Magnetic Susceptibility and Specific Heat

In metallic systems, the temperature-independent Pauli susceptibility is a characteristic feature for delocalised carriers [18]. The Pauli susceptibility is directly proportional to the density of states at the Fermi level, i.e. = fPgN(Ep). where p. is the Bohr magneton and N Ep) is the density of states at the Fermi level. Hence, it is possible to determine the N Ep) from the temperature-independent for metallic systems. Usually, in disordered systems, the measured is the sum of both Curie and Pauli terms the Curie term gives an estimate of the localised spins present in the system, and this in turn is a measure of the extent of disorder. 

A small Curie term has been observed in all metallic conducting polymers at very low temperatures (T 20 K) [18]. This indicates the presence of localised spins due to impurities, defects, etc. The x T) of PANI-CSA samples near the M-I transition show this behaviour [50]. The density of states at the Fermi level for metallic PANI-CSA and PPy-PFg samples are one states per eV per two rings and three states per eV per four rings, respectively [51]. These values are rather similar to that obtained from the thermoelectric power measurements. The Curie term at low temperatures is lower for metallic samples than for insulating samples. The magnetic properties and spin dynamics in doped conducting polymers are described in recent review articles [51]. 

Although the resistivity ratio of the insulating PPy-TSO sample is an order of magnitude larger with respect to the metallic PPy-PFg sample, both systems show a linear term in specific heat, and the density of states of the insulating system is only a factor of three lower with respect to that in the metallic sample [51]. Moreover, from the specific heat data [54] it seems that both systems have a finite density of states at the Fermi level, hence the insulating system can be considered as slightly less metallic (less density of states due to localisation) with respect to the real metallic system (i.e., finite conductivity as the temperature tends to 0 K). The comparison of specific heat and conductivity data 

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Based on ac magnetic susceptibility and specific heat measurements, El Massalami et al. (1998a) claimed that they observed superconductivity in CeNi2B2C with Tc of about 0.1 K. If this will be confirmed the mechanisms for superconductivity in the whole borocarbide series should be reconsidered. 

Before the advent of ultraviolet photoelectron spectroscopy and ESCA, experimental evidence on the energy density was mainly available from static magnetic susceptibility and specific heat measurements (134). These provide information on the density of states at the Fermi level and it is impossible to base any conclusions on such experimental information with regard to the shapes of the d-bands in the alloys. It is currently believed that there is very little transfer of d-electrons between the atoms. If an increase in the number of d-electrons on a particular atom does occur, it is due to transfer of electrons from the s,p-band to the lower d-band. This is, of course, related to the difference in electronegativity of the alloying components (135a, 135b). 

Electrical resistivity, Flail constant, magnetic susceptibility and specific heat measurements were performed on the 7 3Au3Sb4 (R = La, Ce, Pr) and the / 3Pt3Sb4 (R = Ce, Pr) com-... 

A rather complete analysis of the magnetic susceptibility and specific heat for Kramers rare-earth ions and Pr in RES has been given by Meijer (1978). In his calculation, Meijer uses the Luttinger-Tisza (1946) approximation and predicts that all the compounds will be antiferromagnetic at low temperatures. 

CeAuln orders antiferromagnetically at 5.7 K as is evident from magnetic susceptibility and specific heat data (Pleger et al., 1987). The electronic specific heat coefficient y is 30 mJ/molK. The temperature dependence of the electrical resistivity of CeAuln shows a magnetic scattering contribution. Thermal conductivity measurements show values of 50 and 60 mW/cmK for LaAuIn and CeAuln, respectively. 

The properties of CesSnj were studied in detail by Lawrence et al. (1991). The resistivity, magnetic susceptibility and specific heat have been measured on a single crystal, which has the tetragonal structure (WsSia type). Moreover a neutron diffraction investigation was carried out on a polycrystalline specimen with the same structure. An antiferromagnetic phase transition was observed at Tn = 17.5 K. The obtained data showed also that CesSny was a moderately heavy fermion compound. At lower temperatures the... 

We have focused on two issues (1) the degree to which the pressure response of the electrical resistivity, magnetic susceptibility and specific heat is similar in a given material or class of materials and how this pressure dependence is related to the Griineisen parameter obtained from ambient pressure measurements and (2) the extent to which this comparison holds in both anomalous lanthanide and actinide compounds. 

SmPtBi Measurements have been made on powder samples of SmPtBi, which is a semimetal (Kim, M.-S. et al., 2001). The electrical resistivity shows a broad maximum of 1.7 mS2cm at 80 K, and the thermoelectric power also reaches a maximum of 60 pV/K at 126 K. The Hall coefficient is positive below 200 K and negative above 200 K. Antiferromagnetic ordering at 2.2 K is manifested by peaks in the dc magnetic susceptibility and specific heat curves. 

YbAlB has the YCrB4-type, Pbam, a = 5.927(2), b = 11.47(1), c = 3.492(1) and golden brown color. With a similar preparation technique (Al flux method to prepare YbB4) Pisk et al. (1981) obtained the compound YbAlB4 with intermediate valence behavior, a = 5.921, b = 11.424, c = 3.507 (structure refinement, YCrB4-type was proposed). Electrical resistivity, magnetic susceptibility and specific heat data were reported. 

The uniform Heisenberg magnetic chain has been an object of study for three quarters of a century, dating back to the initial work of Bethe. Unlike the equivalent Ising and XY-chains, the Heisenberg model cannot be solved analytically. The first calculations of the susceptibility and specific heat... 

Recently, DeLong et al. (1976) reported measurements of the depression of T, the magnetic susceptibility, specific heat and pressure dependence of for (LaSm)Sn3 alloys. The extremely large value of the initial depression of Tc was confirmed by ac susceptibility and specific heat measurements in the superconducting state. 

One the other hand, thermodynamic data are in agreement with the predictions of SIM. There is a consistent relationship between and, say, the peak in the magnetic susceptibility, the specific heat y, and inelastic neutron scattering results. Actually, the only important parameter is in fact Ty from which all other parameters follow within SIM. This has presented a dilemma prior to the emergence of new theories, many of which build on the SIM. Any successful theory must simultaneously be able to correctly predict the microscopic as well as the macroscopic properties. SIM and its extensions appear primarily successftd with the latter. Nevertheless, this fact suggests that at some level NCA is correct. Electron-electron correlations are indeed important, and formation of the singlet state with conduction electrons is not in dispute [except in the model of Liu (1993,1997)]. Somehow this must be reconciled with the existence of bands far above Tk which are suggested by ARPES measurements. 

It is most important to know in this connection the compressibility of the substances concerned, at various temperatures, and in both the liquid and the crystalline state, with its dependent constants such as change of. melting-point with pressure, and effect of pressure upon solubility. Other important data are the existence of new pol3miorphic forms of substances the effect of pressure upon rigidity and its related elastic moduli the effect of pressure upon diathermancy, thermal conductivity, specific heat capacity, and magnetic susceptibility and the effect of pressure in modif dng equilibrium in homogeneous as well as heterogeneous systems. 

We have described in some detail these two properties. Measurements of the magnetic susceptibility and of the electronic specific heat give very clear information, from N(pf), on the presence of an f narrow band. They will be discussed in more detail in Chap. D. 

Figure 6.20 Changes in physical properties of NiS and FeS at the phase transition (a) specific heat (b) resistivity (c) thermoelectric power (d) magnetic susceptibility and (e) lattice parameters. (After Coey et al., 1976.)...

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