Description of the figure from the article:
Magnetization jumps and the Barkhausen effect. (a) Magnetization curve, as a function of the time, of a 100-nm-thick ferromagnetic NiFe film submitted to a smooth, slow-varying external magnetic field. The magnification of the curve reveals that the change in magnetization is not smooth, but exhibits discrete and irregular jumps. The jumps of magnetization are due to the jerky motion of the magnetic domain walls in a disordered medium, a result of the interactions between DW and pinning centers, such as defects, impurities, dislocations, and grain boundaries. In a typical Barkhausen noise experiment, the changes of magnetization are detected by a pickup coil wound around the ferromagnetic material. As the magnetization changes, the respective variation of the magnetic flux induces a voltage signal in the coil that can be amplified and recorded. (b) The crackling response in magnetic systems is the Barkhausen noise, which itself consists in the time series of voltage pulses detected by the pickup coil. Notice that the Barkhausen noise shown in (b) is proportional to the time derivative of the magnetization in (a). The noise in correspondence to the magnetization jumps is a series of Barkhausen avalanches with broad range of sizes and durations. The inset shows an example of how the avalanches are extracted. A threshold (dashed line) is set to properly define the beginning and end of each Barkhausen avalanche. Three different avalanches are denoted here by the gray zones. The duration of the example avalanches is marked by solid intervals. The duration T is thus estimated as the time interval between the two successive intersections of the signal with the threshold. The area underneath the avalanche signal, between the same points, is defined as the avalanche size s.