Specific Magnetic Susceptibility Research Articles

Mean-field theory of intermediate valence/heavy fermion systems

Abstract In recent years the class of materials known as intermediate valent, Kondolattice or heavy-fermion systems has aroused much interest. The unusual properties of these materials arise from the behaviour of their 4f-(or 5f-)electrons. The strong electron-electron interactions within the 4f shell cause the f-bands of these rare earth or actinide metal containing species to show very high masses. Thus the densities of states are very high, leading to correspondingly high specific heats and magnetic susceptibilities. A mean field theory is described, based on the Anderson lattice model, in which these properties are straightforwardly explained. Its relationship to the 1/N expansion, and the corrections to mean field, are outlined.

Conversions between SI and CGS units for rock magnetism

Conversion factors between SI and CGS units for magnetic susceptibility and other magnetic quantities are described. The relationship between the volume magnetic susceptibility χSI in SI units and the specific magnetic susceptibility χCGS in CGS units is given by the formula χSI=4πρχCGS, where ρ is the density of rocks. A nomogram for their conversion is shown.

Fermi Liquid Theory on the Basis of the Periodic Anderson Hamiltonian

T-linear term of specific heat and magnetic susceptibility at zero temperature are derived for the heavy electron systems, and relations among these quantities are discussed on the basis of the Fermi liquid theory. Further, a rigorous expression of the T2-term of resistivity at low temperatures is also obtained on the basis of Kubo formula. It is shown that the coefficient of the T2-term arising from the electron interaction is strongly enhanced though it vanishes because of the momentum conservation for a free electron system possessing no crystal lattice.

Ce Heavy fermion systems: The nearly trivalent limit of the mixed valence regime

Specific heat, magnetic susceptibility, and resistivity data is presented which suggests that the heavy fermion phenomenon in Ce systems corresponds to the nearly trivalent limit of the mixed valence behavior. This correspondence holds for both heavy fermion lattices and diluted heavy fermion systems.

A simple method of basic properties description of diluted ferromagnetic alloys (Ising model, [formula omitted

A simple method of basic magnetic properties description of diluted ferromagnetic alloys with S = 1 2 is discussed for the case of Ising approximation. As a result the relations for magnetization curve, internal energy, magnetic contribution to specific heat and magnetic susceptibility have been obtained for arbitrary concentration c of magnetic atoms. As an illustration the corresponding curves, calculated for several values of c, have been also presented.

Heavy fermion behavior in the magnetic to nonmagnetic transition of U(In,Sn) 3

The UX 3 systems with X = Ga, In, Tl, Si, Ge, Sn and Pb are a particularly interesting class of uranium compounds because both their magnetic and electronic properties are drastically influenced by f-spd hybridization. We report resistivity, low temperature specific heat, magnetic susceptibility and high field magnetization results for the U(In 1− x Sn x ) 3 is an enhanced paramagnetic system and UIn 3 orders antiferromagnetically with a Néel temperature, T n, equal to 108 K. Upon dilution of USn 3 by UIn 3, the electronic coefficient of the specific heat, γ, as well as the zero temperature limit of the magnetic susceptibility, χ(0), increase dramatically with γ at T = 1.3 K reaching a value of 520 mJ/mol K 2 for x = 0.6. For x = 0.6, both γ and χ(0) decrease and for x = 0.45 the system magnetically orders. The study of a U system represents the first systematic study of the transition from a paramagnetic state to a heavy fermion state followed by a transition to a long ranged magnetically ordered state. The results for U(In,Sn) 3 will be presented and discussed in terms of relevant theories.

