co4Si10-type structure

The results of low-temperature specific-heat experiments on eleven superconducting compounds belonging to the ternary system ${R}_{5}$${T}_{4}$${X}_{10}$ (R=Sc, Y, and Lu; T=Co, Rh, Ir, and Os; X=Si and Ge) are presented. Analysis of the data yields relatively high Debye temperatures for the silicides (300--600 K), as well as large values for \ensuremath{\Delta}C/\ensuremath{\gamma}${T}_{c}$ (2.8--4.9) and the electron-phonon interaction \ensuremath{\lambda} (0.60--0.75) for the high-${T}_{c}$ compounds ${\mathrm{Sc}}_{5}$${\mathrm{Rh}}_{4}$${\mathrm{Si}}_{10}$, ${\mathrm{Sc}}_{5}$${\mathrm{Ir}}_{4}$${\mathrm{Si}}_{10}$, and ${\mathrm{Y}}_{5}$${\mathrm{Os}}_{4}$${\mathrm{Ge}}_{10}$, indicating that these are strong-coupled superconductors. The analysis also indicates that a large contribution of the anharmonic term to the total specific heat in the normal state is present in the low-${T}_{c}$ compounds. It is apparent that the phonon spectra of these ${\mathrm{Sc}}_{5}$${\mathrm{Co}}_{4}$${\mathrm{Si}}_{10}$-type materials are quite complex.

Low temperature heat capacity and magnetic study of the quasicrystalline decagonal Al 7 8Mn 2 2 alloy

Low temperature heat capacity and magnetization measurements are reported for the quasicrystalline decagonal (T-phase) alloy Al 7 8Mn 2 2. The heat capacity measurements were performed over the temperature range from 0.5 to 5.0 K and for applied magnetic fields of zero and 12.7 kOe. In this range, the heat capacity is characterized by a broad anomaly near 1 K and no field dependence. The dc magnetization, which was measured from 1.7 to 300 K and with magnetic fields up to 50 kOe, indicates an effective number of one 25.6 μ B localized moment for approximately every 240 Mn atoms. The magnetic susceptibility follows the Curie-Weiss law for T ≧ 15 K, while a spin-glass-like ordering is observed at 7.8 K. Comparisons are made with similar measurements previously reported for the related quasicrystalline icosahedral (I-phase) Al 8 0Mn 2 0 alloy.

Low temperature heat capacity and magnetic study of the Al80Mn20 icosahedral alloy

Abstract Low temperature heat capacity and magnetization measurements are reported for the Al 80 Mn 20 alloy in the quasicrystalline icosahedral phase. The heat capacity, which was measured for temperatures ranging from 0.5 to 5.0 K and magnetic fields up to 11.7 kOe, shows a broad magnetic contribution around 1.0 K. The linear electronic contribution does not indicate an anomalously high density-of-states at the Fermi energy as predicted theoretically for quasicrystalline systems. The d.c. magnetization, which was measured from 2.0 to 300 K and with magnetic fields up to 50 kOe, indicates an effective number of one 11 μ B localized magnetic moment for approximately every 100 Mn atoms. The low field susceptibility follows the Curie-Weiss law for temperatures ≧ 10 K, while a spin-glass-like ordering is observed at low temperatures.

Low temperature heat capacity study of superconducting ternary silicides with the Sc5Co4Si10-type structure

Results of low temperature specific heat experiments on three compounds, Sc 5 Co 4 Si 10, Sc 5 Rh 4 Si 10 and Sc 5 Ir 4 Si 10 which are superconducting with critical temperatures of 4.75, 8.25 and 8.49 K, respectively, are given. Analysis of the data yields relatively large Debye temperatures (400–600 K) plus enhanced electronic density of states and electron-phonon interaction parameters (λ). Based on McMillan's formalism, these compounds are intermediate-coupled superconductors with values of λ ranging from 0.47 to 0.62.

The sodium tungsten bronzes: a study of the changes in electronic structure with composition using high-resolution electron spectroscopy

The variation with composition of the electronic structure of polycrystalline sodium tungsten bronzes NaxWO3(0<x<1) has been studied using a combination of high-resolution electron spectroscopic techniques. Samples on either side of the metal-nonmetal transition (x approximately 0.25 from conductivity data) were used. Low-energy electron energy-loss spectra (LEELS) agree well with those predicted in previous optical studies. In particular the effective electron mass (m*) shows the expected variation with bulk composition. Ultraviolet photoelectron spectroscopy (UPS) has been used to study the valence and conduction bands. Measurements of work function ( phi ); density of states at the Fermi level (g(EF)); and effective electron mass at the Fermi level (mEF*) all show linear variations with bulk composition, in agreement with the findings of magnetic susceptibility and low-temperature specific heat capacity studies. A linear variation of the ratio of the intensities of the conduction and valence bands with bulk composition is also observed across the whole composition range. The variation in shape of the conduction band with composition is consistent with the formation of an impurity band which overlaps a nearly-free-electron-like conduction band that narrows with increasing sodium content. The data obtained in this study are consistent with a mechanism for the metal-nonmetal transition involving the formation of localised small polarons when the electron concentration falls below a critical value.

Low-temperature heat-capacity study of Haucke compounds CaNi5, YNi5, LaNi5, and ThNi5

Low-temperature heat capacities of some Haucke compounds (Ca${\mathrm{Ni}}_{5}$, Y${\mathrm{Ni}}_{5}$, La${\mathrm{Ni}}_{5}$, and Th${\mathrm{Ni}}_{5}$) were studied. The electronic specific-heat constants of these compounds are nearly the same and slightly smaller than that of pure nickel. The Deybe temperatures of these compounds show a wider variation than the electronic specific-heat constants. It is found that the lattice rigidity of these four compounds varies considerably, with that of La${\mathrm{Ni}}_{5}$ being the softest, followed by Ca${\mathrm{Ni}}_{5}$, Th${\mathrm{Ni}}_{5}$, and Y${\mathrm{Ni}}_{5}$ in order of increasing rigidity. This appears to influence their hydrogen absorption capacity. The relative softness is correlated with the Ni-Ni distances in the midplane [$3(g)$ sites], and it is suggested that the Ni atoms in this plane play a critical role in governing the hydrogenation behavior of these materials.