Low-temperature Specific Heat Cp Research Articles

Crystal growth and characterization of CaTe: A potential topological material

High-quality single crystals of CaTe are grown using the high temperature solution-growth method employing Te as the flux. The grown crystals were characterized using single crystal and powder X-ray diffraction, X-ray Laue diffraction, scanning electron microscope and the energy dispersive X-rays analysis for composition mapping. CaTe is an insulator, crystalizing with a cubic NaCl-type of structure. The low-temperature specific heat Cp of CaTe exhibits a peak in Cp/T3 versus temperature T plot near T = 20 K with a conspicuous absence of the Debye T3 regime down to T = 2 K.

Dense Kondo behavior in the low-temperature resistivity and specific heat for amorphous Ce50Al50 alloy

We measured the low-temperature specific heat Cp, resistivity ρ, and magnetoresistance Δρ(H)/ρ(0) for amorphous Ce50Al50 synthesized by a DC high-rate sputter method. The low-temperature Cp (T < 2 K) decreases rapidly toward 0 K and has no indication of phase transition. The value of γ0 which is extrapolated down to 0 K of the Cp/T is 117 mJ/molK2. The temperature dependence of ρ increases with decreasing temperature down to 0.6 K. We found that both a weak localization effect and a coherent Kondo state might be realized in the low-temperature region for the present alloy from the conductivity analysis. Furthermore, in the low-temperature ρ, a T2 term with a very large coefficient A was observed. The ratio of A/γ02 is 0.63 ×10-5 (μΩcm/K2)/(mJ/molK2)2 and is near the value of typical Ce-based heavy-fermion compounds. The magnetoresistances Δρ(H)/ρ(0) at 0.5 K and 2 K are almost constant in the magnetic field region of H < 10 kOe. We considered that the negative magnetoresistance effect is due to the weak localization and the positive magnetoresistance to the heavy-fermion state in the present alloy.

Sizable Residual Quasiparticle Density of States Induced by Impurity Scattering Effect in Ba(Fe1−xCox)2As2 Single Crystals

Low-temperature specific heat Cp is measured on Ba(Fe1–xCox)2As2 single crystals in a wide doping region. A sizeable residual specific heat coefficient γ0 is observed in the low temperature limit of all samples. The specific heat jump near Tc, i.e. ΔCp/T|\\Tc, is also determined. It is found that –γ0, ΔCP/T|\\Tc and Tc all share a similar evolution with doping. These can be well understood within the model of S± pairing symmetry when accounting for the cobalt-dopants as unitary scattering centers in the FeAs planes. Our results reveal a non-trivial impact of impurity scattering in FeAs-based superconductors.

Specific heat of La(Fe0.873Co0.007Al0.12)13 compound in antiferromagnetic and ferromagnetic states

The low-temperature specific heat Cp of La(Fe0.873Co0.007Al0.12)13 compound has been measured in two states: (i) antiferromagnetic (AFM) with a Neel temperature of TN = 192 K and (ii) ferromagnetic (FM). The FM order appears at T = 4.2 K in a sample exposed to an external magnetic field with induction BC ≥ 2.5 T and is retained for a long time in a zero field at temperatures up to T*C = 23 K. The coefficient γFM in the low-temperature specific heat C = γT + βT3 in the FM state differs quite insignificantly from that (γAFM) in the AFM state. Contributions to the low-temperature specific heat, which are related to a change in the elastic and magnetoelastic energy caused by magnetostrictive deformations, are considered.

Percolation limited magnetic order in Eu1-xCaxB6

We report the results of measurements of the low-temperature specific heat Cp(T) and the ac susceptibility χac(T) in low applied magnetic fields for a series of samples of Eu1-xCaxB6. The anomalies in Cp(T), together with the results for χac(T) and M(H), confirm the onset of phase transitions to long range magnetic order for x < 0.7 and provide evidence that for x ≥ 0.7, the Eu moments, which are captured in large magnetic clusters with magnetic moments of the order of 260 μB, adopt a spin-glass type ground state. The data set allows to establish the low-temperature [ T,x] phase diagram of this alloy series.

Low temperature specific heat of a typical glass forming alloy

The Zr41Ti14Cu12.5Ni10Be22.5 alloy in short-range order (SRO) metallic glassy, medium-range order metallic glassy, crystallized, and equilibrium crystalline states was prepared. The low temperature specific heat Cp of the alloy in the different states has been investigated. The results show that the SRO glass has largest specific heat among the four states, and Cp decreases with the extent of crystallization or degree of structural ordering in the alloy. The densities of states at the Fermi level, N(EF), and Debye temperatures, θD, of the alloy are determined. It is found that N(EF) for the SRO glass is highest among the four states, and it decreases with the structural ordering. The phenomenon is interpreted by localization of electrons in glassy alloys. The value of θD increases with degree of structural ordering, indicative of marked soften transverse phonons in the SRO glass compared with the other states.

