Geometry of the valence transition induced surface reconstruction of Sm(0001)

We present a structural determination of the surface reconstruction of the Sm(0001) surface using surface x-ray diffraction, scanning tunneling microscopy, and ab initio calculations. The reconstruction is associated with a large (22%) expansion of the atomic radius for the top monolayer surface Sm atoms. The mechanism driving the surface reconstruction in Sm is unique among all elements and is connected to the strong correlations of the 4f electrons in Sm and the intermediate valence observed in certain Sm compounds. The atoms constituting the top monolayer of Sm(0001) have vastly different chemical properties compared to the layer underneath and behave as if they were an adsorbate of a different chemical species.     

Kinetic hindrance during the initial oxidation of Pd(100) at ambient pressures

The oxidation of the Pd(100) surface at oxygen pressures in the 10(-6) to 10(3) mbar range and temperatures up to 1000 K has been studied in situ by surface x-ray diffraction (SXRD). The results provide direct structural information on the phases present in the surface region and on the kinetics of the oxide formation. Depending on the (T,p) environmental conditions, we observe either a thin (sqrt[5]xsqrt[5])R27 degrees surface oxide or the growth of a rough, poorly ordered bulk oxide film of PdO predominantly with (001) orientation. By either comparison to the surface phase diagram from first-principles atomistic thermodynamics or by explicit time-resolved measurements we identify a strong kinetic hindrance to the bulk oxide formation even at temperatures as high as 675 K.     

Extensions of graph inversion to support an artificially intelligent modeling environment

This paper extends previous results in graph inversion to enable artificially intelligent model formulation by taking partial information from the problem domain into an algebraic form—that is, a mathematical model to support economicbased decision-making. Here focus is on flow relations and economic correlations. Issues of consistency are resolved, and a concept ofcore models is introduced to achieve minimality for simplifying model management and use. After establishing the general results, special consideration is given to input-output structures, as in Leontief models.     

Magnetocrystalline anisotropy of MnF2 deduced from static torque

The first anisotropy constant K₁ as well as the differential susceptibility ΔX = Xχ - X∥ of MnF₂ has been determined from static torque measurements. The temperature range was for K₁ 4.2 K to 66 K and for ΔX 4.2 K to 300 K. The result for K₁ is in good agreement with values obtained from antiferromagnetic resonance experiments. In order to explain the differential susceptibility in the paramagnetic region, it was found necessary to take the g-factor anisotropy into account.     

Specific heat and magnetic susceptibility of MnF2 and Mn0.98Fe0.02F2 near TN

The antiferro- to paramagnetic phase transition of the weakly anisotropic compound MnF₂ has been studied by means of heat capacity, magnetic susceptibility and thermal expansion measurements. The critical-point parameters associated with the specific heat indicate a transition according to the theoretical Ising-model. The temperature derivative of the parallel magnetic susceptibility times temperature (d(χ∥T)/dT) and the c-axis thermal expansion coefficient show a critical behaviour very similar to that of the specific heat. The influence of iron doping on the critical behaviour has been investigated by studies on Mn_0.98Fe_0.02F₂. Specific heat and magnetic susceptibility measurements show an unexpectedly sharp transition although some rounding off is noticed as compared to pure MnF₂.