Mn site substitution of La0.67Ca0.33MnO3 with closed shell ions: Effect on magnetic transition temperature

Mn site is substituted with closed shell ions (Al, Ga, Ti, Zr and a certain combination of Zr and Al) and also with Fe and Ru ions carrying the magnetic moment (S=5/2 and 2 respectively) at a fixed concentration of 5 at %. Substitution did not change either the crystal symmetry or the oxygen stoichiometry. All substituents were found to suppress both the metal-insulator and ferromagnetic transition temperatures (T _p(ρ) and T _C, respectively) to varied extents. Two main contributions identified for the suppression are the lattice disorder arising due to difference in the ionic radii between the substituent (r _M) and the Mn³⁺ ion (r _Mn ³⁺) and in the case of the substituents carrying a magnetic moment, the type of magnetic coupling between the substituent and that of the neighboring Mn ion.     

Scaling of waves in the bak-tang-wiesenfeld sandpile model

We study probability distributions of waves of topplings in the Bak-Tang-Wiesenfeld model on hypercubic lattices for dimensions D>/=2. Waves represent relaxation processes which do not contain multiple toppling events. We investigate bulk and boundary waves by means of their correspondence to spanning trees, and by extensive numerical simulations. While the scaling behavior of avalanches is complex and usually not governed by simple scaling laws, we show that the probability distributions for waves display clear power-law asymptotic behavior in perfect agreement with the analytical predictions. Critical exponents are obtained for the distributions of radius, area, and duration of bulk and boundary waves. Relations between them and fractal dimensions of waves are derived. We confirm that the upper critical dimension D(u) of the model is 4, and calculate logarithmic corrections to the scaling behavior of waves in D=4. In addition, we present analytical estimates for bulk avalanches in dimensions D>/=4 and simulation data for avalanches in D相似文献   

DSC analysis of Cu–Zn–Sn shape memory alloy fabricated via electrodeposition route

Cu–Zn–Sn shape memory alloy strips with composition range of 13.70–46.30 mass% Sn were fabricated by electrodepositing Sn on a shim brass surface and then subsequently annealed at a constant temperature of 400 °C for 120 min under flowing nitrogen. Subjecting the Sn-plated strips to differential scanning calorimetry (DSC) analysis revealed that the austenitic start (A _s) temperature was essentially constant at 225 °C while the martensite start (M _s) temperature was consistently within the 221.5–222 °C interval. Austenite to martensite phase transformation showed two distinct peaks on the DSC thermogram which can be attributed to the non-homogeneity of the bulk Cu–Zn–Sn ternary alloy. The latent heats of cooling and heating were found to increase with the mass% Sn plated on the shim brass. Effect of annealing temperature was also investigated wherein strips with an essentially constant composition of 26 mass% Sn were annealed at a temperature range of 350–420 °C for 120 min under flowing nitrogen. Varying the annealing temperature has no significant effect on the transformation temperatures of the ternary alloy.     

Minimal Sandpiles on Hexagonal Lattice

We study the minimal recurrent configurations of the Abelian sandpile model on the hexagonal lattice referred to the dynamics of a nonconservative sandpile model. The one-to-one correspondence between these configurations and the set of maximally oriented spanning trees on the triangular sublattice is constructed. We derive the correlation functions in minimal recurrent configurations on a quasi-one-dimensional 2 × N lattice, compare them with correlations for ordinary recurrent configurations, and argue for asymptotic equivalence between them.     

Experimental evidence of time-delay-induced death in coupled limit-cycle oscillators

Experimental observations of time-delay-induced amplitude death in two coupled nonlinear electronic circuits that are individually capable of exhibiting limit-cycle oscillations are described. The existence of multiply connected death islands in the parameter space of coupling strength and time delay for coupled identical oscillators is established. The existence of such regions was predicted earlier on theoretical grounds [Phys. Rev. Lett. 80, 5109 (1998); Physica (Amsterdam) 129D, 15 (1999)]. The experiments also reveal the occurrence of multiple frequency states, frequency suppression of oscillations with increased time delay, and the onset of both in-phase and antiphase collective oscillations.