Specific Heat and Magnetic Susceptibility Studies on Bromobis (1,4‐Diazacycloheptane) Copper(II) Perchlorate, [Cu(dach)2Br](C104), at Low Temperatures

AbstractSpecific heat and magnetization investigations are made on polycrystalline [Cu(dach)2Br](Cl04) at low temperatures. For temperatures above 25 K, the dc magnetization shows a Curie‐Weiss behaviour with a Curie constant of 7.92 × 103 e.m.u. K/g and a paramagnetic Curie temperature of −60.8 K. The downturn of 1/X vs. T below 25 K is indicative of ferrimagnetic system. The specific heat between 4 and 8 K can be described by the relation: C = 11.9T3 mJ/mol K with the cubic term leading to a Debye temperature of θD = 194 K. Below 4 K the specific heat rises very rapidly suggesting magnetic ordering. This is substantiated by the presence of a sharp peak at 0.95 K in the ac susceptibility results which can be interpreted as being due to a ferrimagnetic phase transition. Both the magnetization and specific heat investigations indicate the behavior of the system to be ferromagnetic at low temperatures which is interpreted as the result of the canted antiferromagnetism of sublattice moments.

X dependence of the electronic properties of cubic NaxWO3.

Analysis of a variety of experimental data for cubic ${\mathrm{Na}}_{\mathrm{x}}$${\mathrm{WO}}_{3}$ (0.5\ensuremath{\le}x\ensuremath{\le}1) indicates that the electronic structure changes significantly with composition x. The lower--conduction-band width decreases and the band gap increases with increasing x. A simple theoretical model is developed which describes the x dependence of the electronic properties of cubic ${\mathrm{Na}}_{\mathrm{x}}$${\mathrm{WO}}_{3}$. The model provides closed-form analytical expressions for the energy bands, and the total and partial density-of-states functions. Results are obtained for the electronic specific heat, effective mass, magnetic susceptibility, and photoemission energy distribution curves of ${\mathrm{Na}}_{\mathrm{x}}$${\mathrm{WO}}_{3}$. These results are shown to agree with experimental data much better than the results of the rigid-band model.

Electronic properties, superconductivity and stability of the ZrRh alloys

Experimental information on the electronic properties of ordered ZrRh alloys is presented through low temperature specific heat and magnetic susceptibility measurements. In general, a low density of states at the Fermi level is deduced and this is explained by a split band regime consistent with the known DOS calculatios for the type of ordered structures considered. The existence of a split band is considered as typical of stable ordered structures. Zr 2Rh, which is a superconductor with T c = 11.2 K possesses a very high electronic specific heat coefficient. It is suggested that this high λ value is associated with a decrease of stability of the ordered structure and an increased ability to form amorphous alloys when the concentration of Zr increases.

MAGNETIC PROPERTIES OF THE RANDOM MIXTURE OF THE ONE-DIMENSIONAL SYSTEM WITH ANISO-TROPIC HEISENBERG EXCHANGE

In this paper, we extend the method proposed in ref. [1] for the calculation of the partition function of the anisotropic Heisenberg spin system, and calculate the specific heat and magnetic susceptibility for random binary mixture of the one-dimensional system with anisotropic Heisenberg exchange.

Kondo-lattice-mixed-valence resistance scaling in heavy-fermion CeCu6 under pressure.

