Study on domain and domain dynamics in two-dimensional ferromagnetic thin films

Abstract

Study on domain and domain dynamics in two-dimensional ferromagnetic thin films is a challenging issue in magnetism as well as in spintronics. Recently, understanding domain and domain dynamics has been tremendously enhanced by means of advanced domain imaging techniques, which are capable of direct observation of the domain configurations and domain evolution patterns. We have investigated the domain structure and domain reversal behavior in two typical ferromagnetic thin film systems such as the Co/Pd multilayer system with perpendicular magnetic anisotropy and the MnAs/GaAs(001) system with in-plane magnetic anisotropy. In our study, the domain structure was investigated using a magnetic force microscope (MFM) system, equipped with an electromagnet which allows to investigate the evolution of the magnetic domains in an in-plane applied magnetic field. Also, the domain reversal behavior was investigated by means of a magneto-optical Kerr effect microscope magnetometer (MOMM), capable of direct time-resolved observation of magnetic domain patterns and simultaneously measuring the local magnetic properties on a submicrometer spatial resolution. We investigate the thermally activated domain reversal of Co/Pd multilayers with uniaxial perpendicular anisotropy using the MOMM equipped with a magnetic pulse generator in a wide time range of ㎲ ~ s. It is found that the energy barrier in the thermally activated process is nonlinearly dependent on the applied field, irrespective of the difference in the domain evolution processes of wall-motion, dendrite-growth, and nucleation. These results are well explained by a theoretical model considering a ferromagnetic thin film with uniaxial perpendicular anisotropy. Also, it is found that the field dependence of the activation volumes is characterized by the difference between the domain wall energy and the dipolar energy. We report the change of the magnetic domain structure, dependent on the film thickness of the MnAs f...