Dynamics and scaling behavior of magnetic domain in ferromagnetic nanothin films

Abstract

The geometry and dynamics of magnetic domain in ultrathin ferromagnetic films and nanomultilayers are of fundamental interests, because the nature of domain and domain dynamics in these systems plays a key role in determining their important magnetic properties such as the domain formation and the magnetization reversal. From the technological point of view, interest in the geometry and dynamics of magnetic domain in these system has grown rapidly motivated by the possible application to information storage technology and upcoming magnetoelectronics. In this study, we have investigated the magnetic domain configurations, domain dynamics, and their scaling behavior in various ferromagnetic thin films such as Co, Co/Pd, and Co/Pt systems. To study the geometry and dynamics of magnetic domain, we have developed a high-performance magnetooptical microscope magnetometer (MOMM) system, which basically consists of a polarizing optical microscope, digital intensifying-CCD, and high-speed frame grabber to observe and store the image of magnetic domain via magnetooptical Kerr effect (MOKE). The system is capable of real-time domain observation with the spatial resolution of 0.4㎛ and the Kerr angle resolution of 0.1˚ at x1,000 magnification. By controlling the optical illumination path, we can provide an incident angle of 0 to 20˚ from the film normal and thus, we can observe magnetic domains of sample having perpendicular magnetic anisotropy via polar MOKE with normal incidence as well as sample having in-plane magnetic anisotropy via longitudinal MOKE with oblique incidence. By means of MOMM, we first report direct full-field observation of Barkhausen avalanches in Co polycrystalline thin films at criticality, where we can find dynamic scaling behavior of Barkhausen jump size. The Barkhausen jump size shows power-law scaling distribution with critical exponent τ=1.30±0.05, which is accordant to the two-dimensional prediction of the theoretical model originally prop...