S. L. A. de Queiroz

DOMAIN SIZE EFFECTS IN BARKHAUSEN NOISE

The possible existence of self-organized criticality in Barkhausen noise is investigated theoretically through a single interface model, and experimentally from measurements in amorphous magnetostrictive ribbon Metglas 2605TCA under stress. Contrary to previous interpretations in the literature, both simulation and experiment indicate that the presence of a cutoff in the avalanche size distribution may be attributed to finite-size effects.

Finite driving rates in interface models of Barkhausen noise.

We consider a single-interface model for the description of Barkhausen noise in soft ferromagnetic materials. Previously, the model was used only in the adiabatic regime of infinitely slow field ramping. We introduce finite driving rates and analyze the scaling of event sizes and durations for different regimes of the driving rate. Coexistence of intermittency, with nontrivial scaling laws, and finite-velocity interface motion is observed for high enough driving rates. Power spectra show a decay approximately omega(-t), with t<2 for finite driving rates, revealing the influence of the internal structure of avalanches.

Multicritical point of ising spin glasses on triangular and honeycomb lattices

The behavior of two-dimensional Ising spin glasses at the multicritical point on triangular and honeycomb lattices is investigated with the help of finite-size scaling and conformal-invariance concepts. We use transfer-matrix methods on long strips to calculate domain-wall energies, uniform susceptibilities, and spin-spin correlation functions. Accurate estimates are provided for the location of the multicritical point on both lattices, which lend strong support to a conjecture recently advanced by Takeda, Sasamoto, and Nishimori. Correlation functions are shown to obey rather strict conformal-invariance requirements, once suitable adaptations are made to account for geometric aspects of the transfer-matrix description of triangular and honeycomb lattices. The universality class of critical behavior upon crossing the ferro-para-magnetic phase boundary is probed, with the following estimates for the associated critical indices:

Reentrant behavior and universality in the Anderson transition

\ensuremath{\nu}=1.49(2)

Specific Heat Singularity in Two-Dimensional Random Ising Ferromagnets

,

Superfluid transition of 4He in fractal media

\ensuremath{\gamma}=2.71(4)

Location and properties of the multicritical point in the Gaussian and ±J Ising spin glasses

,

Failure of single-parameter scaling of wave functions in Anderson localization

{\ensuremath{\eta}}_{1}=0.183(3)

Critical exponents for high density and bootstrap percolation

, which are distinctly different from the percolation values.

Correlation-function distributions at the Nishimori point of two-dimensional Ising spin glasses

The three-dimensional Anderson model with a rectangular distribution of site disorder displays two distinct localization-delocalization transitions, against varying disorder intensity, for a relatively narrow range of Fermi energies. Such transitions are studied through the calculation of localization lengths of quasi-- one-dimensional systems by transfer-matrix methods, and their analysis by finite-size scaling techniques. For the transition at higher disorder we find the localization-length exponent