Schottky anomaly

About: Schottky anomaly is a research topic. Over the lifetime, 362 publications have been published within this topic receiving 4171 citations.

Magnetization reversal and Yb3+/Cr3+ spin ordering at low temperature for perovskite YbCrO3 chromites

Abstract: The temperature dependence of the dc magnetization and the specific heat capacity are systematically investigated for the perovskite YbCrO3 chromites. The results show that there exist two complex sequences of magnetic transitions with the characteristics of magnetization reversal and Yb3+/Cr3+ spin ordering at different temperature, respectively. The antiferromagneticlike transition around TN=118 K is attributed to the antiferromagnetic ordering of the Cr3+ spins and a negative magnetization, accompanied with a tendency to the plateau below 10 K caused by the Yb3+ ordering. We obtain the Weiss constant of −197.0 K and an effective moment of 5.99μB for the sum of the free ion values of 4.53μB for Yb3+ and 3.87μB for high-spin Cr3+ from the experiments, which shows an antiferromagnetic interaction and the existence of weak canted antiferromagnetic (CAFM) characteristics. Corresponding to the magnetic phase transition in the Cr sublattice, the specific heat capacity under zero fields exhibits a sharp λ-shap...

Neutron spectroscopic determination of the crystalline electric field in HoBa 2 Cu 3 O 7 − δ

Abstract: Inelastic neutron scattering has been employed to study the crystalline electric field (CEF) interaction in the high-T/sub c/ superconductor HoBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/. The CEF at the Ho site completely lifts the 17-fold degeneracy of the ground-state J multiplet. The observed energy spectra exhibit a large number of well-resolved CEF transitions between 0.5 and 73 meV, so that we have been able to assign the energies of ten excited CEF levels. On the basis of the observed intensities we have been able to unambiguously determine all nine CEF parameters required for orthorhombic symmetry. The CEF parameters turn out to be incompatible with any kind of point-charge calculation as expected. The results are used to predict the magnetization and the field-dependent Schottky anomaly of the heat capacity of HoBa/sub 2/Cu/sub 3/O/sub 7/ as well as to extrapolate the CEF interaction to ErBa/sub 2/Cu/sub 3/O/sub 7/, which yields good agreement with the experimental data.

Simple glass-forming liquids: their definition, fragilities, and landscape excitation profiles

Abstract: The `excitation profile' of a liquid is a measure of the rate per kelvin at which the liquid is driven by entropy generation to the top of its potential energy landscape. We argue that it determines the liquid fragility, and hence controls the canonical features of viscous liquid phenomenology. We seek to prove this using studies of simple glass formers. We recognize two types of simple glass former, molecularly simple and excitationally simple, and provide examples and characterization of each. In the first category we describe the systems , , and their binary solutions. The simplest case is only glass forming in emulsion form but solutions in up to 85% are found to be bulk glass formers. The fragility of each component is determined by the new `reduced-transition-width' measurement and found to be only 60% fragile versus 75% for the fragile liquid toluene and propylene carbonate. We infer that the mixed LJ (Lennard-Jones) system, whose landscape `excitation profile' has recently been determined by MD computer simulations, is only a moderately fragile liquid. For the increase in heat capacity at is used to `quantify' the energy landscape and establish the appropriate `excitation profile' for liquids of this fragility. The second type of simplicity is bestowed by the presence of a single dominant interaction in the system. The best cases are the covalent glass formers of the chalcogenide variety, e.g. Ge-Se, and Ge-As-Se, in which the breaking of angle-specific covalent bonds is the dominant excitation process. We show that in the ground-state bond lattice an extremum in the glass transition temperature occurs close to the theoretical rigidity percolation bond density of 2.4 bonds per particle where a fragility minimum is also found. Invoking a simple theoretical treatment of this bond lattice we find that the entropy of the elementary excitation is a minimum or zero at percolation, and the glass transition becomes a simple Schottky anomaly with kinetic arrest. The excitation profile predicted by this model seems similar to that found by the simulations for the molecularly simple glasses. The fragility of the liquid is, in this case, controlled by the entropy change in the elementary excitation process. Whether this excitation entropy is determined within the configurational or vibrational densitites of states is a key question. In either case, large values mean sharp excitation profiles which, due to cooperative effects near pure Ge, can become first-order liquid-liquid transitions.

Superconductivity at 5 K in NdO0.5F0.5BiS2

Abstract: We report appearance of superconductivity at 5 K in NdO0.5F0.5BiS2 and supplement the discovery [Demura et al., e-print arXiv:1207.5248] of the same in layered sulfide based compound. Detailed structural analysis showed that the studied compound is crystallized in tetragonal P4/nmm space group with lattice parameters a = 3.9911(3) A and c = 13.3830(2) A. Bulk superconductivity is established in NdO0.5F0.5BiS2 at 5 K by both transport and magnetic measurements. Electrical transport measurements showed superconducting Tc onset at 5.2 K and Tc (ρ = 0) at 4.7 K. Under applied magnetic field, both Tc onset and Tc (ρ = 0) decrease to lower temperatures and an upper critical field [Hc2(0)] of above 23 kOe is estimated. Isothermal magnetization exhibited typical type-II behavior with lower critical field (Hc1) of around 25 Oe. Specific heat [Cp(T)] is investigated in the temperature range of 1.9–50 K in zero external magnetic field. A Schottky-type anomaly is observed at low temperature below 7 K.

Impurity bands in Kondo insulators.

Abstract: Kondo insulators like ${\mathrm{Ce}}_{3}$${\mathrm{Bi}}_{4}$${\mathrm{Pt}}_{3}$ and CeNiSn are compounds with small-band-gap semiconductor properties. Nonmagnetic impurities, so-called Kondo holes, break the translational invariance and hence the coherence of the ground state. Isolated impurities give rise to a bound state in the gap, which pins the Fermi level and has magnetic properties (Curie susceptibility and Schottky anomaly in the specific heat). A finite concentration of Kondo holes gives rise to an impurity band inside the gap of the f-electron density of states, whose height and width are proportional to \ensuremath{\surd}c for small concentrations. The specific heat is proportional to T at very low temperatures and the susceptibility is Pauli-like at low T. The correlations within the f band are introduced via a self-energy, evaluated to second-order perturbation in U. We use the (1/d)-expansion method of Schweitzer and Czycholl to leading order in which the k integrations are properly carried out, but the k dependence of the self-energy is neglected. The main effect of U is to narrow the gap, as well as the impurity band.