Magnetic and thermal properties of PrNi2

The results of specific heat and susceptibility measurements on PrNi₂ over the temperature region from 12 mK to 80 K are reported. Anomalies in the susceptibility and the magnetic relaxation time are found at 0.25 K. The specific heat starts to increase around 0.5 K, much higher than 0.25 K, and it continues increasing at the lowest measured temperature of 30 mK. The entropy estimation shows that the specific heat anomaly below 1 K is predominantly nuclear in origin. Data are discussed in terms of a mixed nuclear-electronic transition at 0.25 K.     

Monte Carlo Study of Long-Range Interactions of a Ferroelectric Bilayer with Antiferroelectric Interfacial Coupling

By the use of Monte Carlo simulation, we have studied the critical behavior of a ferroelectric bilayer with antiferroelectric interfacial coupling using the transverse spin- $\frac{1}{2}$ Ising model. We discuss the effects of long-range interactions for the internal energy, specific heat, free energy, dielectric susceptibility, and polarization. The dependence of the Curie temperature on the thickness of the bilayer, long-range interactions, and the transverse field was also investigated. It is assumed that the long-range interaction decays with the distance between the pseudo-spins as a power law.     

Surface magnetism in 3He: Thermodynamics

A phenomenological formulation of the enhancement of the susceptibility of liquid ³He in contact with a dielectric surface is presented. The effective Hamiltonian includes a surface term consisting of both the quadratic and the quartic dependence on the surface order parameter. The partition function for this system is calculated using a novel application of the transfer matrix methods. We find a susceptibility that contains the Curie-Weiss-like surface contribution as well as the appropriate field dependence in agreement with experiments. In addition, we find a weak temperature-dependent anomaly in specific heat as well.Nordita Visiting Professor.     

Influence of the Competition Between Dipolar and Exchange Interactions on the Magnetic Structure of Single-Wall Nanocylinders. Monte Carlo Simulation

In this work, we address the Metropolis Monte Carlo simulation of single-wall magnetic nanocylinders with zig-zag edges on the basis of a three-dimensional classical Heisenberg model with short-range nearest neighbors ferromagnetic exchange interactions and long-range dipolar interactions. A study of the magnetic properties (thermal dependence of the magnetization per site, specific heat, and magnetic susceptibility) with different strengths of dipolar interaction relative to the exchange energy is carried out. Our results reveal a strong dependence of the low-temperature magnetic structure of the nanotubes with the strength (??) of the dipolar interaction. Comparisons with the case without considering dipolar interaction are carried out and a summary of our results in terms of the ??-dependence of the low-temperature magnetization is also presented and discussed.     

Role of Interlayer and Intersite Interactions in Superconducting State in High-Tc Layered Cuprates

We studied the role of interlayer and intersite interactions on transition temperature and specific heat of layered high-T _c cuprates. We used double-time Green's function technique in the spirit of mean field approximation in order to obtain the expressions for hole density, transition temperature, and specific heat. These expressions are found to be dependent on the carrier concentration and intersite and interlayer interactions. The numerical analysis shows that the effect of intersite interaction on transition temperature and specific heat is qualitatively similar to that of interlayer interactions and provides favorable conditions to establish long-range order in the superconducting state.     

Effect of Gap Parameter on Electronic Heat Capacity and Magnetic Susceptibility of Graphene in the Presence of Holstein Phonons

Thermodynamic properties of gapped graphene-like structures by considering the effects of interaction between electrons and Holstein phonons have been studied. Particularly, we study the heat capacity and paramagnetic susceptibility of structures as a function of temperature within the Green’s function method with the help of Holstein model. The paramagnetic susceptibility and heat capacity can be derived by using density of states based on the Kubo formula. We have found the energy dependence of density of states for various values of gap in the presence of Holstein phonons. Finally, the temperature behaviors of specific heat and spin susceptibility of gapped graphene structure due to electron-phonon coupling have been investigated. Our results show the electron-phonon interaction leads to the appearance of a double van Hov singularity for each value of gap parameter. Also, electron-phonon coupling affects the value of heat capacity and magnetic susceptibility at low temperatures.     

Effect of Interlayer Interaction on the Specific Heat of High-Tc Superconductors

The effect of interlayer interactions on the electronic specific heat of high-T _c layered superconductors has been studied within the framework of the Hirsch model. In the present paper we extend our previous work in order to evaluate the expression for specific heat. It is shown that the inclusion of interlayer interactions suppresses the height of the jump in the specific heat at T _c.     

