Critical Scaling Behavior of Barkhausen Avalanches in Ferromagnetic Nanothin Films

It is recognized that the magnetization reverses with a sequence of discrete and jerky jumps, known as the Barkhausen effect. Recently, interest in the Barkhausen effect has grown as it is a good example of dynamical critical behavior, evidenced by experimental observation of a power law distribution of the Barkhausen jump size. So far, most experimental studies have been carried out on bulk samples using a classical inductive technique, which is difficult to apply to thin film samples mainly due to the ]ow signal intensity. For this reason, very few experiments have been done on two-dimensional ferromagnetic thin films. In this talk, we report a direct domain observation of Barkhausen avalanche at criticality in Co and MnAs thin films investigated by means of a magnetooptical microscope magnetometer (MOMM), capable of time-resolved domain observation with an image grabbing rate of 30 frames/s in real time. In Fig. 1, we demonstrate a series of six representative domain-evolution patterns of 25-nm Co film observed successively by means of the MOMM, where one can directly witness Barkhausen avalanche.