Magneto-Optical Studies of Magnetic Ultrathin Film Structures

Abstract

The specificities and advantages of magneto‐optics (MO) for studying the magnetism of thin film structures: sensitivity, high space and time resolution, and wavelength discrimination, are reviewed. Based on MO imaging experiments, two fundamental studies on the dynamics of the magnetization reversal in an ultrathin cobalt magnetic layer with perpendicular anisotropy and related dot arrays, or of the thermomagnetic MO recording–writing process, are presented.

Observation of Unequal Activation Volumes of Wall-Motion and Nucleation Processes inCo/PdMultilayers

“…Magnetization reversal dynamics in ferromagnetic thin films continues to be an important issue in achieving high performance of technological applications as well as in exploring fundamental issues in magnetism [1][2][3][4][5]. Recently, understanding of magnetization reversal dynamics has progressed greatly, largely motivated by direct observation of domain evolution patterns using magnetic imaging techniques, as well as by experimental observation of contrasting reversal behavior among similar samples of many systems [4][5][6][7][8].…”

“…Recently, understanding of magnetization reversal dynamics has progressed greatly, largely motivated by direct observation of domain evolution patterns using magnetic imaging techniques, as well as by experimental observation of contrasting reversal behavior among similar samples of many systems [4][5][6][7][8]. It is now well known that the magnetization reversal in ferromagnetic thin films occurs via two fundamental processes: wall motion from existing domains and nucleation of new domains at random positions respective to existing domains.…”

“…It is now well known that the magnetization reversal in ferromagnetic thin films occurs via two fundamental processes: wall motion from existing domains and nucleation of new domains at random positions respective to existing domains. The wall-motion process takes place either by a successive switching of activation volumes adjacent to existing domains via thermal activation energy overcoming finite wall-pinning energy when an applied field is smaller than the wall-pinning field of a film or by a viscous wall-motion process when an applied field is higher than the wall-pinning field of a film [4,8]. On the other hand, the nucleation process occurs by random switching of activation volumes at random places via thermal activation energy overcoming the energy barrier of nucleation.…”

“…Much effort has been devoted to characterize the activation volumes of the wall-motion and nucleation processes in a number of systems [4,7,8,13,14]. For instance, Labrune et al [13] demonstrated that the two activation volumes were almost identical in rare-earth transition-metal alloys, evidenced by no field dependence of the shape of magnetization viscosity curves.…”

“…The contrasting reversal modes were characterized quantitatively by the reversal ratio V ͞R: wall-motion dominant reversal for a sample having a ratio larger than 1 mm 3 , while a nucleation dominant one for a sample having a ratio smaller than 1 mm 3 . The reversal ratio indicates the difference between the activation energies of the two reversal processes [4,8] and, also, relates directly with the Fatuzzo's parameter ( V ͞Rr 0 ) which characterizes the magnetization viscosity curve [13,19].…”