Specific Heats at Low Temperatures

Gopal, E. S. R.

doi:10.1007/978-1-4684-9081-7

Cited by 710 publications

(299 citation statements)

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“…28 In order to reduce the fitting parameters we first determine β from the low-temperature specific heat data of LaIr 2 B 2 . An analysis of the low-temperature C(T ) data of LaIr 2 B 2 by…”

Section: Resultsmentioning

confidence: 99%

Ferromagnetic ordering in CeIr2B2: Transport, magnetization, specific heat, and NMR studies

et al. 2012

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We present a complete characterization of ferromagnetic system CeIr2B2 using powder x-ray diffraction XRD, magnetic susceptibility χ(T ), isothermal magnetization M (H), specific heat C(T ), electrical resistivity ρ(T, H), and thermoelectric power S(T ) measurements. Furthermore 11 B NMR study was performed to probe the magnetism on a microscopic scale. Rietveld refinement of powder XRD data confirms that CeIr2B2 crystrallizes in CaRh2B2-type orthorhombic structure (space group fddd ). The χ(T ), C(T ) and ρ(T) data confirm bulk ferromagnetic ordering with Tc = 5.1 K. Ce ions in CeIr2B2 are in stable trivalent state. Our low-temperature C(T ) data measured down to 0.4 K yield Sommerfeld coefficient γ = 73(4) mJ/mol K 2 which is much smaller than the previously reported value of γ = 180 mJ/mol K 2 deduced from the specific heat measurement down to 2.5 K. For LaIr2B2 γ = 6(1) mJ/mol K 2 which implies the density of states at the Fermi level D(EF ) = 2.54 states/(eV f.u.) for both spin directions. The renormalization factor for quasi-particle density of states and hence for quasi-particle mass due to 4f correlations in CeIr2B2 is ≈ 12. The Kondo temperature TK ∼ 4 K is estimated from the jump in specific heat of CeIr2B2 at Tc. Both C(T ) and ρ(T ) data exhibit gapped-magnon behavior in magnetically ordered state with an energy gap Eg ∼ 3.5 K. The ρ data as a function of magnetic field H indicate a large negative magnetoresistance (MR) which is highest for T = 5 K. While at 5 K the negative MR keeps on increasing up to 10 T, at 2 K an upturn is observed near H = 3.5 T. On the other hand, the thermoelectric power data have small absolute values (S ∼ 7 µV/K) indicating a weak Kondo interaction. A shoulder in S(T ) at about 30 K followed by a minimum at ∼ 10 K is attributed to crystal electric field (CEF) effects and the onset of magnetic ordering. 11 B NMR line broadening provides strong evidence of ferromagnetic correlations below 40 K.

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Section: Resultsmentioning

confidence: 99%

Ferromagnetic ordering in CeIr2B2: Transport, magnetization, specific heat, and NMR studies

et al. 2012

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“…However, thought the success of the model proposed by Einstein, the theoretical description introduced by P. Debye in 1912 10 , constitutes the hallmark in the description of the phononic contribution to the specific heat in solids, see e.g. 11 . Essentially, Debye's model is based on the hypothesis of a continuous isotropic solid.…”

Section: Introductionmentioning

confidence: 99%

“…Here the Debye temperature can be directly obtained via A parameter, whereas the effective mass m * of the charge carriers in a metal can be estimated by means of the Sommerfeld coefficient 11 . The latter can be considered the smoking gun, for instance, when discovering materials with heavy-fermion-like behavior.…”

Section: Introductionmentioning

confidence: 99%

Specific Heat Anomalies in Solids Described by a Multilevel Model

Souza¹,

Paupitz²,

Seridonio³

et al. 2016

Braz J Phys

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Specific heat measurements constitute one of the most powerful experimental methods to probe fundamental excitations in solids. After the proposition of Einstein's model, more than one century ago (Annalen der Physik 22, 180 (1907)), several theoretical models have been proposed to describe experimental results. Here we report on a detailed analysis of the two-peak specific heat anomalies observed in several materials. Employing a simple multilevel model, varying the spacing between the energy levels ∆i = (Ei − E0) and the degeneracy of each energy level gi, we derive the required conditions for the appearance of such anomalies. Our findings indicate that a ratio of ∆2/∆1 ≈ 10 between the energy levels and a high degeneracy of one of the energy levels define the twopeaks regime in the specific heat. Our approach accurately matches recent experimental results. Furthermore, using a mean-field approach we calculate the specific heat of a degenerate Schottky-like system undergoing a ferromagnetic (FM) phase transition. Our results reveal that as the degeneracy is increased the Schottky maximum in the specific heat becomes narrow while the peak associated with the FM transition remains unaffected.

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“…One can detect various types of phase transformations by measuring heat capacity as a function of temperature and under magnetic fields. The determination of transition entropy and enthalpy can give direct information on degrees of ordering of microscopic freedoms existing in molecules and conduction electrons [6]. In this paper, we review thermodynamic investigations on organic charge transfer salts of BEDT-TTF focusing on κ-(BEDT-TTF) 2 X systems.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamic Properties of κ-(BEDT-TTF)2X Salts: Electron Correlations and Superconductivity

Nakazawa

2012

Crystals

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Abstract:Heat capacity measurements of κ-(BEDT-TTF) 2 X (BEDT-TTF: Bis(ethylendithio) tetrathiafulvalene, X: counteranions) which are classified as two-dimensional (2D) dimer-Mott system are reported. At first, we explain structural and electronic features originated from rigid dimerization in donor arrangement in 2D layers. The antiferromagnetic Mott insulating phase located at low-pressure region in the phase diagram shows vanishing γ electronic heat capacity coefficient in the heat capacity, which claims opening of a charge-gap in this insulating state. Then, a systematic change of the γ around the Mott boundary region is reported in relation to the glass freezing of ethylene dynamics. The thermodynamic parameters determined by ∆C p /γT c of 10 K class superconductors, κ-(BEDT-TTF) 2 Cu(NCS) 2 and κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br demonstrate that a rather large gap with a strong coupling character appears around the Fermi-surface. On the other hand, the low temperature heat capacity clearly shows a picture of nodal-gap structure due to an anisotropic pairing. The comparison with lower T c compounds in the κ-type structure is also performed so as to discuss overall features of the κ-type superconductors. The heat capacity measurements of hole-doped systems containing mercury in the counteranions show an anomalous enhancement of γ, which is consistent with the T 1 −1 of NMR experiments etc. The results of heat capacity measurements under high pressures are also reported. OPEN ACCESSCrystals 2012, 2 742

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Specific Heats at Low Temperatures

Cited by 710 publications

References 0 publications

Ferromagnetic ordering in CeIr2B2: Transport, magnetization, specific heat, and NMR studies

Ferromagnetic ordering in CeIr2B2: Transport, magnetization, specific heat, and NMR studies

Specific Heat Anomalies in Solids Described by a Multilevel Model

Thermodynamic Properties of κ-(BEDT-TTF)2X Salts: Electron Correlations and Superconductivity

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