PHYSICAL REVIE% B Kondo-lattice VOLUME 31, NUMBER — mixed-valence resistance scaling in heavy-fermion JANUARY 1985 CeCu6 under pressure J. D. Thompson and Z. Fisk Los Alamos Rational Laboratory, Los Alamos, Xew Mexico 87545 (Received 14 August 1984) From measurements of the electrical resistance of heavy-fermion CeCu6 subjected to hydrostatic pressures, we infer a continuous pressure-induced transition from Kondo-lattice to more strongly mixed-valence behavior. The resistance is found to scale over an appreciable temperature interval with a pressure-dependent characteristic temperature that reflects this transition. Similarities in the resistive behaviors of CeCu6 and CeA13 are discussed. There now appears to be a distinct class of materials characterized by huge electronic specific heats (y's) and correspondingly large effective electronic masses. ' Each of the known representatives of this class of heavy- fermion materials contain either 4f or 5f elements. Whether the large-y enhancements are a result of the in- trinsic electronic band structure or many-body effects remains an open question. What is clear, however, from thermal variations in properties such as specific heat, magnetic susceptibility, and resistivity is that electronic excitations from the heavy-mass ground state develop on a characteristic temperature scale that is small, typically much lower than phonon energies. Such observations sug- gest that sufficient energy could be supplied by routine high-pressure techniques to perturb noticeably the elec- tronic spectrum of these materials. Recent1y, CeCu6 was discovered to have an electronic specific heat y(T =0) of about 1. 6 J/mole K, making it one of the largest-y materials known. Many of the physi- cal properties of CeCu6 are strikingly similar to those ' of CeA13, which for some time has been considered a proto- typical Kondo-lattice system. Percheron et al. have shown that Kondo-like thermal variations in the electrical resistivity of CeA13 are strongly pressure dependent. Al- though a complete analysis of their data was hampered by irreversibilities in the resistivity large pressure-induced value of CeA13, they were able to conclude that the cerium 4f level moved closer to the Fermi level with applied pres- sure. seen by Percheron The troublesome irreversibility et al. was attributed to pressure-induced formation of an allotropic form of CeA13, with unknown properties. Be- cause of the possibility that CeCu6 might not suffer this complication and consequently represent a cleaner system to study, we have measured the effect of pressure on the electrical resistance of CeCu6. As we will show, in many ways the analogy between CeA13 and CeCu6 persists at high pressures. However, because the resistance of CeCu6 is reversible with pressure, a somewhat different and more straightforward interpretation of the high-pressure prop- erties of CeCu6 is possible. Four-probe ac resistance measurements were made on a single crystal of CeCu6 grown by slow cooling from a melt. The direction of current flow with respect to crys- X-ray analysis tallographic axes was not determined. showed only lines characteristic of the CeCu6 orthorhom- bic structure. The resistance was determined over the 300 K and at hydrostatic pres- temperature interval 1 — sures up to 18 kbar, generated by a self-clamping pressure cell whose operation has been described in detail else- where. resistance We show in Fig. 1 the temperature-dependent of CeCu6 at five fixed clamp pressures. Numbers beside each curve correspond to the order in which pressure was applied. Curve 5 fits smoothly between curves 2 and 3, indicating the absence of pressure hysteresis seen in CeA13. There are several additional qualitative features of these data that should be noted. At P =0, the resistance decreases with decreasing temperature until it reaches a shallow minimum centered around 195 K. Near 15 K, a well-defined resistive peak develops below which the resis- tance falls rapidly. This behavior is similar to that of CeA13 except the resistance of CeA13 shows no minimum below room temperature and the peak for P =0 occurs at 35 K. With increasing pressure, the peak resistance of CeCu6 becomes less prominent and is shifted to higher 0 kbar (1) kbar (2) II r CeCu II ~ ~ 0 g 8. 5 kbar (5) 1 1. 9 kbar (3) I SI ~]:~ I7. 4 'fe m m 0 kbar r kbar (4) 0. 8 -I I I I kbar kbar 0. 4 &. I I / S. S kbar I: gI I I I I I T(K) I S FIG. 1. Resistance clamp logical shows Curve vs temperature for CeCu6 at five different pressures. Numbers in parentheses indicate the chrono- order in which the curves were acquired. The inset resistance. an expanded view of the low-temperature 5 is not shown for clarity only. The American Physical Society

Thermodynamics of a one-dimensional interacting Fermi system with magnetic impurities

The thermodynamics of a model of a one-dimensional metal with an attractive electron-electron and an antiferromagnetic electron-impurity interaction is fotmulated. The impurity contribution to the specific heat and magnetic susceptibility is calculated numerically.

