Jerky flow in dilute alloys, or the Portevin-Le Chatelier effect, is investigated using statistical analysis of time series characterizing the evolution of the plastic activity at distinct scales of observation, namely, the macroscopic scale of stress serrations and a mesoscopic scale pertaining to the accompanying acoustic emission. Whereas the stress serrations display various types of statistical distributions depending on the driving strain rate, including power-law, peaked and bimodal histograms, it is found that acoustic emission is characterized by power-law statistics of event size in all experimental conditions. The latter reflect intermittency and self-organization of plastic activity at a mesoscopic scale. This shift in the observed dynamics when the observation length scale is decreased is discussed in terms of the synchronization of small-scale events.

Real-time magneto-optical indicator film images reveal distinct asymmetry in the motion of a single domain wall in a wedged-NiFe /uniform-FeMn bilayer due to the nucleation and behavior of an exchange spring in the antiferromagnetic layer. Magnetization reversal from the ground state begins at the thick end of the wedge where the exchange anisotropy field ͑H E ͒ is minimal and the magnetostatic field ͑H MS ͒ is maximal, whereas reversal into the ground state begins from the thin end where H E is maximal and H MS is minimal.

Magnetization reversal processes in epitaxial NiO/NiFe bilayers were studied using the magneto-optic indicator film technique. The influence of dislocations on these processes was determined. Remagnetization parallel to the unidirectional anisotropy axis proceeds by domain nucleation and growth, with nucleation center activity being asymmetric with respect to the applied field sign. Magnetization reversal in the hard axis direction occurs by incoherent rotation. The enhanced coercivity and asymmetric nucleation can be explained by taking into account domain wall behavior in the antiferromagnetic layer.

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Magneto-optical imaging has revealed new features crucial for the understanding of the exchange bias phenomenon. We have observed hybrid domain walls consisting of ferromagnetic ͑FM͒ and antiferromagnetic sections and their evolution. The external magnetic field moves only the ferromagnetic section of the hybrid domain walls, leading to the formation of an exchange spring parallel to the interface. The nucleation and unwinding of the exchange spring occur at different locations and its propagation depends on the chirality of the FM domain walls. The stationary antiferromagnetic sections of the hybrid domain walls define the antiferromagnetic domains.

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Avalanchelike behavior reflected in power-law statistics is a ubiquitous property of extended systems addressed in a number of generic models. The paper presents an experimental investigation of the effect of thresholding on the statistics of durations and waiting times between avalanches using acoustic emission accompanying unstable plastic deformation. It is found that durations of acoustic events obey power-law statistical distributions robust against thresholding. The quiescent time distributions follow the Poisson law for low threshold values. Both these results corroborate the hypothesis that plastic deformation is akin to the phenomena associated with self-organized criticality (SOC), often advanced on the basis of power-law amplitude statistics. Increasing the threshold height enforces deviation from the Poisson distributions toward apparent power-law behavior. Such a thresholding effect may hinder the experimental determination of SOC-like dynamics because of the inevitable noise.

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