The phase diagram of the double perovskites of the type Sr 2Ϫx La x FeMoO 6 is analyzed, with and without disorder due to antisites. In addition to an homogeneous half metallic ferrimagnetic phase in the absence of doping and disorder, we find antiferromagnetic phases at large dopings, and other ferrimagnetic phases with lower saturation magnetization, in the presence of disorder.

We present novel numerical evidence of spot self-replication controlled by noise in a simple autocatalytic reaction-diffusion system. The system dynamics exhibits a noise controlled transition from stripe growth to spot replication. The growth kinetics is also controlled by noise, and there is an optimal noise intensity for which the multiplication rate of spots is maximal. For larger noise intensities, the spots become unstable and the system is attracted by the trivial steady state. Some of the effects are reminiscent of both polymer chain and cell colony formation in random environments.

We present the phase structure of the chiral SU (2) × SU (2) scalarfermion model on the lattice using the Zaragoza proposal for chiral fermions. The numerical result agrees with an analytic study based on the use of weak and strong yukawa coupling expansions combined with the mean-field approach. The phase diagram consists of four phases: paramagnetic (PM), ferromagnetic (FM), antiferromagnetic (AFM) and ferrimagnetic (FI). The transition lines separating these four phases intersect at one quadruple point. * Laboratoire associé au CNRS

The nonequilibrium dynamic fluctuations of a stochastic version of the Gray-Scott ͑GS͒ model are studied analytically in leading order in perturbation theory by means of the dynamic renormalization group. There is an attracting stable fixed point at one-loop order, and the asymptotic scaling of the correlation functions is predicted for both spatial and temporally correlated noise sources. New effective three-body reaction terms, not present in the original GS model, are induced by the combined interplay of the fluctuations and nonlinearities.

Extraordinary magnetoresistance effect has been found in Ni/Co sputtered multilayers. Magnetoresistance values higher than 130% are achieved at room temperature with a saturation magnetic field of 35 Oe, using a particular arrangement of contacts. The large anisotropic magnetoresistance and the low coercivity of these samples are the origin of such an outstanding property. The results reported here seem to have promising applications in magnetoresistive devices.