Elastic Deformation of Polycrystals

We propose a framework to model elastic properties of polycrystals by coupling crystal orientational degrees of freedom with elastic strains. Our model encodes crystal symmetries and takes into account explicitly the strain compatibility induced long-range interaction between grains. The coupling of crystal orientation and elastic interactions allows for the rotation of individual grains by an external load. We apply the model to simulate uniaxial tensile loading of a 2D polycrystal within linear elasticity and a system with elastic anharmonicities that describe structural phase transformations. We investigate the constitutive response of the polycrystal and compare it to that of single crystals with crystallographic orientations that form the polycrystal.Comment: 4 pages, 4 ps figure

Valency of rare earths in RIn3 and RSn3: Ab initio analysis of electric-field gradients

In RIn3 and RSn3 the rare earth (R) is trivalent, except for Eu and Yb, which are divalent. This was experimentally determined in 1977 by perturbed angular correlation measurements of the electric-field gradient on a 111Cd impurity. At that time, the data were interpreted using a point charge model, which is now known to be unphysical and unreliable. This makes the valency determination potentially questionable. We revisit these data, and analyze them using ab initio calculations of the electric-field gradient. From these calculations, the physical mechanism that is responsible for the influence of the valency on the electric-field gradient is derived. A generally applicable scheme to interpret electric-field gradients is used, which in a transparent way correlates the size of the field gradient with chemical properties of the system.Comment: 10 page

Thermodynamic Properties of the One-Dimensional Extended Quantum Compass Model in the Presence of a Transverse Field

The presence of a quantum critical point can significantly affect the thermodynamic properties of a material at finite temperatures. This is reflected, e.g., in the entropy landscape S(T; c) in the vicinity of a quantum critical point, yielding particularly strong variations for varying the tuning parameter c such as magnetic field. In this work we have studied the thermodynamic properties of the quantum compass model in the presence of a transverse field. The specific heat, entropy and cooling rate under an adiabatic demagnetization process have been calculated. During an adiabatic (de)magnetization process temperature drops in the vicinity of a field-induced zero-temperature quantum phase transitions. However close to field-induced quantum phase transitions we observe a large magnetocaloric effect

Dynamical Mean-Field Theory and Its Applications to Real Materials

Dynamical mean-field theory (DMFT) is a non-perturbative technique for the investigation of correlated electron systems. Its combination with the local density approximation (LDA) has recently led to a material-specific computational scheme for the ab initio investigation of correlated electron materials. The set-up of this approach and its application to materials such as (Sr,Ca)VO_3, V_2O_3, and Cerium is discussed. The calculated spectra are compared with the spectroscopically measured electronic excitation spectra. The surprising similarity between the spectra of the single-impurity Anderson model and of correlated bulk materials is also addressed.Comment: 20 pages, 9 figures, invited paper for the JPSJ Special Issue "Kondo Effect - 40 Years after the Discovery"; final version, references adde

First-principles calculation of the thermal properties of silver

The thermal properties of silver are calculated within the quasi-harmonic approximation, by using phonon dispersions from density-functional perturbation theory, and the pseudopotential plane-wave method. The resulting free energy provides predictions for the temperature dependence of various quantities such as the equilibrium lattice parameter, the bulk modulus, and the heat capacity. Our results for the thermal properties are in good agreement with available experimental data in a wide range of temperatures. As a by-product, we calculate phonon frequency and Grueneisen parameter dispersion curves which are also in good agreement with experiment.Comment: 9 pages, 8 figures, submitted to Phys. Rev. B April 30, 1998). Other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm

Evidence for spin mixing in holmium thin film and crystal samples

144518Quantum Matter and Optic

Low temperature magnetic behavior in CePtGa₃

A low temperature study of CePtGa3 shows a peak in the heat capacity of ∼2.8 J/mol Ce K at 1.7 K, which is shifted to higher temperatures (∼6 K at 9.8 T) in magnetic fields. Furthermore, the heat capacity data are consistent with spin-glass-like behavior. The 8 T field data below 0.2 K suggests a γ of ∼120 mJ/mol Ce K2. AC magnetic susceptibility data as a function of the magnetic field (up to 2 T) suggests some small fraction of the Ce spins are involved with percolating antiferromagnetic clusters. Unlike the ordinary spin glasses, the Ce3+ ions in CePtGa3 occupy periodic lattice sites. The random RKKY interactions between spins which provides the basis for spin-glass-like behavior is induced by the random distribution of Pt and Ga atoms around the Ce3+ ions

Magnetic susceptibility and low-temperature heat capacity of CePd₃B_0.3

The heat capacity of CePd3B0.3 has been measured between 80 mK and 2.5 K in zero and applied fields up to 4 T. The specific heat exhibits a Schottky-like anomaly, nearly symmetric on a lnT scale, which is shifted to higher temperatures in applied fields. High-temperature susceptibility measurements confirm a near trivalent state of Ce in CePd3B0.3 while the ac susceptibility in the range 0.15 to 0.7 K displays a cusp at 0.45 K which is smeared out in applied fields indicating a spin-glass transition. Kondo interactions are also operative as evidenced by the large value of C/T as T→0