Role of Interlayer and Intersite Interactions in Superconducting State in High-T<Emphasis Type="Italic">c</Emphasis> Layered Cuprates

We studied the role of interlayer and intersite interactions on transition temperature and specific heat of layered high-T _c cuprates. We used double-time Green's function technique in the spirit of mean field approximation in order to obtain the expressions for hole density, transition temperature, and specific heat. These expressions are found to be dependent on the carrier concentration and intersite and interlayer interactions. The numerical analysis shows that the effect of intersite interaction on transition temperature and specific heat is qualitatively similar to that of interlayer interactions and provides favorable conditions to establish long-range order in the superconducting state.     

Effect of Interlayer Interaction on the Specific Heat of High-T c Superconductors

The effect of interlayer interactions on the electronic specific heat of high-T _c layered superconductors has been studied within the framework of the Hirsch model. In the present paper we extend our previous work in order to evaluate the expression for specific heat. It is shown that the inclusion of interlayer interactions suppresses the height of the jump in the specific heat at T _c.     

Spatial dynamics and genetics of infectious diseases on heterogeneous landscapes.

Explicit spatial analysis of infectious disease processes recognizes that host-pathogen interactions occur in specific locations at specific times and that often the nature, direction, intensity and outcome of these interactions depend upon the particular location and identity of both host and pathogen. Spatial context and geographical landscape contribute to the probability of initial disease establishment, direction and velocity of disease spread, the genetic organization of resistance and susceptibility, and the design of appropriate control and management strategies. In this paper, we review the manner in which the physical organization of the landscape has been shown to influence the population dynamics and spatial genetic structure of host-pathogen interactions, and how we might incorporate landscape architecture into spatially explicit population models of the infectious disease process to increase our ability to predict patterns of disease occurrence and optimally design vaccination and control policies.     

Physical properties of iron-sulfur Fe6S6 superclusters important for biological systems

The theoretical analysis of the thermal and magnetic properties of iron-sulfur superclusters has been studied by taking into account Heisenberg interactions and resonance delocalizations (double exchange interactions). The numerical calculations are based on the determination of the lowest energy states for different values of spins (from S = 0.5 to S = 12.5) and Heisenberg exchange integrals. It is shown that the spin magnetic susceptibility of the iron-sulfur superclusters decreases with increasing temperature and increases with increasing the double exchange parameter. In contrast to the susceptibility, the heat capacity decreases with the increasing values of the double exchange parameter. It was theoretically found that spin of ground state for the iron-sulfur supercluster is equal to 0.5. Based on our results, we can state that the Heisenberg model of spin interactions describes the thermodynamic properties of the iron-sulfur superclusters which are the important constituents of proteins and enzymes.     

Magnetic Properties of Ru-rich Ru2?x Fe x CrZ (Z=Si, Ge)

The properties of Heusler compounds Ru_2?x Fe _x CrGe are investigated and compared with those of Ru_1.9Fe_0.1CrSi. Ru₂CrGe is confirmed to exhibit an antiferromagnetic transition with Ne??l temperature 13?K by magnetic susceptibility and specific heat measurements. When Fe is substituted for Ru, a peak in the magnetic susceptibility is observed, and in the lower temperature region irreversibility between temperature dependences of magnetization for zero-field-cooling and field-cooling conditions is found. Nevertheless, in specific heat of Ru_1.9Fe_0.1CrGe, there is no anomaly to indicate phase transition. The specific heat is almost identical to that for Ru_1.9Fe_0.1CrSi. The above results demonstrate that the magnetic states in the low temperature region of Fe-substituted samples are spin-glass-like states. Slight substitution of Fe for Ru destroys the long-range-order and lead to peculiar spin-glass-like states.     

Heat Capacity and Susceptibility of Rare Earth Magnetic Superconductors

Journal of Superconductivity and Novel Magnetism - We calculate the specific heat and susceptibility of rare earth magnetic superconductors in the context of the Ginzburg–Landau theory. The...     

A Shiba-Rusinov theory for paramagnetic impurities in proximity effect sandwiches

The Shiba-Rusinov theory, which takes into account both the potential and exchange interactions existing between a conduction electron and a paramagnetic impurity atom, is used to study the effects due to paramagnetic impurities dissolved in the normal layer of a proximity effect sandwich. Using aT-matrix approach to treat the interactions due to the impurities and the standard Born approximation to treat the other interactions in the sandwich, we obtain a set of self-consistent equations for the renormalized frequencies and the unrenormalized energy gaps for the electrons in both layers. The solutions of these equations are then used to obtain expressions for the decrease in the transition temperature of the sandwich and for the jump in the specific heat atT _c .     