Low-temperature transport, thermal, and optical properties of single-grain quasicrystals of icosahedral phases in the Y-Mg-Zn and Tb-Mg-Zn alloy systems

We present a comprehensive series of results of electrical transport ~electrical conductivity, magnetoconductivity, Hall effect!, thermal ~specific heat!, and optical ~reflectivity ! measurements in varying temperature ranges between 1.5 and 300 K on high-quality single-grain quasicrystals of icosahedral Y-Mg-Zn. This data set is augmented by the specific-heat and optical-reflectivity data obtained from a single-grain quasicrystal of icosahedral Tb-Mg-Zn. For Y-Mg-Zn, both the electrical conductivity s(T) and magnetoconductivity ds(H) may be described by calculations considering quantum interference effects. A detailed comparison of the weak-localization contributions to s(T) and ds(H) with our experimental data provides estimates of the inelastic and spin-orbit relaxation rates. The inelastic relaxation rate is found to be proportional to T 3 . The dominant contributions to the optical conductivity s 1(v) spectrum, obtained from the reflectivity R(v) data in the frequency range between 16 and 9.7310 4 cm 21 , are a strong Drude feature at low frequencies and a prominent absorption signal centered at approximately 6 310 3 cm 21 . A comparison of the spectral weight of the Drude contribution to s 1(v) with the magnitude of the linear-in-T term gT of the low-temperature specific heat Cp(T) yields the itinerant charge-carrier density ni57.62310 21 cm 23 or 0.13 charge carriers per atom. The low ni value is corroborated by the results of the Hall effect measurements. For Tb-Mg-Zn, the optical conductivity s 1(v) spectrum reveals features similar to those of Y-Mg-Zn. The low-temperature specific heat Cp(T) of Tb-Mg-Zn is strongly influenced by a spin-glass-type freezing of Tb moments and by crystalelectric-field effects.

Low-temperature thermal properties of molecular glasses

We have built up an experimental cell in order to measure low-temperature specific heatC p (T) of molecular glasses and crystals, which are liquid at ambient temperature. We have carried out measurements on ethanol, an organic low-molecular-weight substance, which exhibits at low temperatures three different solid states: a stable crystalline phase, an oricutationally disordered (glassy) crystal, and the true canonical glass,C p (T) measurements of the three phases for both normal and deuterated ethanol from around 2 K up to 30 K are presented. All glasses and disordered crystals show the «anomalous” thermal properties of common glasses.

Low temperature magnetic, thermal, and electrical properties of amorphous (Co100−xMnx)76B24 alloys

The low-field ac magnetic susceptibility (1.5–300 K), low temperature specific heat Cp (0.8–40 K), and electrical resistivity (ρ/ρ300) of the amorphous alloys (Co100−xMnx)76B24 with (0&amp;lt;x&amp;lt;50) have been determined using samples with a common origin. As the magnetic state changes from ferromagnetic to spin-glass the linear contribution to Cp increases by more than a factor of 3. Near the magnetic tricritical point concentration (x≂35) a new sharp discontinuity in the Debye temperature θD(0) is reported. Parallel changes in (ρ/ρ300) occur, and the Debye temperatures obtained from the latter are in excellent agreement with those obtained from CP for the ferromagnetic alloys.

Low temperature thermal properties and intrinsic defects in vitreous silica

Measurements of the low temperature specific heatC p (0.04K≦T≦2.4K) and thermal conductivityk (0.5K≦T≦20K) of high purity vitreous silica (Suprasil W) in the as-received and electron-irradiated states are reported. In the temperature range where the localized excitations inherent in glasses dominateC p (T≲0.5K) no change is observed upon electron irradiation of up to 1019e− (total dose). An anomalyδC around 1.8K is observed inC p which is reduced by 40% upon irradiation. However, ask is not affected by electron irradiation, localized excitations as origin forδC can be ruled out. The density of paramagnetic centers in the most heavily irradiated sample is 5⋅1017cm−3 as obtained from the ESR signal. It has been suggested that these centers have diamagnetic “precursors” in the unirradiated glass. Our measurements indicate that those defects are not associated with the localized excitations.

Specific heat and susceptibility of Ni-based amorphous alloys with dilute Fe

The low temperature specific heat CP and magnetic susceptibility of the amorphous alloys FexNi80−xP14B6 (x=3,5,7) have been determined. For x=3,5 their behavior is consistent with a spin-glass regime, while for x=7 a mictomagnetic regime is observed. The amorphous alloys Ni78P14B8 and Ni80P12B8 show no bulk magnetic order, but CP at low temperatures contains a constant contribution attributed to magnetic clusters, the concentration of which is consistent with previous magnetization measurements.