Specific heat and magnetic susceptibility of nearly stoichiometric and homogeneousNb3Al

A15-type Nb/sub 3/Al has been characterized in the recent past as a ''high-T/sub c/, low-..gamma.. superconductor,'' where ..gamma.. is the electronic specific-heat coefficient. We show that this statement should be revised, previous analyses simply reflecting the imperfect metallurgical state. We succeeded in preparing homogeneous, nearly stoichiometric, bulk Nb/sub 3/Al and reinvestigated the specific heat (from 1 to 50 K) and the magnetic susceptibility (19--300 K) in the highly ordered and a slightly disordered condition. The new results show that ordered Nb/sub 3/Al exhibits a high electronic density of states (..gamma.. = 11.4 mJ K/sup -2/ g-at./sup -1/, N(0)approx. =0.91 eV/sup -1/ atom/sup -1/ spin/sup -1/). Information is provided on the moments of the phonon spectrum and those of the electron-phonon spectral function, the thermodynamical critical field, and the energy gap 2..delta..(0). The present experiments further establish only weak exchange enhancement of the susceptibility; spin fluctuations may therefore be safely neglected. Specific-heat data are also reported for the neighboring sigma-phase Nb/sub 2/Al.

Thermodynamics of the classical, easy-plane ferromagnetic chain with in-plane magnetic field

A path-integral evaluation of the thermodynamics for a continuous, easy-plane, classical ferromagnetic Heisenberg chains with in-plane magnetic field is presented. The technique is restricted to low densities of non-linear (soliton) excitations dressed by spin waves. However, important corrections due to strong out-of-plane spin components are explicitly included and lead to incipient divergences in thermodynamic quantities such as specific heat and magnetic susceptibility. It is suggested that these should be looked for experimentally in materials such as CsNiF3.

Spin glass with short-range interaction induced by an electromagnetic field in semiconductors: II. High temperatures domain

The spin-glass state which occurs in semiconductors due to the spin-spin interaction induced by an electromagnetic field is analysed in the high-temperature domain. The Abrikosov-Moukin model has been considered for this analysis, and the specific heat and magnetic susceptibility as function of temperature have been obtained.

Electronic specific heat and magnetic susceptibility of Ti3P-type compounds

A number of Ti3P-type compounds, mainly based on Zr and Nb, were investigated for their low-temperature specific heat and magnetic susceptibility. Results are presented for Nb3X (X=Si, P, As), Zr3X (X=Si, P, Ge, As), and V3P. We found an interesting correlation between the two electronic properties in the Zr3X (X=Si, P, Ge, As) series. A tentative interpretation of this behavior is proposed.

The virial expansion for RKKY spin glasses

The first two non-trivial terms in the virial expansion for the specific heat, magnetic susceptibility and non-linear susceptibility for an RKKY spin glass are evaluated. Use of an interaction, lattice structure and spin appropriate to CuMn gives good agreements with the high-temperature data. In the region of the spin-glass temperature scaling violations are significant for the susceptibilities, but not for the specific heat.

Specific heat and magnetic susceptibility of the Kondo model

The recently obtained diagonalization of the Kondo model is used to formulate the thermodynamics of the model in terms of integral equations. These are solved to yield the specific heat and susceptibility as a function of the temperature for different magnetic fields. The curves are compared to the experimental data.

Effect of interstate interactions on specific heat and magnetic susceptibility in Anderson-localized system

Electron-electron interactions in Anderson-localized states lead to both ferromagnetic (direct exchange) and antiferromagnetic (kinetic-type exchange) interactions among spins of singly occupied states. Specific heat anomaly, in particular its magnetic field dependence, and magnetic susceptibility at low temperatures are calculated by taking into account the coexistence of ferromagnetic and antiferromagnetic interactions among localized spins within a pair model. It is shown that the experimental results on Si:P can be well explained by the present theory.

Low-temperature specific heat, ac susceptibility, and electrical resistivity of amorphous Fe90Zr10, Co90Zr10, and Co86Zr14 alloys

The low-temperature specific heat (CP) and magnetic susceptibility (χ) for the amorphous alloys Fe90Zr10, Co90Zr10, and Co86Zr14 are presented. A very large linear contribution to CP combined with a sharp decrease in χ below about 60 K show Fe90Zr10 to have spin-glass or spin-cluster glass behavior at low temperatures. The Co-based alloys show no deviations from true ferromagnetic behavior at low temperatures. Values of the Debye temperature for all three alloys and the electronic density of states for the Co-based alloys are obtained.