Experimental determination of the thermodynamic properties of three nematic liquid crystals

The results of measurements of the density, the magnetic susceptibility, the molar specific heat, and the heat of the nematic-isotropic transition are reported.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 49, No. 3, pp. 467–472, September, 1985.     

Effect of Disorder Induced by Heavy-Ion Irradiation on CeCoIn5 Superconductivity

We present a study of the effect of heavy-ion irradiation on a thinned single crystal of the unconventional heavy fermion superconductor CeCoIn₅. Magnetic susceptibility and low-temperature specific heat results show that the superconducting transition temperature (T _c) changed only 4% with irradiation of 1×10¹² ions/cm², Energy=1 GeV, while the specific heat jump at T _c, ΔC, divided by C _n, where C _n is the normal state specific heat just above T _c, was reduced to 3.6 from ΔC/C _n=4.5 for unirradiated CeCoIn₅. The increase of low-temperature magnetic susceptibility and the saturation in magnetization suggest that the defects induced by heavy-ion irradiation are magnetic in nature, as was seen in the case of neutron irradiation on the heavy fermion superconductors, UBe₁₃ and UPt₃. The non-Fermi liquid behavior of the irradiated sample, based on the temperature dependence of the low temperature magnetic susceptibility, is significantly altered.     

Quasiparticle interactions and the Bose-Einstein phase transition

We look at a strongly interacting Bose gas in an attempt to understand the effects upon the physics of the phase transition of the interactions between the higher momentum excitations. At densities an order of magnitude below liquid helium, we find that these interactions are affecting the phase transition in a manner reminiscent of the effects of roton-roton interactions upon the lambda transition. We find singularities in the specific heat and infinite slope at the transition temperature for the superfluid density.     

Low-temperature magnetic properties of HoRh4B4

The low-temperature magnetic properties of HoRh₄B₄ have been studied by means of measurements of the magnetic susceptibility, magnetization, specific heat, thermal expansion, and magnetostriction. The ferromagnetic phase transition at T _M= 6.7 K shows almost ideal S = 1/2 mean field behavior in the specific heat. Crystal field effects due to the splitting of the J = 8 Hund's rule ground state of the Ho³⁺ ions result in Schottky anomalies in the specific heat and the thermal expansion and are also revealed in the low-field magnetic susceptibility and the magnetostriction. Information on the ground state doublet of the 4f electrons has been obtained from the nuclear contribution to the specific heat below 1 K and the high-field magnetization below T_M.This research was supported by the Schweizerische Nationalfonds zur Forderung der wissenschaftlichen Forschung (HRO), by the Department of Energy under Contract No. EY-76-S-03-0034-PA227-3 (LDW, MBM), and by the National Science Foundation under Grant No. NSF/DMR77-08469 (DCJ)     

Nuclear cooling in PrCu6

Nuclear adiabatic demagnetization experiments have been performed in the Van Vleck paramagnet PrCu₆ in order to determine the very-low-temperature nuclear magnetic properties of this material and to test its efficiency as a very low-temperature refrigerator. It is found that a temperature of 2.7 mK can be reached from an initial temperature of 40 mK and an initial field of 20 kOe. Susceptibility and specific heat measurements above 2.7 mK indicate the presence of both nuclear quadrupole and exchange interactions. The transition to an antiferromagnetically ordered state among the Pr nuclei is expected to occur below 2.7mK.     

Hydrogen induced stress cracking in supermartensitic stainless steels – Stress threshold for coarse grained HAZ

The objective of the present work was to investigate the influence of the microstructure on the hydrogen cracking susceptibility of two typical pipeline supermartensitic stainless steels. The work has concentrated on the coarse-grained heat affected zone because this is the typical crack initiation point. The hydrogen cracking susceptibility was tested by notched tensile test samples containing a simulated coarse grained heat affected zone. The samples were tested under constant load immersed in 3.5% NaCl and subjected to a negative potential corresponding to that induced by the cathodic corrosion protection system. The load was increased by a small amount every second day in order to establish the threshold stress for hydrogen cracking during service in seawater with hydrogen being introduced on the steel surface by the cathodic protection system. A significant influence of the second heat cycle was observed. This effect was attributed to both a variation in yield strength and the influence of precipitates on hydrogen solubility and diffusion.